jdk8-mips64-public/langtools: src/share/classes/com/sun/tools/javac/comp/Infer.java@c6d5efccedc3 (annotated)

src/share/classes/com/sun/tools/javac/comp/Infer.java@c6d5efccedc3 (annotated)

src/share/classes/com/sun/tools/javac/comp/Infer.java

Fri, 20 Jun 2014 20:36:54 +0100

author: vromero
date: Fri, 20 Jun 2014 20:36:54 +0100
changeset 2543: c6d5efccedc3
parent 2384: 327122b01a9e
child 2601: 8dcde670aed3
permissions: -rw-r--r--

8044546: Crash on faulty reduce/lambda
Reviewed-by: mcimadamore, dlsmith
Contributed-by: maurizio.cimadamore@oracle.com, vicente.romero@oracle.com

 /*
  * Copyright (c) 1999, 2014, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */
 package com.sun.tools.javac.comp;
 import com.sun.tools.javac.tree.JCTree;
 import com.sun.tools.javac.tree.JCTree.JCTypeCast;
 import com.sun.tools.javac.tree.TreeInfo;
 import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 import com.sun.tools.javac.util.List;
 import com.sun.tools.javac.code.*;
 import com.sun.tools.javac.code.Type.*;
 import com.sun.tools.javac.code.Type.UndetVar.InferenceBound;
 import com.sun.tools.javac.code.Symbol.*;
 import com.sun.tools.javac.comp.DeferredAttr.AttrMode;
 import com.sun.tools.javac.comp.Infer.GraphSolver.InferenceGraph;
 import com.sun.tools.javac.comp.Infer.GraphSolver.InferenceGraph.Node;
 import com.sun.tools.javac.comp.Resolve.InapplicableMethodException;
 import com.sun.tools.javac.comp.Resolve.VerboseResolutionMode;
 import com.sun.tools.javac.util.GraphUtils.TarjanNode;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumMap;
 import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
 import static com.sun.tools.javac.code.TypeTag.*;
 /** Helper class for type parameter inference, used by the attribution phase.
  *
  *  <p><b>This is NOT part of any supported API.
  *  If you write code that depends on this, you do so at your own risk.
  *  This code and its internal interfaces are subject to change or
  *  deletion without notice.</b>
  */
 public class Infer {
     protected static final Context.Key<Infer> inferKey =
         new Context.Key<Infer>();
     Resolve rs;
     Check chk;
     Symtab syms;
     Types types;
     JCDiagnostic.Factory diags;
     Log log;
     /** should the graph solver be used? */
     boolean allowGraphInference;
     public static Infer instance(Context context) {
         Infer instance = context.get(inferKey);
         if (instance == null)
             instance = new Infer(context);
         return instance;
     }
     protected Infer(Context context) {
         context.put(inferKey, this);
         rs = Resolve.instance(context);
         chk = Check.instance(context);
         syms = Symtab.instance(context);
         types = Types.instance(context);
         diags = JCDiagnostic.Factory.instance(context);
         log = Log.instance(context);
         inferenceException = new InferenceException(diags);
         Options options = Options.instance(context);
         allowGraphInference = Source.instance(context).allowGraphInference()
                 && options.isUnset("useLegacyInference");
     }
     /** A value for prototypes that admit any type, including polymorphic ones. */
     public static final Type anyPoly = new JCNoType();
    /**
     * This exception class is design to store a list of diagnostics corresponding
     * to inference errors that can arise during a method applicability check.
     */
     public static class InferenceException extends InapplicableMethodException {
         private static final long serialVersionUID = 0;
         List<JCDiagnostic> messages = List.nil();
         InferenceException(JCDiagnostic.Factory diags) {
             super(diags);
         }
         @Override
         InapplicableMethodException setMessage() {
             //no message to set
             return this;
         }
         @Override
         InapplicableMethodException setMessage(JCDiagnostic diag) {
             messages = messages.append(diag);
             return this;
         }
         @Override
         public JCDiagnostic getDiagnostic() {
             return messages.head;
         }
         void clear() {
             messages = List.nil();
         }
     }
     protected final InferenceException inferenceException;
     // <editor-fold defaultstate="collapsed" desc="Inference routines">
     /**
      * Main inference entry point - instantiate a generic method type
      * using given argument types and (possibly) an expected target-type.
      */
     Type instantiateMethod( Env<AttrContext> env,
                             List<Type> tvars,
                             MethodType mt,
                             Attr.ResultInfo resultInfo,
                             MethodSymbol msym,
                             List<Type> argtypes,
                             boolean allowBoxing,
                             boolean useVarargs,
                             Resolve.MethodResolutionContext resolveContext,
                             Warner warn) throws InferenceException {
         //-System.err.println("instantiateMethod(" + tvars + ", " + mt + ", " + argtypes + ")"); //DEBUG
         final InferenceContext inferenceContext = new InferenceContext(tvars);  //B0
         inferenceException.clear();
         try {
             DeferredAttr.DeferredAttrContext deferredAttrContext =
                         resolveContext.deferredAttrContext(msym, inferenceContext, resultInfo, warn);
             resolveContext.methodCheck.argumentsAcceptable(env, deferredAttrContext,   //B2
                     argtypes, mt.getParameterTypes(), warn);
             if (allowGraphInference &&
                     resultInfo != null &&
                     !warn.hasNonSilentLint(Lint.LintCategory.UNCHECKED)) {
                 //inject return constraints earlier
                 checkWithinBounds(inferenceContext, warn); //propagation
                 Type newRestype = generateReturnConstraints(env.tree, resultInfo,  //B3
                         mt, inferenceContext);
                 mt = (MethodType)types.createMethodTypeWithReturn(mt, newRestype);
                 //propagate outwards if needed
                 if (resultInfo.checkContext.inferenceContext().free(resultInfo.pt)) {
                     //propagate inference context outwards and exit
                     inferenceContext.dupTo(resultInfo.checkContext.inferenceContext());
                     deferredAttrContext.complete();
                     return mt;
                 }
             }
             deferredAttrContext.complete();
             // minimize as yet undetermined type variables
             if (allowGraphInference) {
                 inferenceContext.solve(warn);
             } else {
                 inferenceContext.solveLegacy(true, warn, LegacyInferenceSteps.EQ_LOWER.steps); //minimizeInst
             }
             mt = (MethodType)inferenceContext.asInstType(mt);
             if (!allowGraphInference &&
                     inferenceContext.restvars().nonEmpty() &&
                     resultInfo != null &&
                     !warn.hasNonSilentLint(Lint.LintCategory.UNCHECKED)) {
                 generateReturnConstraints(env.tree, resultInfo, mt, inferenceContext);
                 inferenceContext.solveLegacy(false, warn, LegacyInferenceSteps.EQ_UPPER.steps); //maximizeInst
                 mt = (MethodType)inferenceContext.asInstType(mt);
             }
             if (resultInfo != null && rs.verboseResolutionMode.contains(VerboseResolutionMode.DEFERRED_INST)) {
                 log.note(env.tree.pos, "deferred.method.inst", msym, mt, resultInfo.pt);
             }
             // return instantiated version of method type
             return mt;
         } finally {
             if (resultInfo != null || !allowGraphInference) {
                 inferenceContext.notifyChange();
             } else {
                 inferenceContext.notifyChange(inferenceContext.boundedVars());
             }
             if (resultInfo == null) {
                 /* if the is no result info then we can clear the capture types
                  * cache without affecting any result info check
                  */
                 inferenceContext.captureTypeCache.clear();
             }
         }
     }
     /**
      * Generate constraints from the generic method's return type. If the method
      * call occurs in a context where a type T is expected, use the expected
      * type to derive more constraints on the generic method inference variables.
      */
     Type generateReturnConstraints(JCTree tree, Attr.ResultInfo resultInfo,
             MethodType mt, InferenceContext inferenceContext) {
         InferenceContext rsInfoInfContext = resultInfo.checkContext.inferenceContext();
         Type from = mt.getReturnType();
         if (mt.getReturnType().containsAny(inferenceContext.inferencevars) &&
                 rsInfoInfContext != emptyContext) {
             from = types.capture(from);
             //add synthetic captured ivars
             for (Type t : from.getTypeArguments()) {
                 if (t.hasTag(TYPEVAR) && ((TypeVar)t).isCaptured()) {
                     inferenceContext.addVar((TypeVar)t);
                 }
             }
         }
         Type qtype = inferenceContext.asUndetVar(from);
         Type to = resultInfo.pt;
         if (qtype.hasTag(VOID)) {
             to = syms.voidType;
         } else if (to.hasTag(NONE)) {
             to = from.isPrimitive() ? from : syms.objectType;
         } else if (qtype.hasTag(UNDETVAR)) {
             if (resultInfo.pt.isReference()) {
                 to = generateReturnConstraintsUndetVarToReference(
                         tree, (UndetVar)qtype, to, resultInfo, inferenceContext);
             } else {
                 if (to.isPrimitive()) {
                     to = generateReturnConstraintsPrimitive(tree, (UndetVar)qtype, to,
                         resultInfo, inferenceContext);
                 }
             }
         }
         Assert.check(allowGraphInference || !rsInfoInfContext.free(to),
                 "legacy inference engine cannot handle constraints on both sides of a subtyping assertion");
         //we need to skip capture?
         Warner retWarn = new Warner();
         if (!resultInfo.checkContext.compatible(qtype, rsInfoInfContext.asUndetVar(to), retWarn) ||
                 //unchecked conversion is not allowed in source 7 mode
                 (!allowGraphInference && retWarn.hasLint(Lint.LintCategory.UNCHECKED))) {
             throw inferenceException
                     .setMessage("infer.no.conforming.instance.exists",
                     inferenceContext.restvars(), mt.getReturnType(), to);
         }
         return from;
     }
     private Type generateReturnConstraintsPrimitive(JCTree tree, UndetVar from,
             Type to, Attr.ResultInfo resultInfo, InferenceContext inferenceContext) {
         if (!allowGraphInference) {
             //if legacy, just return boxed type
             return types.boxedClass(to).type;
         }
         //if graph inference we need to skip conflicting boxed bounds...
         for (Type t : from.getBounds(InferenceBound.EQ, InferenceBound.UPPER,
                 InferenceBound.LOWER)) {
             Type boundAsPrimitive = types.unboxedType(t);
             if (boundAsPrimitive == null || boundAsPrimitive.hasTag(NONE)) {
                 continue;
             }
             return generateReferenceToTargetConstraint(tree, from, to,
                     resultInfo, inferenceContext);
         }
         return types.boxedClass(to).type;
     }
     private Type generateReturnConstraintsUndetVarToReference(JCTree tree,
             UndetVar from, Type to, Attr.ResultInfo resultInfo,
             InferenceContext inferenceContext) {
         Type captureOfTo = types.capture(to);
         /* T is a reference type, but is not a wildcard-parameterized type, and either
          */
         if (captureOfTo == to) { //not a wildcard parameterized type
             /* i) B2 contains a bound of one of the forms alpha = S or S <: alpha,
              *      where S is a wildcard-parameterized type, or
              */
             for (Type t : from.getBounds(InferenceBound.EQ, InferenceBound.LOWER)) {
                 Type captureOfBound = types.capture(t);
                 if (captureOfBound != t) {
                     return generateReferenceToTargetConstraint(tree, from, to,
                             resultInfo, inferenceContext);
                 }
             }
             /* ii) B2 contains two bounds of the forms S1 <: alpha and S2 <: alpha,
              * where S1 and S2 have supertypes that are two different
              * parameterizations of the same generic class or interface.
              */
             for (Type aLowerBound : from.getBounds(InferenceBound.LOWER)) {
                 for (Type anotherLowerBound : from.getBounds(InferenceBound.LOWER)) {
                     if (aLowerBound != anotherLowerBound &&
                         commonSuperWithDiffParameterization(aLowerBound, anotherLowerBound)) {
                         /* self comment check if any lower bound may be and undetVar,
                          * in that case the result of this call may be a false positive.
                          * Should this be restricted to non free types?
                          */
                         return generateReferenceToTargetConstraint(tree, from, to,
                             resultInfo, inferenceContext);
                     }
                 }
             }
         }
         /* T is a parameterization of a generic class or interface, G,
          * and B2 contains a bound of one of the forms alpha = S or S <: alpha,
          * where there exists no type of the form G<...> that is a
          * supertype of S, but the raw type G is a supertype of S
          */
         if (to.isParameterized()) {
             for (Type t : from.getBounds(InferenceBound.EQ, InferenceBound.LOWER)) {
                 Type sup = types.asSuper(t, to.tsym);
                 if (sup != null && sup.isRaw()) {
                     return generateReferenceToTargetConstraint(tree, from, to,
                             resultInfo, inferenceContext);
                 }
             }
         }
         return to;
     }
     private boolean commonSuperWithDiffParameterization(Type t, Type s) {
         Pair<Type, Type> supers = getParameterizedSupers(t, s);
         return (supers != null && !types.isSameType(supers.fst, supers.snd));
     }
     private Type generateReferenceToTargetConstraint(JCTree tree, UndetVar from,
             Type to, Attr.ResultInfo resultInfo,
             InferenceContext inferenceContext) {
         inferenceContext.solve(List.of(from.qtype), new Warner());
         inferenceContext.notifyChange();
         Type capturedType = resultInfo.checkContext.inferenceContext()
                 .cachedCapture(tree, from.inst, false);
         if (types.isConvertible(capturedType,
                 resultInfo.checkContext.inferenceContext().asUndetVar(to))) {
             //effectively skip additional return-type constraint generation (compatibility)
             return syms.objectType;
         }
         return to;
     }
     /**
       * Infer cyclic inference variables as described in 15.12.2.8.
       */
     private void instantiateAsUninferredVars(List<Type> vars, InferenceContext inferenceContext) {
         ListBuffer<Type> todo = new ListBuffer<>();
         //step 1 - create fresh tvars
         for (Type t : vars) {
             UndetVar uv = (UndetVar)inferenceContext.asUndetVar(t);
             List<Type> upperBounds = uv.getBounds(InferenceBound.UPPER);
             if (Type.containsAny(upperBounds, vars)) {
                 TypeSymbol fresh_tvar = new TypeVariableSymbol(Flags.SYNTHETIC, uv.qtype.tsym.name, null, uv.qtype.tsym.owner);
                 fresh_tvar.type = new TypeVar(fresh_tvar, types.makeCompoundType(uv.getBounds(InferenceBound.UPPER)), null);
                 todo.append(uv);
                 uv.inst = fresh_tvar.type;
             } else if (upperBounds.nonEmpty()) {
                 uv.inst = types.glb(upperBounds);
             } else {
                 uv.inst = syms.objectType;
             }
         }
         //step 2 - replace fresh tvars in their bounds
         List<Type> formals = vars;
         for (Type t : todo) {
             UndetVar uv = (UndetVar)t;
             TypeVar ct = (TypeVar)uv.inst;
             ct.bound = types.glb(inferenceContext.asInstTypes(types.getBounds(ct)));
             if (ct.bound.isErroneous()) {
                 //report inference error if glb fails
                 reportBoundError(uv, BoundErrorKind.BAD_UPPER);
             }
             formals = formals.tail;
         }
     }
     /**
      * Compute a synthetic method type corresponding to the requested polymorphic
      * method signature. The target return type is computed from the immediately
      * enclosing scope surrounding the polymorphic-signature call.
      */
     Type instantiatePolymorphicSignatureInstance(Env<AttrContext> env,
                                             MethodSymbol spMethod,  // sig. poly. method or null if none
                                             Resolve.MethodResolutionContext resolveContext,
                                             List<Type> argtypes) {
         final Type restype;
         //The return type for a polymorphic signature call is computed from
         //the enclosing tree E, as follows: if E is a cast, then use the
         //target type of the cast expression as a return type; if E is an
         //expression statement, the return type is 'void' - otherwise the
         //return type is simply 'Object'. A correctness check ensures that
         //env.next refers to the lexically enclosing environment in which
         //the polymorphic signature call environment is nested.
         switch (env.next.tree.getTag()) {
             case TYPECAST:
                 JCTypeCast castTree = (JCTypeCast)env.next.tree;
                 restype = (TreeInfo.skipParens(castTree.expr) == env.tree) ?
                     castTree.clazz.type :
                     syms.objectType;
                 break;
             case EXEC:
                 JCTree.JCExpressionStatement execTree =
                         (JCTree.JCExpressionStatement)env.next.tree;
                 restype = (TreeInfo.skipParens(execTree.expr) == env.tree) ?
                     syms.voidType :
                     syms.objectType;
                 break;
             default:
                 restype = syms.objectType;
         }
         List<Type> paramtypes = Type.map(argtypes, new ImplicitArgType(spMethod, resolveContext.step));
         List<Type> exType = spMethod != null ?
             spMethod.getThrownTypes() :
             List.of(syms.throwableType); // make it throw all exceptions
         MethodType mtype = new MethodType(paramtypes,
                                           restype,
                                           exType,
                                           syms.methodClass);
         return mtype;
     }
     //where
         class ImplicitArgType extends DeferredAttr.DeferredTypeMap {
             public ImplicitArgType(Symbol msym, Resolve.MethodResolutionPhase phase) {
                 (rs.deferredAttr).super(AttrMode.SPECULATIVE, msym, phase);
             }
             public Type apply(Type t) {
                 t = types.erasure(super.apply(t));
                 if (t.hasTag(BOT))
                     // nulls type as the marker type Null (which has no instances)
                     // infer as java.lang.Void for now
                     t = types.boxedClass(syms.voidType).type;
                 return t;
             }
         }
     /**
       * This method is used to infer a suitable target SAM in case the original
       * SAM type contains one or more wildcards. An inference process is applied
       * so that wildcard bounds, as well as explicit lambda/method ref parameters
       * (where applicable) are used to constraint the solution.
       */
     public Type instantiateFunctionalInterface(DiagnosticPosition pos, Type funcInterface,
             List<Type> paramTypes, Check.CheckContext checkContext) {
         if (types.capture(funcInterface) == funcInterface) {
             //if capture doesn't change the type then return the target unchanged
             //(this means the target contains no wildcards!)
             return funcInterface;
         } else {
             Type formalInterface = funcInterface.tsym.type;
             InferenceContext funcInterfaceContext =
                     new InferenceContext(funcInterface.tsym.type.getTypeArguments());
             Assert.check(paramTypes != null);
             //get constraints from explicit params (this is done by
             //checking that explicit param types are equal to the ones
             //in the functional interface descriptors)
             List<Type> descParameterTypes = types.findDescriptorType(formalInterface).getParameterTypes();
             if (descParameterTypes.size() != paramTypes.size()) {
                 checkContext.report(pos, diags.fragment("incompatible.arg.types.in.lambda"));
                 return types.createErrorType(funcInterface);
             }
             for (Type p : descParameterTypes) {
                 if (!types.isSameType(funcInterfaceContext.asUndetVar(p), paramTypes.head)) {
                     checkContext.report(pos, diags.fragment("no.suitable.functional.intf.inst", funcInterface));
                     return types.createErrorType(funcInterface);
                 }
                 paramTypes = paramTypes.tail;
             }
             try {
                 funcInterfaceContext.solve(funcInterfaceContext.boundedVars(), types.noWarnings);
             } catch (InferenceException ex) {
                 checkContext.report(pos, diags.fragment("no.suitable.functional.intf.inst", funcInterface));
             }
             List<Type> actualTypeargs = funcInterface.getTypeArguments();
             for (Type t : funcInterfaceContext.undetvars) {
                 UndetVar uv = (UndetVar)t;
                 if (uv.inst == null) {
                     uv.inst = actualTypeargs.head;
                 }
                 actualTypeargs = actualTypeargs.tail;
             }
             Type owntype = funcInterfaceContext.asInstType(formalInterface);
             if (!chk.checkValidGenericType(owntype)) {
                 //if the inferred functional interface type is not well-formed,
                 //or if it's not a subtype of the original target, issue an error
                 checkContext.report(pos, diags.fragment("no.suitable.functional.intf.inst", funcInterface));
             }
             //propagate constraints as per JLS 18.2.1
             checkContext.compatible(owntype, funcInterface, types.noWarnings);
             return owntype;
         }
     }
     // </editor-fold>
     // <editor-fold defaultstate="collapsed" desc="Bound checking">
     /**
      * Check bounds and perform incorporation
      */
     void checkWithinBounds(InferenceContext inferenceContext,
                              Warner warn) throws InferenceException {
         MultiUndetVarListener mlistener = new MultiUndetVarListener(inferenceContext.undetvars);
         List<Type> saved_undet = inferenceContext.save();
         try {
             while (true) {
                 mlistener.reset();
                 if (!allowGraphInference) {
                     //in legacy mode we lack of transitivity, so bound check
                     //cannot be run in parallel with other incoprporation rounds
                     for (Type t : inferenceContext.undetvars) {
                         UndetVar uv = (UndetVar)t;
                         IncorporationStep.CHECK_BOUNDS.apply(uv, inferenceContext, warn);
                     }
                 }
                 for (Type t : inferenceContext.undetvars) {
                     UndetVar uv = (UndetVar)t;
                     //bound incorporation
                     EnumSet<IncorporationStep> incorporationSteps = allowGraphInference ?
                             incorporationStepsGraph : incorporationStepsLegacy;
                     for (IncorporationStep is : incorporationSteps) {
                         if (is.accepts(uv, inferenceContext)) {
                             is.apply(uv, inferenceContext, warn);
                         }
                     }
                 }
                 if (!mlistener.changed || !allowGraphInference) break;
             }
         }
         finally {
             mlistener.detach();
             if (incorporationCache.size() == MAX_INCORPORATION_STEPS) {
                 inferenceContext.rollback(saved_undet);
             }
             incorporationCache.clear();
         }
     }
     //where
         /**
          * This listener keeps track of changes on a group of inference variable
          * bounds. Note: the listener must be detached (calling corresponding
          * method) to make sure that the underlying inference variable is
          * left in a clean state.
          */
         class MultiUndetVarListener implements UndetVar.UndetVarListener {
             boolean changed;
             List<Type> undetvars;
             public MultiUndetVarListener(List<Type> undetvars) {
                 this.undetvars = undetvars;
                 for (Type t : undetvars) {
                     UndetVar uv = (UndetVar)t;
                     uv.listener = this;
                 }
             }
             public void varChanged(UndetVar uv, Set<InferenceBound> ibs) {
                 //avoid non-termination
                 if (incorporationCache.size() < MAX_INCORPORATION_STEPS) {
                     changed = true;
                 }
             }
             void reset() {
                 changed = false;
             }
             void detach() {
                 for (Type t : undetvars) {
                     UndetVar uv = (UndetVar)t;
                     uv.listener = null;
                 }
             }
         };
         /** max number of incorporation rounds */
         static final int MAX_INCORPORATION_STEPS = 100;
     /* If for two types t and s there is a least upper bound that is a
      * parameterized type G, then there exists a supertype of 't' of the form
      * G<T1, ..., Tn> and a supertype of 's' of the form G<S1, ..., Sn>
      * which will be returned by this method. If no such supertypes exists then
      * null is returned.
      *
      * As an example for the following input:
      *
      * t = java.util.ArrayList<java.lang.String>
      * s = java.util.List<T>
      *
      * we get this ouput:
      *
      * Pair[java.util.List<java.lang.String>,java.util.List<T>]
      */
     private Pair<Type, Type> getParameterizedSupers(Type t, Type s) {
         Type lubResult = types.lub(t, s);
         if (lubResult == syms.errType || lubResult == syms.botType ||
                 !lubResult.isParameterized()) {
             return null;
         }
         Type asSuperOfT = types.asSuper(t, lubResult.tsym);
         Type asSuperOfS = types.asSuper(s, lubResult.tsym);
         return new Pair<>(asSuperOfT, asSuperOfS);
     }
     /**
      * This enumeration defines an entry point for doing inference variable
      * bound incorporation - it can be used to inject custom incorporation
      * logic into the basic bound checking routine
      */
     enum IncorporationStep {
         /**
          * Performs basic bound checking - i.e. is the instantiated type for a given
          * inference variable compatible with its bounds?
          */
         CHECK_BOUNDS() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 uv.substBounds(inferenceContext.inferenceVars(), inferenceContext.instTypes(), infer.types);
                 infer.checkCompatibleUpperBounds(uv, inferenceContext);
                 if (uv.inst != null) {
                     Type inst = uv.inst;
                     for (Type u : uv.getBounds(InferenceBound.UPPER)) {
                         if (!isSubtype(inst, inferenceContext.asUndetVar(u), warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.UPPER);
                         }
                     }
                     for (Type l : uv.getBounds(InferenceBound.LOWER)) {
                         if (!isSubtype(inferenceContext.asUndetVar(l), inst, warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.LOWER);
                         }
                     }
                     for (Type e : uv.getBounds(InferenceBound.EQ)) {
                         if (!isSameType(inst, inferenceContext.asUndetVar(e), infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.EQ);
                         }
                     }
                 }
             }
             @Override
             boolean accepts(UndetVar uv, InferenceContext inferenceContext) {
                 //applies to all undetvars
                 return true;
             }
         },
         /**
          * Check consistency of equality constraints. This is a slightly more aggressive
          * inference routine that is designed as to maximize compatibility with JDK 7.
          * Note: this is not used in graph mode.
          */
         EQ_CHECK_LEGACY() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 Type eq = null;
                 for (Type e : uv.getBounds(InferenceBound.EQ)) {
                     Assert.check(!inferenceContext.free(e));
                     if (eq != null && !isSameType(e, eq, infer)) {
                         infer.reportBoundError(uv, BoundErrorKind.EQ);
                     }
                     eq = e;
                     for (Type l : uv.getBounds(InferenceBound.LOWER)) {
                         Assert.check(!inferenceContext.free(l));
                         if (!isSubtype(l, e, warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.BAD_EQ_LOWER);
                         }
                     }
                     for (Type u : uv.getBounds(InferenceBound.UPPER)) {
                         if (inferenceContext.free(u)) continue;
                         if (!isSubtype(e, u, warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.BAD_EQ_UPPER);
                         }
                     }
                 }
             }
         },
         /**
          * Check consistency of equality constraints.
          */
         EQ_CHECK() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type e : uv.getBounds(InferenceBound.EQ)) {
                     if (e.containsAny(inferenceContext.inferenceVars())) continue;
                     for (Type u : uv.getBounds(InferenceBound.UPPER)) {
                         if (!isSubtype(e, inferenceContext.asUndetVar(u), warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.BAD_EQ_UPPER);
                         }
                     }
                     for (Type l : uv.getBounds(InferenceBound.LOWER)) {
                         if (!isSubtype(inferenceContext.asUndetVar(l), e, warn, infer)) {
                             infer.reportBoundError(uv, BoundErrorKind.BAD_EQ_LOWER);
                         }
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha <: T} and {@code alpha :> S}
          * perform {@code S <: T} (which could lead to new bounds).
          */
         CROSS_UPPER_LOWER() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b1 : uv.getBounds(InferenceBound.UPPER)) {
                     for (Type b2 : uv.getBounds(InferenceBound.LOWER)) {
                         isSubtype(inferenceContext.asUndetVar(b2), inferenceContext.asUndetVar(b1), warn , infer);
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha <: T} and {@code alpha == S}
          * perform {@code S <: T} (which could lead to new bounds).
          */
         CROSS_UPPER_EQ() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b1 : uv.getBounds(InferenceBound.UPPER)) {
                     for (Type b2 : uv.getBounds(InferenceBound.EQ)) {
                         isSubtype(inferenceContext.asUndetVar(b2), inferenceContext.asUndetVar(b1), warn, infer);
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha :> S} and {@code alpha == T}
          * perform {@code S <: T} (which could lead to new bounds).
          */
         CROSS_EQ_LOWER() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b1 : uv.getBounds(InferenceBound.EQ)) {
                     for (Type b2 : uv.getBounds(InferenceBound.LOWER)) {
                         isSubtype(inferenceContext.asUndetVar(b2), inferenceContext.asUndetVar(b1), warn, infer);
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha <: P<T>} and
          * {@code alpha <: P<S>} where P is a parameterized type,
          * perform {@code T = S} (which could lead to new bounds).
          */
         CROSS_UPPER_UPPER() {
             @Override
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 List<Type> boundList = uv.getBounds(InferenceBound.UPPER);
                 List<Type> boundListTail = boundList.tail;
                 while (boundList.nonEmpty()) {
                     List<Type> tmpTail = boundListTail;
                     while (tmpTail.nonEmpty()) {
                         Type b1 = boundList.head;
                         Type b2 = tmpTail.head;
                         if (b1 != b2) {
                             Pair<Type, Type> commonSupers = infer.getParameterizedSupers(b1, b2);
                             if (commonSupers != null) {
                                 List<Type> allParamsSuperBound1 = commonSupers.fst.allparams();
                                 List<Type> allParamsSuperBound2 = commonSupers.snd.allparams();
                                 while (allParamsSuperBound1.nonEmpty() && allParamsSuperBound2.nonEmpty()) {
                                     //traverse the list of all params comparing them
                                     if (!allParamsSuperBound1.head.hasTag(WILDCARD) &&
                                         !allParamsSuperBound2.head.hasTag(WILDCARD)) {
                                         isSameType(inferenceContext.asUndetVar(allParamsSuperBound1.head),
                                             inferenceContext.asUndetVar(allParamsSuperBound2.head), infer);
                                     }
                                     allParamsSuperBound1 = allParamsSuperBound1.tail;
                                     allParamsSuperBound2 = allParamsSuperBound2.tail;
                                 }
                                 Assert.check(allParamsSuperBound1.isEmpty() && allParamsSuperBound2.isEmpty());
                             }
                         }
                         tmpTail = tmpTail.tail;
                     }
                     boundList = boundList.tail;
                     boundListTail = boundList.tail;
                 }
             }
             @Override
             boolean accepts(UndetVar uv, InferenceContext inferenceContext) {
                 return !uv.isCaptured() &&
                         uv.getBounds(InferenceBound.UPPER).nonEmpty();
             }
         },
         /**
          * Given a bound set containing {@code alpha == S} and {@code alpha == T}
          * perform {@code S == T} (which could lead to new bounds).
          */
         CROSS_EQ_EQ() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b1 : uv.getBounds(InferenceBound.EQ)) {
                     for (Type b2 : uv.getBounds(InferenceBound.EQ)) {
                         if (b1 != b2) {
                             isSameType(inferenceContext.asUndetVar(b2), inferenceContext.asUndetVar(b1), infer);
                         }
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha <: beta} propagate lower bounds
          * from alpha to beta; also propagate upper bounds from beta to alpha.
          */
         PROP_UPPER() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b : uv.getBounds(InferenceBound.UPPER)) {
                     if (inferenceContext.inferenceVars().contains(b)) {
                         UndetVar uv2 = (UndetVar)inferenceContext.asUndetVar(b);
                         if (uv2.isCaptured()) continue;
                         //alpha <: beta
                         //0. set beta :> alpha
                         addBound(InferenceBound.LOWER, uv2, inferenceContext.asInstType(uv.qtype), infer);
                         //1. copy alpha's lower to beta's
                         for (Type l : uv.getBounds(InferenceBound.LOWER)) {
                             addBound(InferenceBound.LOWER, uv2, inferenceContext.asInstType(l), infer);
                         }
                         //2. copy beta's upper to alpha's
                         for (Type u : uv2.getBounds(InferenceBound.UPPER)) {
                             addBound(InferenceBound.UPPER, uv, inferenceContext.asInstType(u), infer);
                         }
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha :> beta} propagate lower bounds
          * from beta to alpha; also propagate upper bounds from alpha to beta.
          */
         PROP_LOWER() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b : uv.getBounds(InferenceBound.LOWER)) {
                     if (inferenceContext.inferenceVars().contains(b)) {
                         UndetVar uv2 = (UndetVar)inferenceContext.asUndetVar(b);
                         if (uv2.isCaptured()) continue;
                         //alpha :> beta
                         //0. set beta <: alpha
                         addBound(InferenceBound.UPPER, uv2, inferenceContext.asInstType(uv.qtype), infer);
                         //1. copy alpha's upper to beta's
                         for (Type u : uv.getBounds(InferenceBound.UPPER)) {
                             addBound(InferenceBound.UPPER, uv2, inferenceContext.asInstType(u), infer);
                         }
                         //2. copy beta's lower to alpha's
                         for (Type l : uv2.getBounds(InferenceBound.LOWER)) {
                             addBound(InferenceBound.LOWER, uv, inferenceContext.asInstType(l), infer);
                         }
                     }
                 }
             }
         },
         /**
          * Given a bound set containing {@code alpha == beta} propagate lower/upper
          * bounds from alpha to beta and back.
          */
         PROP_EQ() {
             public void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn) {
                 Infer infer = inferenceContext.infer();
                 for (Type b : uv.getBounds(InferenceBound.EQ)) {
                     if (inferenceContext.inferenceVars().contains(b)) {
                         UndetVar uv2 = (UndetVar)inferenceContext.asUndetVar(b);
                         if (uv2.isCaptured()) continue;
                         //alpha == beta
                         //0. set beta == alpha
                         addBound(InferenceBound.EQ, uv2, inferenceContext.asInstType(uv.qtype), infer);
                         //1. copy all alpha's bounds to beta's
                         for (InferenceBound ib : InferenceBound.values()) {
                             for (Type b2 : uv.getBounds(ib)) {
                                 if (b2 != uv2) {
                                     addBound(ib, uv2, inferenceContext.asInstType(b2), infer);
                                 }
                             }
                         }
                         //2. copy all beta's bounds to alpha's
                         for (InferenceBound ib : InferenceBound.values()) {
                             for (Type b2 : uv2.getBounds(ib)) {
                                 if (b2 != uv) {
                                     addBound(ib, uv, inferenceContext.asInstType(b2), infer);
                                 }
                             }
                         }
                     }
                 }
             }
         };
         abstract void apply(UndetVar uv, InferenceContext inferenceContext, Warner warn);
         boolean accepts(UndetVar uv, InferenceContext inferenceContext) {
             return !uv.isCaptured();
         }
         boolean isSubtype(Type s, Type t, Warner warn, Infer infer) {
             return doIncorporationOp(IncorporationBinaryOpKind.IS_SUBTYPE, s, t, warn, infer);
         }
         boolean isSameType(Type s, Type t, Infer infer) {
             return doIncorporationOp(IncorporationBinaryOpKind.IS_SAME_TYPE, s, t, null, infer);
         }
         void addBound(InferenceBound ib, UndetVar uv, Type b, Infer infer) {
             doIncorporationOp(opFor(ib), uv, b, null, infer);
         }
         IncorporationBinaryOpKind opFor(InferenceBound boundKind) {
             switch (boundKind) {
                 case EQ:
                     return IncorporationBinaryOpKind.ADD_EQ_BOUND;
                 case LOWER:
                     return IncorporationBinaryOpKind.ADD_LOWER_BOUND;
                 case UPPER:
                     return IncorporationBinaryOpKind.ADD_UPPER_BOUND;
                 default:
                     Assert.error("Can't get here!");
                     return null;
             }
         }
         boolean doIncorporationOp(IncorporationBinaryOpKind opKind, Type op1, Type op2, Warner warn, Infer infer) {
             IncorporationBinaryOp newOp = infer.new IncorporationBinaryOp(opKind, op1, op2);
             Boolean res = infer.incorporationCache.get(newOp);
             if (res == null) {
                 infer.incorporationCache.put(newOp, res = newOp.apply(warn));
             }
             return res;
         }
     }
     /** incorporation steps to be executed when running in legacy mode */
     EnumSet<IncorporationStep> incorporationStepsLegacy = EnumSet.of(IncorporationStep.EQ_CHECK_LEGACY);
     /** incorporation steps to be executed when running in graph mode */
     EnumSet<IncorporationStep> incorporationStepsGraph =
             EnumSet.complementOf(EnumSet.of(IncorporationStep.EQ_CHECK_LEGACY));
     /**
      * Three kinds of basic operation are supported as part of an incorporation step:
      * (i) subtype check, (ii) same type check and (iii) bound addition (either
      * upper/lower/eq bound).
      */
     enum IncorporationBinaryOpKind {
         IS_SUBTYPE() {
             @Override
             boolean apply(Type op1, Type op2, Warner warn, Types types) {
                 return types.isSubtypeUnchecked(op1, op2, warn);
             }
         },
         IS_SAME_TYPE() {
             @Override
             boolean apply(Type op1, Type op2, Warner warn, Types types) {
                 return types.isSameType(op1, op2);
             }
         },
         ADD_UPPER_BOUND() {
             @Override
             boolean apply(Type op1, Type op2, Warner warn, Types types) {
                 UndetVar uv = (UndetVar)op1;
                 uv.addBound(InferenceBound.UPPER, op2, types);
                 return true;
             }
         },
         ADD_LOWER_BOUND() {
             @Override
             boolean apply(Type op1, Type op2, Warner warn, Types types) {
                 UndetVar uv = (UndetVar)op1;
                 uv.addBound(InferenceBound.LOWER, op2, types);
                 return true;
             }
         },
         ADD_EQ_BOUND() {
             @Override
             boolean apply(Type op1, Type op2, Warner warn, Types types) {
                 UndetVar uv = (UndetVar)op1;
                 uv.addBound(InferenceBound.EQ, op2, types);
                 return true;
             }
         };
         abstract boolean apply(Type op1, Type op2, Warner warn, Types types);
     }
     /**
      * This class encapsulates a basic incorporation operation; incorporation
      * operations takes two type operands and a kind. Each operation performed
      * during an incorporation round is stored in a cache, so that operations
      * are not executed unnecessarily (which would potentially lead to adding
      * same bounds over and over).
      */
     class IncorporationBinaryOp {
         IncorporationBinaryOpKind opKind;
         Type op1;
         Type op2;
         IncorporationBinaryOp(IncorporationBinaryOpKind opKind, Type op1, Type op2) {
             this.opKind = opKind;
             this.op1 = op1;
             this.op2 = op2;
         }
         @Override
         public boolean equals(Object o) {
             if (!(o instanceof IncorporationBinaryOp)) {
                 return false;
             } else {
                 IncorporationBinaryOp that = (IncorporationBinaryOp)o;
                 return opKind == that.opKind &&
                         types.isSameType(op1, that.op1, true) &&
                         types.isSameType(op2, that.op2, true);
             }
         }
         @Override
         public int hashCode() {
             int result = opKind.hashCode();
             result *= 127;
             result += types.hashCode(op1);
             result *= 127;
             result += types.hashCode(op2);
             return result;
         }
         boolean apply(Warner warn) {
             return opKind.apply(op1, op2, warn, types);
         }
     }
     /** an incorporation cache keeps track of all executed incorporation-related operations */
     Map<IncorporationBinaryOp, Boolean> incorporationCache =
             new HashMap<IncorporationBinaryOp, Boolean>();
     /**
      * Make sure that the upper bounds we got so far lead to a solvable inference
      * variable by making sure that a glb exists.
      */
     void checkCompatibleUpperBounds(UndetVar uv, InferenceContext inferenceContext) {
         List<Type> hibounds =
                 Type.filter(uv.getBounds(InferenceBound.UPPER), new BoundFilter(inferenceContext));
         Type hb = null;
         if (hibounds.isEmpty())
             hb = syms.objectType;
         else if (hibounds.tail.isEmpty())
             hb = hibounds.head;
         else
             hb = types.glb(hibounds);
         if (hb == null || hb.isErroneous())
             reportBoundError(uv, BoundErrorKind.BAD_UPPER);
     }
     //where
         protected static class BoundFilter implements Filter<Type> {
             InferenceContext inferenceContext;
             public BoundFilter(InferenceContext inferenceContext) {
                 this.inferenceContext = inferenceContext;
             }
             @Override
             public boolean accepts(Type t) {
                 return !t.isErroneous() && !inferenceContext.free(t) &&
                         !t.hasTag(BOT);
             }
         };
     /**
      * This enumeration defines all possible bound-checking related errors.
      */
     enum BoundErrorKind {
         /**
          * The (uninstantiated) inference variable has incompatible upper bounds.
          */
         BAD_UPPER() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("incompatible.upper.bounds", uv.qtype,
                         uv.getBounds(InferenceBound.UPPER));
             }
         },
         /**
          * An equality constraint is not compatible with an upper bound.
          */
         BAD_EQ_UPPER() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("incompatible.eq.upper.bounds", uv.qtype,
                         uv.getBounds(InferenceBound.EQ), uv.getBounds(InferenceBound.UPPER));
             }
         },
         /**
          * An equality constraint is not compatible with a lower bound.
          */
         BAD_EQ_LOWER() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("incompatible.eq.lower.bounds", uv.qtype,
                         uv.getBounds(InferenceBound.EQ), uv.getBounds(InferenceBound.LOWER));
             }
         },
         /**
          * Instantiated inference variable is not compatible with an upper bound.
          */
         UPPER() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("inferred.do.not.conform.to.upper.bounds", uv.inst,
                         uv.getBounds(InferenceBound.UPPER));
             }
         },
         /**
          * Instantiated inference variable is not compatible with a lower bound.
          */
         LOWER() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("inferred.do.not.conform.to.lower.bounds", uv.inst,
                         uv.getBounds(InferenceBound.LOWER));
             }
         },
         /**
          * Instantiated inference variable is not compatible with an equality constraint.
          */
         EQ() {
             @Override
             InapplicableMethodException setMessage(InferenceException ex, UndetVar uv) {
                 return ex.setMessage("inferred.do.not.conform.to.eq.bounds", uv.inst,
                         uv.getBounds(InferenceBound.EQ));
             }
         };
         abstract InapplicableMethodException setMessage(InferenceException ex, UndetVar uv);
     }
     /**
      * Report a bound-checking error of given kind
      */
     void reportBoundError(UndetVar uv, BoundErrorKind bk) {
         throw bk.setMessage(inferenceException, uv);
     }
     // </editor-fold>
     // <editor-fold defaultstate="collapsed" desc="Inference engine">
     /**
      * Graph inference strategy - act as an input to the inference solver; a strategy is
      * composed of two ingredients: (i) find a node to solve in the inference graph,
      * and (ii) tell th engine when we are done fixing inference variables
      */
     interface GraphStrategy {
         /**
          * A NodeNotFoundException is thrown whenever an inference strategy fails
          * to pick the next node to solve in the inference graph.
          */
         public static class NodeNotFoundException extends RuntimeException {
             private static final long serialVersionUID = 0;
             InferenceGraph graph;
             public NodeNotFoundException(InferenceGraph graph) {
                 this.graph = graph;
             }
         }
         /**
          * Pick the next node (leaf) to solve in the graph
          */
         Node pickNode(InferenceGraph g) throws NodeNotFoundException;
         /**
          * Is this the last step?
          */
         boolean done();
     }
     /**
      * Simple solver strategy class that locates all leaves inside a graph
      * and picks the first leaf as the next node to solve
      */
     abstract class LeafSolver implements GraphStrategy {
         public Node pickNode(InferenceGraph g) {
             if (g.nodes.isEmpty()) {
                 //should not happen
                 throw new NodeNotFoundException(g);
             };
             return g.nodes.get(0);
         }
         boolean isSubtype(Type s, Type t, Warner warn, Infer infer) {
             return doIncorporationOp(IncorporationBinaryOpKind.IS_SUBTYPE, s, t, warn, infer);
         }
         boolean isSameType(Type s, Type t, Infer infer) {
             return doIncorporationOp(IncorporationBinaryOpKind.IS_SAME_TYPE, s, t, null, infer);
         }
         void addBound(InferenceBound ib, UndetVar uv, Type b, Infer infer) {
             doIncorporationOp(opFor(ib), uv, b, null, infer);
         }
         IncorporationBinaryOpKind opFor(InferenceBound boundKind) {
             switch (boundKind) {
                 case EQ:
                     return IncorporationBinaryOpKind.ADD_EQ_BOUND;
                 case LOWER:
                     return IncorporationBinaryOpKind.ADD_LOWER_BOUND;
                 case UPPER:
                     return IncorporationBinaryOpKind.ADD_UPPER_BOUND;
                 default:
                     Assert.error("Can't get here!");
                     return null;
             }
         }
         boolean doIncorporationOp(IncorporationBinaryOpKind opKind, Type op1, Type op2, Warner warn, Infer infer) {
             IncorporationBinaryOp newOp = infer.new IncorporationBinaryOp(opKind, op1, op2);
             Boolean res = infer.incorporationCache.get(newOp);
             if (res == null) {
                 infer.incorporationCache.put(newOp, res = newOp.apply(warn));
             }
             return res;
         }
     }
     /**
      * This solver uses an heuristic to pick the best leaf - the heuristic
      * tries to select the node that has maximal probability to contain one
      * or more inference variables in a given list
      */
     abstract class BestLeafSolver extends LeafSolver {
         /** list of ivars of which at least one must be solved */
         List<Type> varsToSolve;
         BestLeafSolver(List<Type> varsToSolve) {
             this.varsToSolve = varsToSolve;
         }
         /**
          * Computes a path that goes from a given node to the leafs in the graph.
          * Typically this will start from a node containing a variable in
          * {@code varsToSolve}. For any given path, the cost is computed as the total
          * number of type-variables that should be eagerly instantiated across that path.
          */
         Pair<List<Node>, Integer> computeTreeToLeafs(Node n) {
             Pair<List<Node>, Integer> cachedPath = treeCache.get(n);
             if (cachedPath == null) {
                 //cache miss
                 if (n.isLeaf()) {
                     //if leaf, stop
                     cachedPath = new Pair<List<Node>, Integer>(List.of(n), n.data.length());
                 } else {
                     //if non-leaf, proceed recursively
                     Pair<List<Node>, Integer> path = new Pair<List<Node>, Integer>(List.of(n), n.data.length());
                     for (Node n2 : n.getAllDependencies()) {
                         if (n2 == n) continue;
                         Pair<List<Node>, Integer> subpath = computeTreeToLeafs(n2);
                         path = new Pair<List<Node>, Integer>(
                                 path.fst.prependList(subpath.fst),
                                 path.snd + subpath.snd);
                     }
                     cachedPath = path;
                 }
                 //save results in cache
                 treeCache.put(n, cachedPath);
             }
             return cachedPath;
         }
         /** cache used to avoid redundant computation of tree costs */
         final Map<Node, Pair<List<Node>, Integer>> treeCache =
                 new HashMap<Node, Pair<List<Node>, Integer>>();
         /** constant value used to mark non-existent paths */
         final Pair<List<Node>, Integer> noPath =
                 new Pair<List<Node>, Integer>(null, Integer.MAX_VALUE);
         /**
          * Pick the leaf that minimize cost
          */
         @Override
         public Node pickNode(final InferenceGraph g) {
             treeCache.clear(); //graph changes at every step - cache must be cleared
             Pair<List<Node>, Integer> bestPath = noPath;
             for (Node n : g.nodes) {
                 if (!Collections.disjoint(n.data, varsToSolve)) {
                     Pair<List<Node>, Integer> path = computeTreeToLeafs(n);
                     //discard all paths containing at least a node in the
                     //closure computed above
                     if (path.snd < bestPath.snd) {
                         bestPath = path;
                     }
                 }
             }
             if (bestPath == noPath) {
                 //no path leads there
                 throw new NodeNotFoundException(g);
             }
             return bestPath.fst.head;
         }
     }
     /**
      * The inference process can be thought of as a sequence of steps. Each step
      * instantiates an inference variable using a subset of the inference variable
      * bounds, if certain condition are met. Decisions such as the sequence in which
      * steps are applied, or which steps are to be applied are left to the inference engine.
      */
     enum InferenceStep {
         /**
          * Instantiate an inference variables using one of its (ground) equality
          * constraints
          */
         EQ(InferenceBound.EQ) {
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 return filterBounds(uv, inferenceContext).head;
             }
         },
         /**
          * Instantiate an inference variables using its (ground) lower bounds. Such
          * bounds are merged together using lub().
          */
         LOWER(InferenceBound.LOWER) {
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 Infer infer = inferenceContext.infer();
                 List<Type> lobounds = filterBounds(uv, inferenceContext);
                 //note: lobounds should have at least one element
                 Type owntype = lobounds.tail.tail == null  ? lobounds.head : infer.types.lub(lobounds);
                 if (owntype.isPrimitive() || owntype.hasTag(ERROR)) {
                     throw infer.inferenceException
                         .setMessage("no.unique.minimal.instance.exists",
                                     uv.qtype, lobounds);
                 } else {
                     return owntype;
                 }
             }
         },
         /**
          * Infer uninstantiated/unbound inference variables occurring in 'throws'
          * clause as RuntimeException
          */
         THROWS(InferenceBound.UPPER) {
             @Override
             public boolean accepts(UndetVar t, InferenceContext inferenceContext) {
                 if ((t.qtype.tsym.flags() & Flags.THROWS) == 0) {
                     //not a throws undet var
                     return false;
                 }
                 if (t.getBounds(InferenceBound.EQ, InferenceBound.LOWER, InferenceBound.UPPER)
                             .diff(t.getDeclaredBounds()).nonEmpty()) {
                     //not an unbounded undet var
                     return false;
                 }
                 Infer infer = inferenceContext.infer();
                 for (Type db : t.getDeclaredBounds()) {
                     if (t.isInterface()) continue;
                     if (infer.types.asSuper(infer.syms.runtimeExceptionType, db.tsym) != null) {
                         //declared bound is a supertype of RuntimeException
                         return true;
                     }
                 }
                 //declared bound is more specific then RuntimeException - give up
                 return false;
             }
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 return inferenceContext.infer().syms.runtimeExceptionType;
             }
         },
         /**
          * Instantiate an inference variables using its (ground) upper bounds. Such
          * bounds are merged together using glb().
          */
         UPPER(InferenceBound.UPPER) {
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 Infer infer = inferenceContext.infer();
                 List<Type> hibounds = filterBounds(uv, inferenceContext);
                 //note: hibounds should have at least one element
                 Type owntype = hibounds.tail.tail == null  ? hibounds.head : infer.types.glb(hibounds);
                 if (owntype.isPrimitive() || owntype.hasTag(ERROR)) {
                     throw infer.inferenceException
                         .setMessage("no.unique.maximal.instance.exists",
                                     uv.qtype, hibounds);
                 } else {
                     return owntype;
                 }
             }
         },
         /**
          * Like the former; the only difference is that this step can only be applied
          * if all upper bounds are ground.
          */
         UPPER_LEGACY(InferenceBound.UPPER) {
             @Override
             public boolean accepts(UndetVar t, InferenceContext inferenceContext) {
                 return !inferenceContext.free(t.getBounds(ib)) && !t.isCaptured();
             }
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 return UPPER.solve(uv, inferenceContext);
             }
         },
         /**
          * Like the former; the only difference is that this step can only be applied
          * if all upper/lower bounds are ground.
          */
         CAPTURED(InferenceBound.UPPER) {
             @Override
             public boolean accepts(UndetVar t, InferenceContext inferenceContext) {
                 return t.isCaptured() &&
                         !inferenceContext.free(t.getBounds(InferenceBound.UPPER, InferenceBound.LOWER));
             }
             @Override
             Type solve(UndetVar uv, InferenceContext inferenceContext) {
                 Infer infer = inferenceContext.infer();
                 Type upper = UPPER.filterBounds(uv, inferenceContext).nonEmpty() ?
                         UPPER.solve(uv, inferenceContext) :
                         infer.syms.objectType;
                 Type lower = LOWER.filterBounds(uv, inferenceContext).nonEmpty() ?
                         LOWER.solve(uv, inferenceContext) :
                         infer.syms.botType;
                 CapturedType prevCaptured = (CapturedType)uv.qtype;
                 return new CapturedType(prevCaptured.tsym.name, prevCaptured.tsym.owner, upper, lower, prevCaptured.wildcard);
             }
         };
         final InferenceBound ib;
         InferenceStep(InferenceBound ib) {
             this.ib = ib;
         }
         /**
          * Find an instantiated type for a given inference variable within
          * a given inference context
          */
         abstract Type solve(UndetVar uv, InferenceContext inferenceContext);
         /**
          * Can the inference variable be instantiated using this step?
          */
         public boolean accepts(UndetVar t, InferenceContext inferenceContext) {
             return filterBounds(t, inferenceContext).nonEmpty() && !t.isCaptured();
         }
         /**
          * Return the subset of ground bounds in a given bound set (i.e. eq/lower/upper)
          */
         List<Type> filterBounds(UndetVar uv, InferenceContext inferenceContext) {
             return Type.filter(uv.getBounds(ib), new BoundFilter(inferenceContext));
         }
     }
     /**
      * This enumeration defines the sequence of steps to be applied when the
      * solver works in legacy mode. The steps in this enumeration reflect
      * the behavior of old inference routine (see JLS SE 7 15.12.2.7/15.12.2.8).
      */
     enum LegacyInferenceSteps {
         EQ_LOWER(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER)),
         EQ_UPPER(EnumSet.of(InferenceStep.EQ, InferenceStep.UPPER_LEGACY));
         final EnumSet<InferenceStep> steps;
         LegacyInferenceSteps(EnumSet<InferenceStep> steps) {
             this.steps = steps;
         }
     }
     /**
      * This enumeration defines the sequence of steps to be applied when the
      * graph solver is used. This order is defined so as to maximize compatibility
      * w.r.t. old inference routine (see JLS SE 7 15.12.2.7/15.12.2.8).
      */
     enum GraphInferenceSteps {
         EQ(EnumSet.of(InferenceStep.EQ)),
         EQ_LOWER(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER)),
         EQ_LOWER_THROWS_UPPER_CAPTURED(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER, InferenceStep.UPPER, InferenceStep.THROWS, InferenceStep.CAPTURED));
         final EnumSet<InferenceStep> steps;
         GraphInferenceSteps(EnumSet<InferenceStep> steps) {
             this.steps = steps;
         }
     }
     /**
      * There are two kinds of dependencies between inference variables. The basic
      * kind of dependency (or bound dependency) arises when a variable mention
      * another variable in one of its bounds. There's also a more subtle kind
      * of dependency that arises when a variable 'might' lead to better constraints
      * on another variable (this is typically the case with variables holding up
      * stuck expressions).
      */
     enum DependencyKind implements GraphUtils.DependencyKind {
         /** bound dependency */
         BOUND("dotted"),
         /** stuck dependency */
         STUCK("dashed");
         final String dotSyle;
         private DependencyKind(String dotSyle) {
             this.dotSyle = dotSyle;
         }
         @Override
         public String getDotStyle() {
             return dotSyle;
         }
     }
     /**
      * This is the graph inference solver - the solver organizes all inference variables in
      * a given inference context by bound dependencies - in the general case, such dependencies
      * would lead to a cyclic directed graph (hence the name); the dependency info is used to build
      * an acyclic graph, where all cyclic variables are bundled together. An inference
      * step corresponds to solving a node in the acyclic graph - this is done by
      * relying on a given strategy (see GraphStrategy).
      */
     class GraphSolver {
         InferenceContext inferenceContext;
         Map<Type, Set<Type>> stuckDeps;
         Warner warn;
         GraphSolver(InferenceContext inferenceContext, Map<Type, Set<Type>> stuckDeps, Warner warn) {
             this.inferenceContext = inferenceContext;
             this.stuckDeps = stuckDeps;
             this.warn = warn;
         }
         /**
          * Solve variables in a given inference context. The amount of variables
          * to be solved, and the way in which the underlying acyclic graph is explored
          * depends on the selected solver strategy.
          */
         void solve(GraphStrategy sstrategy) {
             checkWithinBounds(inferenceContext, warn); //initial propagation of bounds
             InferenceGraph inferenceGraph = new InferenceGraph(stuckDeps);
             while (!sstrategy.done()) {
                 InferenceGraph.Node nodeToSolve = sstrategy.pickNode(inferenceGraph);
                 List<Type> varsToSolve = List.from(nodeToSolve.data);
                 List<Type> saved_undet = inferenceContext.save();
                 try {
                     //repeat until all variables are solved
                     outer: while (Type.containsAny(inferenceContext.restvars(), varsToSolve)) {
                         //for each inference phase
                         for (GraphInferenceSteps step : GraphInferenceSteps.values()) {
                             if (inferenceContext.solveBasic(varsToSolve, step.steps)) {
                                 checkWithinBounds(inferenceContext, warn);
                                 continue outer;
                             }
                         }
                         //no progress
                         throw inferenceException.setMessage();
                     }
                 }
                 catch (InferenceException ex) {
                     //did we fail because of interdependent ivars?
                     inferenceContext.rollback(saved_undet);
                     instantiateAsUninferredVars(varsToSolve, inferenceContext);
                     checkWithinBounds(inferenceContext, warn);
                 }
                 inferenceGraph.deleteNode(nodeToSolve);
             }
         }
         /**
          * The dependencies between the inference variables that need to be solved
          * form a (possibly cyclic) graph. This class reduces the original dependency graph
          * to an acyclic version, where cyclic nodes are folded into a single 'super node'.
          */
         class InferenceGraph {
             /**
              * This class represents a node in the graph. Each node corresponds
              * to an inference variable and has edges (dependencies) on other
              * nodes. The node defines an entry point that can be used to receive
              * updates on the structure of the graph this node belongs to (used to
              * keep dependencies in sync).
              */
             class Node extends GraphUtils.TarjanNode<ListBuffer<Type>> {
                 /** map listing all dependencies (grouped by kind) */
                 EnumMap<DependencyKind, Set<Node>> deps;
                 Node(Type ivar) {
                     super(ListBuffer.of(ivar));
                     this.deps = new EnumMap<DependencyKind, Set<Node>>(DependencyKind.class);
                 }
                 @Override
                 public GraphUtils.DependencyKind[] getSupportedDependencyKinds() {
                     return DependencyKind.values();
                 }
                 @Override
                 public String getDependencyName(GraphUtils.Node<ListBuffer<Type>> to, GraphUtils.DependencyKind dk) {
                     if (dk == DependencyKind.STUCK) return "";
                     else {
                         StringBuilder buf = new StringBuilder();
                         String sep = "";
                         for (Type from : data) {
                             UndetVar uv = (UndetVar)inferenceContext.asUndetVar(from);
                             for (Type bound : uv.getBounds(InferenceBound.values())) {
                                 if (bound.containsAny(List.from(to.data))) {
                                     buf.append(sep);
                                     buf.append(bound);
                                     sep = ",";
                                 }
                             }
                         }
                         return buf.toString();
                     }
                 }
                 @Override
                 public Iterable<? extends Node> getAllDependencies() {
                     return getDependencies(DependencyKind.values());
                 }
                 @Override
                 public Iterable<? extends TarjanNode<ListBuffer<Type>>> getDependenciesByKind(GraphUtils.DependencyKind dk) {
                     return getDependencies((DependencyKind)dk);
                 }
                 /**
                  * Retrieves all dependencies with given kind(s).
                  */
                 protected Set<Node> getDependencies(DependencyKind... depKinds) {
                     Set<Node> buf = new LinkedHashSet<Node>();
                     for (DependencyKind dk : depKinds) {
                         Set<Node> depsByKind = deps.get(dk);
                         if (depsByKind != null) {
                             buf.addAll(depsByKind);
                         }
                     }
                     return buf;
                 }
                 /**
                  * Adds dependency with given kind.
                  */
                 protected void addDependency(DependencyKind dk, Node depToAdd) {
                     Set<Node> depsByKind = deps.get(dk);
                     if (depsByKind == null) {
                         depsByKind = new LinkedHashSet<Node>();
                         deps.put(dk, depsByKind);
                     }
                     depsByKind.add(depToAdd);
                 }
                 /**
                  * Add multiple dependencies of same given kind.
                  */
                 protected void addDependencies(DependencyKind dk, Set<Node> depsToAdd) {
                     for (Node n : depsToAdd) {
                         addDependency(dk, n);
                     }
                 }
                 /**
                  * Remove a dependency, regardless of its kind.
                  */
                 protected Set<DependencyKind> removeDependency(Node n) {
                     Set<DependencyKind> removedKinds = new HashSet<>();
                     for (DependencyKind dk : DependencyKind.values()) {
                         Set<Node> depsByKind = deps.get(dk);
                         if (depsByKind == null) continue;
                         if (depsByKind.remove(n)) {
                             removedKinds.add(dk);
                         }
                     }
                     return removedKinds;
                 }
                 /**
                  * Compute closure of a give node, by recursively walking
                  * through all its dependencies (of given kinds)
                  */
                 protected Set<Node> closure(DependencyKind... depKinds) {
                     boolean progress = true;
                     Set<Node> closure = new HashSet<Node>();
                     closure.add(this);
                     while (progress) {
                         progress = false;
                         for (Node n1 : new HashSet<Node>(closure)) {
                             progress = closure.addAll(n1.getDependencies(depKinds));
                         }
                     }
                     return closure;
                 }
                 /**
                  * Is this node a leaf? This means either the node has no dependencies,
                  * or it just has self-dependencies.
                  */
                 protected boolean isLeaf() {
                     //no deps, or only one self dep
                     Set<Node> allDeps = getDependencies(DependencyKind.BOUND, DependencyKind.STUCK);
                     if (allDeps.isEmpty()) return true;
                     for (Node n : allDeps) {
                         if (n != this) {
                             return false;
                         }
                     }
                     return true;
                 }
                 /**
                  * Merge this node with another node, acquiring its dependencies.
                  * This routine is used to merge all cyclic node together and
                  * form an acyclic graph.
                  */
                 protected void mergeWith(List<? extends Node> nodes) {
                     for (Node n : nodes) {
                         Assert.check(n.data.length() == 1, "Attempt to merge a compound node!");
                         data.appendList(n.data);
                         for (DependencyKind dk : DependencyKind.values()) {
                             addDependencies(dk, n.getDependencies(dk));
                         }
                     }
                     //update deps
                     EnumMap<DependencyKind, Set<Node>> deps2 = new EnumMap<DependencyKind, Set<Node>>(DependencyKind.class);
                     for (DependencyKind dk : DependencyKind.values()) {
                         for (Node d : getDependencies(dk)) {
                             Set<Node> depsByKind = deps2.get(dk);
                             if (depsByKind == null) {
                                 depsByKind = new LinkedHashSet<Node>();
                                 deps2.put(dk, depsByKind);
                             }
                             if (data.contains(d.data.first())) {
                                 depsByKind.add(this);
                             } else {
                                 depsByKind.add(d);
                             }
                         }
                     }
                     deps = deps2;
                 }
                 /**
                  * Notify all nodes that something has changed in the graph
                  * topology.
                  */
                 private void graphChanged(Node from, Node to) {
                     for (DependencyKind dk : removeDependency(from)) {
                         if (to != null) {
                             addDependency(dk, to);
                         }
                     }
                 }
             }
             /** the nodes in the inference graph */
             ArrayList<Node> nodes;
             InferenceGraph(Map<Type, Set<Type>> optDeps) {
                 initNodes(optDeps);
             }
             /**
              * Basic lookup helper for retrieving a graph node given an inference
              * variable type.
              */
             public Node findNode(Type t) {
                 for (Node n : nodes) {
                     if (n.data.contains(t)) {
                         return n;
                     }
                 }
                 return null;
             }
             /**
              * Delete a node from the graph. This update the underlying structure
              * of the graph (including dependencies) via listeners updates.
              */
             public void deleteNode(Node n) {
                 Assert.check(nodes.contains(n));
                 nodes.remove(n);
                 notifyUpdate(n, null);
             }
             /**
              * Notify all nodes of a change in the graph. If the target node is
              * {@code null} the source node is assumed to be removed.
              */
             void notifyUpdate(Node from, Node to) {
                 for (Node n : nodes) {
                     n.graphChanged(from, to);
                 }
             }
             /**
              * Create the graph nodes. First a simple node is created for every inference
              * variables to be solved. Then Tarjan is used to found all connected components
              * in the graph. For each component containing more than one node, a super node is
              * created, effectively replacing the original cyclic nodes.
              */
             void initNodes(Map<Type, Set<Type>> stuckDeps) {
                 //add nodes
                 nodes = new ArrayList<Node>();
                 for (Type t : inferenceContext.restvars()) {
                     nodes.add(new Node(t));
                 }
                 //add dependencies
                 for (Node n_i : nodes) {
                     Type i = n_i.data.first();
                     Set<Type> optDepsByNode = stuckDeps.get(i);
                     for (Node n_j : nodes) {
                         Type j = n_j.data.first();
                         UndetVar uv_i = (UndetVar)inferenceContext.asUndetVar(i);
                         if (Type.containsAny(uv_i.getBounds(InferenceBound.values()), List.of(j))) {
                             //update i's bound dependencies
                             n_i.addDependency(DependencyKind.BOUND, n_j);
                         }
                         if (optDepsByNode != null && optDepsByNode.contains(j)) {
                             //update i's stuck dependencies
                             n_i.addDependency(DependencyKind.STUCK, n_j);
                         }
                     }
                 }
                 //merge cyclic nodes
                 ArrayList<Node> acyclicNodes = new ArrayList<Node>();
                 for (List<? extends Node> conSubGraph : GraphUtils.tarjan(nodes)) {
                     if (conSubGraph.length() > 1) {
                         Node root = conSubGraph.head;
                         root.mergeWith(conSubGraph.tail);
                         for (Node n : conSubGraph) {
                             notifyUpdate(n, root);
                         }
                     }
                     acyclicNodes.add(conSubGraph.head);
                 }
                 nodes = acyclicNodes;
             }
             /**
              * Debugging: dot representation of this graph
              */
             String toDot() {
                 StringBuilder buf = new StringBuilder();
                 for (Type t : inferenceContext.undetvars) {
                     UndetVar uv = (UndetVar)t;
                     buf.append(String.format("var %s - upper bounds = %s, lower bounds = %s, eq bounds = %s\\n",
                             uv.qtype, uv.getBounds(InferenceBound.UPPER), uv.getBounds(InferenceBound.LOWER),
                             uv.getBounds(InferenceBound.EQ)));
                 }
                 return GraphUtils.toDot(nodes, "inferenceGraph" + hashCode(), buf.toString());
             }
         }
     }
     // </editor-fold>
     // <editor-fold defaultstate="collapsed" desc="Inference context">
     /**
      * Functional interface for defining inference callbacks. Certain actions
      * (i.e. subtyping checks) might need to be redone after all inference variables
      * have been fixed.
      */
     interface FreeTypeListener {
         void typesInferred(InferenceContext inferenceContext);
     }
     /**
      * An inference context keeps track of the set of variables that are free
      * in the current context. It provides utility methods for opening/closing
      * types to their corresponding free/closed forms. It also provide hooks for
      * attaching deferred post-inference action (see PendingCheck). Finally,
      * it can be used as an entry point for performing upper/lower bound inference
      * (see InferenceKind).
      */
      class InferenceContext {
         /** list of inference vars as undet vars */
         List<Type> undetvars;
         /** list of inference vars in this context */
         List<Type> inferencevars;
         java.util.Map<FreeTypeListener, List<Type>> freeTypeListeners =
                 new java.util.HashMap<FreeTypeListener, List<Type>>();
         List<FreeTypeListener> freetypeListeners = List.nil();
         public InferenceContext(List<Type> inferencevars) {
             this.undetvars = Type.map(inferencevars, fromTypeVarFun);
             this.inferencevars = inferencevars;
         }
         //where
             Mapping fromTypeVarFun = new Mapping("fromTypeVarFunWithBounds") {
                 // mapping that turns inference variables into undet vars
                 public Type apply(Type t) {
                     if (t.hasTag(TYPEVAR)) {
                         TypeVar tv = (TypeVar)t;
                         if (tv.isCaptured()) {
                             return new CapturedUndetVar((CapturedType)tv, types);
                         } else {
                             return new UndetVar(tv, types);
                         }
                     } else {
                         return t.map(this);
                     }
                 }
             };
         /**
          * add a new inference var to this inference context
          */
         void addVar(TypeVar t) {
             this.undetvars = this.undetvars.prepend(fromTypeVarFun.apply(t));
             this.inferencevars = this.inferencevars.prepend(t);
         }
         /**
          * returns the list of free variables (as type-variables) in this
          * inference context
          */
         List<Type> inferenceVars() {
             return inferencevars;
         }
         /**
          * returns the list of uninstantiated variables (as type-variables) in this
          * inference context
          */
         List<Type> restvars() {
             return filterVars(new Filter<UndetVar>() {
                 public boolean accepts(UndetVar uv) {
                     return uv.inst == null;
                 }
             });
         }
         /**
          * returns the list of instantiated variables (as type-variables) in this
          * inference context
          */
         List<Type> instvars() {
             return filterVars(new Filter<UndetVar>() {
                 public boolean accepts(UndetVar uv) {
                     return uv.inst != null;
                 }
             });
         }
         /**
          * Get list of bounded inference variables (where bound is other than
          * declared bounds).
          */
         final List<Type> boundedVars() {
             return filterVars(new Filter<UndetVar>() {
                 public boolean accepts(UndetVar uv) {
                     return uv.getBounds(InferenceBound.UPPER)
                              .diff(uv.getDeclaredBounds())
                              .appendList(uv.getBounds(InferenceBound.EQ, InferenceBound.LOWER)).nonEmpty();
                 }
             });
         }
         /* Returns the corresponding inference variables.
          */
         private List<Type> filterVars(Filter<UndetVar> fu) {
             ListBuffer<Type> res = new ListBuffer<>();
             for (Type t : undetvars) {
                 UndetVar uv = (UndetVar)t;
                 if (fu.accepts(uv)) {
                     res.append(uv.qtype);
                 }
             }
             return res.toList();
         }
         /**
          * is this type free?
          */
         final boolean free(Type t) {
             return t.containsAny(inferencevars);
         }
         final boolean free(List<Type> ts) {
             for (Type t : ts) {
                 if (free(t)) return true;
             }
             return false;
         }
         /**
          * Returns a list of free variables in a given type
          */
         final List<Type> freeVarsIn(Type t) {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type iv : inferenceVars()) {
                 if (t.contains(iv)) {
                     buf.add(iv);
                 }
             }
             return buf.toList();
         }
         final List<Type> freeVarsIn(List<Type> ts) {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type t : ts) {
                 buf.appendList(freeVarsIn(t));
             }
             ListBuffer<Type> buf2 = new ListBuffer<>();
             for (Type t : buf) {
                 if (!buf2.contains(t)) {
                     buf2.add(t);
                 }
             }
             return buf2.toList();
         }
         /**
          * Replace all free variables in a given type with corresponding
          * undet vars (used ahead of subtyping/compatibility checks to allow propagation
          * of inference constraints).
          */
         final Type asUndetVar(Type t) {
             return types.subst(t, inferencevars, undetvars);
         }
         final List<Type> asUndetVars(List<Type> ts) {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type t : ts) {
                 buf.append(asUndetVar(t));
             }
             return buf.toList();
         }
         List<Type> instTypes() {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type t : undetvars) {
                 UndetVar uv = (UndetVar)t;
                 buf.append(uv.inst != null ? uv.inst : uv.qtype);
             }
             return buf.toList();
         }
         /**
          * Replace all free variables in a given type with corresponding
          * instantiated types - if one or more free variable has not been
          * fully instantiated, it will still be available in the resulting type.
          */
         Type asInstType(Type t) {
             return types.subst(t, inferencevars, instTypes());
         }
         List<Type> asInstTypes(List<Type> ts) {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type t : ts) {
                 buf.append(asInstType(t));
             }
             return buf.toList();
         }
         /**
          * Add custom hook for performing post-inference action
          */
         void addFreeTypeListener(List<Type> types, FreeTypeListener ftl) {
             freeTypeListeners.put(ftl, freeVarsIn(types));
         }
         /**
          * Mark the inference context as complete and trigger evaluation
          * of all deferred checks.
          */
         void notifyChange() {
             notifyChange(inferencevars.diff(restvars()));
         }
         void notifyChange(List<Type> inferredVars) {
             InferenceException thrownEx = null;
             for (Map.Entry<FreeTypeListener, List<Type>> entry :
                     new HashMap<FreeTypeListener, List<Type>>(freeTypeListeners).entrySet()) {
                 if (!Type.containsAny(entry.getValue(), inferencevars.diff(inferredVars))) {
                     try {
                         entry.getKey().typesInferred(this);
                         freeTypeListeners.remove(entry.getKey());
                     } catch (InferenceException ex) {
                         if (thrownEx == null) {
                             thrownEx = ex;
                         }
                     }
                 }
             }
             //inference exception multiplexing - present any inference exception
             //thrown when processing listeners as a single one
             if (thrownEx != null) {
                 throw thrownEx;
             }
         }
         /**
          * Save the state of this inference context
          */
         List<Type> save() {
             ListBuffer<Type> buf = new ListBuffer<>();
             for (Type t : undetvars) {
                 UndetVar uv = (UndetVar)t;
                 UndetVar uv2 = new UndetVar((TypeVar)uv.qtype, types);
                 for (InferenceBound ib : InferenceBound.values()) {
                     for (Type b : uv.getBounds(ib)) {
                         uv2.addBound(ib, b, types);
                     }
                 }
                 uv2.inst = uv.inst;
                 buf.add(uv2);
             }
             return buf.toList();
         }
         /**
          * Restore the state of this inference context to the previous known checkpoint
          */
         void rollback(List<Type> saved_undet) {
              Assert.check(saved_undet != null && saved_undet.length() == undetvars.length());
             //restore bounds (note: we need to preserve the old instances)
             for (Type t : undetvars) {
                 UndetVar uv = (UndetVar)t;
                 UndetVar uv_saved = (UndetVar)saved_undet.head;
                 for (InferenceBound ib : InferenceBound.values()) {
                     uv.setBounds(ib, uv_saved.getBounds(ib));
                 }
                 uv.inst = uv_saved.inst;
                 saved_undet = saved_undet.tail;
             }
         }
         /**
          * Copy variable in this inference context to the given context
          */
         void dupTo(final InferenceContext that) {
             that.inferencevars = that.inferencevars.appendList(
                     inferencevars.diff(that.inferencevars));
             that.undetvars = that.undetvars.appendList(
                     undetvars.diff(that.undetvars));
             //set up listeners to notify original inference contexts as
             //propagated vars are inferred in new context
             for (Type t : inferencevars) {
                 that.freeTypeListeners.put(new FreeTypeListener() {
                     public void typesInferred(InferenceContext inferenceContext) {
                         InferenceContext.this.notifyChange();
                     }
                 }, List.of(t));
             }
         }
         private void solve(GraphStrategy ss, Warner warn) {
             solve(ss, new HashMap<Type, Set<Type>>(), warn);
         }
         /**
          * Solve with given graph strategy.
          */
         private void solve(GraphStrategy ss, Map<Type, Set<Type>> stuckDeps, Warner warn) {
             GraphSolver s = new GraphSolver(this, stuckDeps, warn);
             s.solve(ss);
         }
         /**
          * Solve all variables in this context.
          */
         public void solve(Warner warn) {
             solve(new LeafSolver() {
                 public boolean done() {
                     return restvars().isEmpty();
                 }
             }, warn);
         }
         /**
          * Solve all variables in the given list.
          */
         public void solve(final List<Type> vars, Warner warn) {
             solve(new BestLeafSolver(vars) {
                 public boolean done() {
                     return !free(asInstTypes(vars));
                 }
             }, warn);
         }
         /**
          * Solve at least one variable in given list.
          */
         public void solveAny(List<Type> varsToSolve, Map<Type, Set<Type>> optDeps, Warner warn) {
             solve(new BestLeafSolver(varsToSolve.intersect(restvars())) {
                 public boolean done() {
                     return instvars().intersect(varsToSolve).nonEmpty();
                 }
             }, optDeps, warn);
         }
         /**
          * Apply a set of inference steps
          */
         private boolean solveBasic(EnumSet<InferenceStep> steps) {
             return solveBasic(inferencevars, steps);
         }
         private boolean solveBasic(List<Type> varsToSolve, EnumSet<InferenceStep> steps) {
             boolean changed = false;
             for (Type t : varsToSolve.intersect(restvars())) {
                 UndetVar uv = (UndetVar)asUndetVar(t);
                 for (InferenceStep step : steps) {
                     if (step.accepts(uv, this)) {
                         uv.inst = step.solve(uv, this);
                         changed = true;
                         break;
                     }
                 }
             }
             return changed;
         }
         /**
          * Instantiate inference variables in legacy mode (JLS 15.12.2.7, 15.12.2.8).
          * During overload resolution, instantiation is done by doing a partial
          * inference process using eq/lower bound instantiation. During check,
          * we also instantiate any remaining vars by repeatedly using eq/upper
          * instantiation, until all variables are solved.
          */
         public void solveLegacy(boolean partial, Warner warn, EnumSet<InferenceStep> steps) {
             while (true) {
                 boolean stuck = !solveBasic(steps);
                 if (restvars().isEmpty() || partial) {
                     //all variables have been instantiated - exit
                     break;
                 } else if (stuck) {
                     //some variables could not be instantiated because of cycles in
                     //upper bounds - provide a (possibly recursive) default instantiation
                     instantiateAsUninferredVars(restvars(), this);
                     break;
                 } else {
                     //some variables have been instantiated - replace newly instantiated
                     //variables in remaining upper bounds and continue
                     for (Type t : undetvars) {
                         UndetVar uv = (UndetVar)t;
                         uv.substBounds(inferenceVars(), instTypes(), types);
                     }
                 }
             }
             checkWithinBounds(this, warn);
         }
         private Infer infer() {
             //back-door to infer
             return Infer.this;
         }
         @Override
         public String toString() {
             return "Inference vars: " + inferencevars + '\n' +
                    "Undet vars: " + undetvars;
         }
         /* Method Types.capture() generates a new type every time it's applied
          * to a wildcard parameterized type. This is intended functionality but
          * there are some cases when what you need is not to generate a new
          * captured type but to check that a previously generated captured type
          * is correct. There are cases when caching a captured type for later
          * reuse is sound. In general two captures from the same AST are equal.
          * This is why the tree is used as the key of the map below. This map
          * stores a Type per AST.
          */
         Map<JCTree, Type> captureTypeCache = new HashMap<>();
         Type cachedCapture(JCTree tree, Type t, boolean readOnly) {
             Type captured = captureTypeCache.get(tree);
             if (captured != null) {
                 return captured;
             }
             Type result = types.capture(t);
             if (result != t && !readOnly) { // then t is a wildcard parameterized type
                 captureTypeCache.put(tree, result);
             }
             return result;
         }
     }
     final InferenceContext emptyContext = new InferenceContext(List.<Type>nil());
     // </editor-fold>
 }

Mercurial > jdk8-mips64-public > langtools / annotate

src/share/classes/com/sun/tools/javac/comp/Infer.java@c6d5efccedc3 (annotated)

src/share/classes/com/sun/tools/javac/comp/Infer.java