Fri, 15 Feb 2013 16:29:58 +0000
8007462: Fix provisional applicability for method references
Summary: Add speculative arity-based check to rule out potential candidates when stuck reference is passed to method
Reviewed-by: jjg
1 /*
2 * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
26 package com.sun.tools.javac.comp;
28 import com.sun.tools.javac.code.*;
29 import com.sun.tools.javac.tree.*;
30 import com.sun.tools.javac.util.*;
31 import com.sun.tools.javac.code.Symbol.*;
32 import com.sun.tools.javac.code.Type.*;
33 import com.sun.tools.javac.comp.Attr.ResultInfo;
34 import com.sun.tools.javac.comp.Infer.InferenceContext;
35 import com.sun.tools.javac.comp.Resolve.MethodResolutionPhase;
36 import com.sun.tools.javac.tree.JCTree.*;
38 import javax.tools.JavaFileObject;
40 import java.util.ArrayList;
41 import java.util.EnumSet;
42 import java.util.LinkedHashSet;
43 import java.util.Map;
44 import java.util.Queue;
45 import java.util.Set;
46 import java.util.WeakHashMap;
48 import static com.sun.tools.javac.code.TypeTag.*;
49 import static com.sun.tools.javac.tree.JCTree.Tag.*;
51 /**
52 * This is an helper class that is used to perform deferred type-analysis.
53 * Each time a poly expression occurs in argument position, javac attributes it
54 * with a temporary 'deferred type' that is checked (possibly multiple times)
55 * against an expected formal type.
56 *
57 * <p><b>This is NOT part of any supported API.
58 * If you write code that depends on this, you do so at your own risk.
59 * This code and its internal interfaces are subject to change or
60 * deletion without notice.</b>
61 */
62 public class DeferredAttr extends JCTree.Visitor {
63 protected static final Context.Key<DeferredAttr> deferredAttrKey =
64 new Context.Key<DeferredAttr>();
66 final Attr attr;
67 final Check chk;
68 final JCDiagnostic.Factory diags;
69 final Enter enter;
70 final Infer infer;
71 final Resolve rs;
72 final Log log;
73 final Symtab syms;
74 final TreeMaker make;
75 final Types types;
77 public static DeferredAttr instance(Context context) {
78 DeferredAttr instance = context.get(deferredAttrKey);
79 if (instance == null)
80 instance = new DeferredAttr(context);
81 return instance;
82 }
84 protected DeferredAttr(Context context) {
85 context.put(deferredAttrKey, this);
86 attr = Attr.instance(context);
87 chk = Check.instance(context);
88 diags = JCDiagnostic.Factory.instance(context);
89 enter = Enter.instance(context);
90 infer = Infer.instance(context);
91 rs = Resolve.instance(context);
92 log = Log.instance(context);
93 syms = Symtab.instance(context);
94 make = TreeMaker.instance(context);
95 types = Types.instance(context);
96 Names names = Names.instance(context);
97 stuckTree = make.Ident(names.empty).setType(Type.noType);
98 }
100 /** shared tree for stuck expressions */
101 final JCTree stuckTree;
103 /**
104 * This type represents a deferred type. A deferred type starts off with
105 * no information on the underlying expression type. Such info needs to be
106 * discovered through type-checking the deferred type against a target-type.
107 * Every deferred type keeps a pointer to the AST node from which it originated.
108 */
109 public class DeferredType extends Type {
111 public JCExpression tree;
112 Env<AttrContext> env;
113 AttrMode mode;
114 SpeculativeCache speculativeCache;
116 DeferredType(JCExpression tree, Env<AttrContext> env) {
117 super(DEFERRED, null);
118 this.tree = tree;
119 this.env = env.dup(tree, env.info.dup());
120 this.speculativeCache = new SpeculativeCache();
121 }
123 /**
124 * A speculative cache is used to keep track of all overload resolution rounds
125 * that triggered speculative attribution on a given deferred type. Each entry
126 * stores a pointer to the speculative tree and the resolution phase in which the entry
127 * has been added.
128 */
129 class SpeculativeCache {
131 private Map<Symbol, List<Entry>> cache =
132 new WeakHashMap<Symbol, List<Entry>>();
134 class Entry {
135 JCTree speculativeTree;
136 Resolve.MethodResolutionPhase phase;
138 public Entry(JCTree speculativeTree, MethodResolutionPhase phase) {
139 this.speculativeTree = speculativeTree;
140 this.phase = phase;
141 }
143 boolean matches(Resolve.MethodResolutionPhase phase) {
144 return this.phase == phase;
145 }
146 }
148 /**
149 * Retrieve a speculative cache entry corresponding to given symbol
150 * and resolution phase
151 */
152 Entry get(Symbol msym, MethodResolutionPhase phase) {
153 List<Entry> entries = cache.get(msym);
154 if (entries == null) return null;
155 for (Entry e : entries) {
156 if (e.matches(phase)) return e;
157 }
158 return null;
159 }
161 /**
162 * Stores a speculative cache entry corresponding to given symbol
163 * and resolution phase
164 */
165 void put(Symbol msym, JCTree speculativeTree, MethodResolutionPhase phase) {
166 List<Entry> entries = cache.get(msym);
167 if (entries == null) {
168 entries = List.nil();
169 }
170 cache.put(msym, entries.prepend(new Entry(speculativeTree, phase)));
171 }
172 }
174 /**
175 * Get the type that has been computed during a speculative attribution round
176 */
177 Type speculativeType(Symbol msym, MethodResolutionPhase phase) {
178 SpeculativeCache.Entry e = speculativeCache.get(msym, phase);
179 return e != null ? e.speculativeTree.type : Type.noType;
180 }
182 /**
183 * Check a deferred type against a potential target-type. Depending on
184 * the current attribution mode, a normal vs. speculative attribution
185 * round is performed on the underlying AST node. There can be only one
186 * speculative round for a given target method symbol; moreover, a normal
187 * attribution round must follow one or more speculative rounds.
188 */
189 Type check(ResultInfo resultInfo) {
190 return check(resultInfo, stuckVars(tree, env, resultInfo), basicCompleter);
191 }
193 Type check(ResultInfo resultInfo, List<Type> stuckVars, DeferredTypeCompleter deferredTypeCompleter) {
194 DeferredAttrContext deferredAttrContext =
195 resultInfo.checkContext.deferredAttrContext();
196 Assert.check(deferredAttrContext != emptyDeferredAttrContext);
197 if (stuckVars.nonEmpty()) {
198 deferredAttrContext.addDeferredAttrNode(this, resultInfo, stuckVars);
199 return Type.noType;
200 } else {
201 try {
202 return deferredTypeCompleter.complete(this, resultInfo, deferredAttrContext);
203 } finally {
204 mode = deferredAttrContext.mode;
205 }
206 }
207 }
208 }
210 /**
211 * A completer for deferred types. Defines an entry point for type-checking
212 * a deferred type.
213 */
214 interface DeferredTypeCompleter {
215 /**
216 * Entry point for type-checking a deferred type. Depending on the
217 * circumstances, type-checking could amount to full attribution
218 * or partial structural check (aka potential applicability).
219 */
220 Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext);
221 }
223 /**
224 * A basic completer for deferred types. This completer type-checks a deferred type
225 * using attribution; depending on the attribution mode, this could be either standard
226 * or speculative attribution.
227 */
228 DeferredTypeCompleter basicCompleter = new DeferredTypeCompleter() {
229 public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
230 switch (deferredAttrContext.mode) {
231 case SPECULATIVE:
232 Assert.check(dt.mode == null ||
233 (dt.mode == AttrMode.SPECULATIVE &&
234 dt.speculativeType(deferredAttrContext.msym, deferredAttrContext.phase).hasTag(NONE)));
235 JCTree speculativeTree = attribSpeculative(dt.tree, dt.env, resultInfo);
236 dt.speculativeCache.put(deferredAttrContext.msym, speculativeTree, deferredAttrContext.phase);
237 return speculativeTree.type;
238 case CHECK:
239 Assert.check(dt.mode != null);
240 return attr.attribTree(dt.tree, dt.env, resultInfo);
241 }
242 Assert.error();
243 return null;
244 }
245 };
247 DeferredTypeCompleter dummyCompleter = new DeferredTypeCompleter() {
248 public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
249 Assert.check(deferredAttrContext.mode == AttrMode.CHECK);
250 return dt.tree.type = Type.noType;
251 }
252 };
254 /**
255 * The 'mode' in which the deferred type is to be type-checked
256 */
257 public enum AttrMode {
258 /**
259 * A speculative type-checking round is used during overload resolution
260 * mainly to generate constraints on inference variables. Side-effects
261 * arising from type-checking the expression associated with the deferred
262 * type are reversed after the speculative round finishes. This means the
263 * expression tree will be left in a blank state.
264 */
265 SPECULATIVE,
266 /**
267 * This is the plain type-checking mode. Produces side-effects on the underlying AST node
268 */
269 CHECK;
270 }
272 /**
273 * Routine that performs speculative type-checking; the input AST node is
274 * cloned (to avoid side-effects cause by Attr) and compiler state is
275 * restored after type-checking. All diagnostics (but critical ones) are
276 * disabled during speculative type-checking.
277 */
278 JCTree attribSpeculative(JCTree tree, Env<AttrContext> env, ResultInfo resultInfo) {
279 JCTree newTree = new TreeCopier<Object>(make).copy(tree);
280 Env<AttrContext> speculativeEnv = env.dup(newTree, env.info.dup(env.info.scope.dupUnshared()));
281 speculativeEnv.info.scope.owner = env.info.scope.owner;
282 final JavaFileObject currentSource = log.currentSourceFile();
283 Log.DeferredDiagnosticHandler deferredDiagnosticHandler =
284 new Log.DeferredDiagnosticHandler(log, new Filter<JCDiagnostic>() {
285 public boolean accepts(JCDiagnostic t) {
286 return t.getDiagnosticSource().getFile().equals(currentSource);
287 }
288 });
289 try {
290 attr.attribTree(newTree, speculativeEnv, resultInfo);
291 unenterScanner.scan(newTree);
292 return newTree;
293 } catch (Abort ex) {
294 //if some very bad condition occurred during deferred attribution
295 //we should dump all errors before killing javac
296 deferredDiagnosticHandler.reportDeferredDiagnostics();
297 throw ex;
298 } finally {
299 unenterScanner.scan(newTree);
300 log.popDiagnosticHandler(deferredDiagnosticHandler);
301 }
302 }
303 //where
304 protected TreeScanner unenterScanner = new TreeScanner() {
305 @Override
306 public void visitClassDef(JCClassDecl tree) {
307 ClassSymbol csym = tree.sym;
308 //if something went wrong during method applicability check
309 //it is possible that nested expressions inside argument expression
310 //are left unchecked - in such cases there's nothing to clean up.
311 if (csym == null) return;
312 enter.typeEnvs.remove(csym);
313 chk.compiled.remove(csym.flatname);
314 syms.classes.remove(csym.flatname);
315 super.visitClassDef(tree);
316 }
317 };
319 /**
320 * A deferred context is created on each method check. A deferred context is
321 * used to keep track of information associated with the method check, such as
322 * the symbol of the method being checked, the overload resolution phase,
323 * the kind of attribution mode to be applied to deferred types and so forth.
324 * As deferred types are processed (by the method check routine) stuck AST nodes
325 * are added (as new deferred attribution nodes) to this context. The complete()
326 * routine makes sure that all pending nodes are properly processed, by
327 * progressively instantiating all inference variables on which one or more
328 * deferred attribution node is stuck.
329 */
330 class DeferredAttrContext {
332 /** attribution mode */
333 final AttrMode mode;
335 /** symbol of the method being checked */
336 final Symbol msym;
338 /** method resolution step */
339 final Resolve.MethodResolutionPhase phase;
341 /** inference context */
342 final InferenceContext inferenceContext;
344 /** parent deferred context */
345 final DeferredAttrContext parent;
347 /** Warner object to report warnings */
348 final Warner warn;
350 /** list of deferred attribution nodes to be processed */
351 ArrayList<DeferredAttrNode> deferredAttrNodes = new ArrayList<DeferredAttrNode>();
353 DeferredAttrContext(AttrMode mode, Symbol msym, MethodResolutionPhase phase,
354 InferenceContext inferenceContext, DeferredAttrContext parent, Warner warn) {
355 this.mode = mode;
356 this.msym = msym;
357 this.phase = phase;
358 this.parent = parent;
359 this.warn = warn;
360 this.inferenceContext = inferenceContext;
361 }
363 /**
364 * Adds a node to the list of deferred attribution nodes - used by Resolve.rawCheckArgumentsApplicable
365 * Nodes added this way act as 'roots' for the out-of-order method checking process.
366 */
367 void addDeferredAttrNode(final DeferredType dt, ResultInfo resultInfo, List<Type> stuckVars) {
368 deferredAttrNodes.add(new DeferredAttrNode(dt, resultInfo, stuckVars));
369 }
371 /**
372 * Incrementally process all nodes, by skipping 'stuck' nodes and attributing
373 * 'unstuck' ones. If at any point no progress can be made (no 'unstuck' nodes)
374 * some inference variable might get eagerly instantiated so that all nodes
375 * can be type-checked.
376 */
377 void complete() {
378 while (!deferredAttrNodes.isEmpty()) {
379 Set<Type> stuckVars = new LinkedHashSet<Type>();
380 boolean progress = false;
381 //scan a defensive copy of the node list - this is because a deferred
382 //attribution round can add new nodes to the list
383 for (DeferredAttrNode deferredAttrNode : List.from(deferredAttrNodes)) {
384 if (!deferredAttrNode.process(this)) {
385 stuckVars.addAll(deferredAttrNode.stuckVars);
386 } else {
387 deferredAttrNodes.remove(deferredAttrNode);
388 progress = true;
389 }
390 }
391 if (!progress) {
392 //remove all variables that have already been instantiated
393 //from the list of stuck variables
394 inferenceContext.solveAny(List.from(stuckVars), warn);
395 inferenceContext.notifyChange();
396 }
397 }
398 }
399 }
401 /**
402 * Class representing a deferred attribution node. It keeps track of
403 * a deferred type, along with the expected target type information.
404 */
405 class DeferredAttrNode implements Infer.FreeTypeListener {
407 /** underlying deferred type */
408 DeferredType dt;
410 /** underlying target type information */
411 ResultInfo resultInfo;
413 /** list of uninferred inference variables causing this node to be stuck */
414 List<Type> stuckVars;
416 DeferredAttrNode(DeferredType dt, ResultInfo resultInfo, List<Type> stuckVars) {
417 this.dt = dt;
418 this.resultInfo = resultInfo;
419 this.stuckVars = stuckVars;
420 if (!stuckVars.isEmpty()) {
421 resultInfo.checkContext.inferenceContext().addFreeTypeListener(stuckVars, this);
422 }
423 }
425 @Override
426 public void typesInferred(InferenceContext inferenceContext) {
427 stuckVars = List.nil();
428 resultInfo = resultInfo.dup(inferenceContext.asInstType(resultInfo.pt));
429 }
431 /**
432 * Process a deferred attribution node.
433 * Invariant: a stuck node cannot be processed.
434 */
435 @SuppressWarnings("fallthrough")
436 boolean process(DeferredAttrContext deferredAttrContext) {
437 switch (deferredAttrContext.mode) {
438 case SPECULATIVE:
439 dt.check(resultInfo, List.<Type>nil(), new StructuralStuckChecker());
440 return true;
441 case CHECK:
442 if (stuckVars.nonEmpty()) {
443 //stuck expression - see if we can propagate
444 if (deferredAttrContext.parent != emptyDeferredAttrContext &&
445 Type.containsAny(deferredAttrContext.parent.inferenceContext.inferencevars, List.from(stuckVars))) {
446 deferredAttrContext.parent.deferredAttrNodes.add(this);
447 dt.check(resultInfo, List.<Type>nil(), dummyCompleter);
448 return true;
449 } else {
450 return false;
451 }
452 } else {
453 dt.check(resultInfo, stuckVars, basicCompleter);
454 return true;
455 }
456 default:
457 throw new AssertionError("Bad mode");
458 }
459 }
461 /**
462 * Structural checker for stuck expressions
463 */
464 class StructuralStuckChecker extends TreeScanner implements DeferredTypeCompleter {
466 ResultInfo resultInfo;
467 InferenceContext inferenceContext;
468 Env<AttrContext> env;
470 public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
471 this.resultInfo = resultInfo;
472 this.inferenceContext = deferredAttrContext.inferenceContext;
473 this.env = dt.env.dup(dt.tree, dt.env.info.dup());
474 dt.tree.accept(this);
475 dt.speculativeCache.put(deferredAttrContext.msym, stuckTree, deferredAttrContext.phase);
476 return Type.noType;
477 }
479 @Override
480 public void visitLambda(JCLambda tree) {
481 Check.CheckContext checkContext = resultInfo.checkContext;
482 Type pt = resultInfo.pt;
483 if (inferenceContext.inferencevars.contains(pt)) {
484 //ok
485 return;
486 } else {
487 //must be a functional descriptor
488 try {
489 Type desc = types.findDescriptorType(pt);
490 if (desc.getParameterTypes().length() != tree.params.length()) {
491 checkContext.report(tree, diags.fragment("incompatible.arg.types.in.lambda"));
492 }
493 } catch (Types.FunctionDescriptorLookupError ex) {
494 checkContext.report(null, ex.getDiagnostic());
495 }
496 }
497 }
499 @Override
500 public void visitNewClass(JCNewClass tree) {
501 //do nothing
502 }
504 @Override
505 public void visitApply(JCMethodInvocation tree) {
506 //do nothing
507 }
509 @Override
510 public void visitReference(JCMemberReference tree) {
511 Check.CheckContext checkContext = resultInfo.checkContext;
512 Type pt = resultInfo.pt;
513 if (inferenceContext.inferencevars.contains(pt)) {
514 //ok
515 return;
516 } else {
517 try {
518 types.findDescriptorType(pt);
519 } catch (Types.FunctionDescriptorLookupError ex) {
520 checkContext.report(null, ex.getDiagnostic());
521 }
522 JCExpression exprTree = (JCExpression)attribSpeculative(tree.getQualifierExpression(), env,
523 attr.memberReferenceQualifierResult(tree));
524 ListBuffer<Type> argtypes = ListBuffer.lb();
525 for (Type t : types.findDescriptorType(pt).getParameterTypes()) {
526 argtypes.append(syms.errType);
527 }
528 JCMemberReference mref2 = new TreeCopier<Void>(make).copy(tree);
529 mref2.expr = exprTree;
530 Pair<Symbol, ?> lookupRes =
531 rs.resolveMemberReference(tree, env, mref2, exprTree.type, tree.name, argtypes.toList(), null, true);
532 switch (lookupRes.fst.kind) {
533 //note: as argtypes are erroneous types, type-errors must
534 //have been caused by arity mismatch
535 case Kinds.ABSENT_MTH:
536 case Kinds.WRONG_MTH:
537 case Kinds.WRONG_MTHS:
538 case Kinds.STATICERR:
539 case Kinds.MISSING_ENCL:
540 checkContext.report(null, diags.fragment("incompatible.arg.types.in.mref"));
541 }
542 }
543 }
544 }
545 }
547 /** an empty deferred attribution context - all methods throw exceptions */
548 final DeferredAttrContext emptyDeferredAttrContext =
549 new DeferredAttrContext(AttrMode.CHECK, null, MethodResolutionPhase.BOX, null, null, null) {
550 @Override
551 void addDeferredAttrNode(DeferredType dt, ResultInfo ri, List<Type> stuckVars) {
552 Assert.error("Empty deferred context!");
553 }
554 @Override
555 void complete() {
556 Assert.error("Empty deferred context!");
557 }
558 };
560 /**
561 * Map a list of types possibly containing one or more deferred types
562 * into a list of ordinary types. Each deferred type D is mapped into a type T,
563 * where T is computed by retrieving the type that has already been
564 * computed for D during a previous deferred attribution round of the given kind.
565 */
566 class DeferredTypeMap extends Type.Mapping {
568 DeferredAttrContext deferredAttrContext;
570 protected DeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {
571 super(String.format("deferredTypeMap[%s]", mode));
572 this.deferredAttrContext = new DeferredAttrContext(mode, msym, phase,
573 infer.emptyContext, emptyDeferredAttrContext, types.noWarnings);
574 }
576 protected boolean validState(DeferredType dt) {
577 return dt.mode != null &&
578 deferredAttrContext.mode.ordinal() <= dt.mode.ordinal();
579 }
581 @Override
582 public Type apply(Type t) {
583 if (!t.hasTag(DEFERRED)) {
584 return t.map(this);
585 } else {
586 DeferredType dt = (DeferredType)t;
587 Assert.check(validState(dt));
588 return typeOf(dt);
589 }
590 }
592 protected Type typeOf(DeferredType dt) {
593 switch (deferredAttrContext.mode) {
594 case CHECK:
595 return dt.tree.type == null ? Type.noType : dt.tree.type;
596 case SPECULATIVE:
597 return dt.speculativeType(deferredAttrContext.msym, deferredAttrContext.phase);
598 }
599 Assert.error();
600 return null;
601 }
602 }
604 /**
605 * Specialized recovery deferred mapping.
606 * Each deferred type D is mapped into a type T, where T is computed either by
607 * (i) retrieving the type that has already been computed for D during a previous
608 * attribution round (as before), or (ii) by synthesizing a new type R for D
609 * (the latter step is useful in a recovery scenario).
610 */
611 public class RecoveryDeferredTypeMap extends DeferredTypeMap {
613 public RecoveryDeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {
614 super(mode, msym, phase != null ? phase : MethodResolutionPhase.BOX);
615 }
617 @Override
618 protected Type typeOf(DeferredType dt) {
619 Type owntype = super.typeOf(dt);
620 return owntype == Type.noType ?
621 recover(dt) : owntype;
622 }
624 @Override
625 protected boolean validState(DeferredType dt) {
626 return true;
627 }
629 /**
630 * Synthesize a type for a deferred type that hasn't been previously
631 * reduced to an ordinary type. Functional deferred types and conditionals
632 * are mapped to themselves, in order to have a richer diagnostic
633 * representation. Remaining deferred types are attributed using
634 * a default expected type (j.l.Object).
635 */
636 private Type recover(DeferredType dt) {
637 dt.check(attr.new RecoveryInfo(deferredAttrContext));
638 return super.apply(dt);
639 }
640 }
642 /**
643 * Retrieves the list of inference variables that need to be inferred before
644 * an AST node can be type-checked
645 */
646 @SuppressWarnings("fallthrough")
647 List<Type> stuckVars(JCTree tree, Env<AttrContext> env, ResultInfo resultInfo) {
648 if (resultInfo.pt.hasTag(NONE) || resultInfo.pt.isErroneous()) {
649 return List.nil();
650 } else {
651 return stuckVarsInternal(tree, resultInfo.pt, resultInfo.checkContext.inferenceContext());
652 }
653 }
654 //where
655 private List<Type> stuckVarsInternal(JCTree tree, Type pt, Infer.InferenceContext inferenceContext) {
656 StuckChecker sc = new StuckChecker(pt, inferenceContext);
657 sc.scan(tree);
658 return List.from(sc.stuckVars);
659 }
661 /**
662 * A special tree scanner that would only visit portions of a given tree.
663 * The set of nodes visited by the scanner can be customized at construction-time.
664 */
665 abstract static class FilterScanner extends TreeScanner {
667 final Filter<JCTree> treeFilter;
669 FilterScanner(final Set<JCTree.Tag> validTags) {
670 this.treeFilter = new Filter<JCTree>() {
671 public boolean accepts(JCTree t) {
672 return validTags.contains(t.getTag());
673 }
674 };
675 }
677 @Override
678 public void scan(JCTree tree) {
679 if (tree != null) {
680 if (treeFilter.accepts(tree)) {
681 super.scan(tree);
682 } else {
683 skip(tree);
684 }
685 }
686 }
688 /**
689 * handler that is executed when a node has been discarded
690 */
691 abstract void skip(JCTree tree);
692 }
694 /**
695 * A tree scanner suitable for visiting the target-type dependent nodes of
696 * a given argument expression.
697 */
698 static class PolyScanner extends FilterScanner {
700 PolyScanner() {
701 super(EnumSet.of(CONDEXPR, PARENS, LAMBDA, REFERENCE));
702 }
704 @Override
705 void skip(JCTree tree) {
706 //do nothing
707 }
708 }
710 /**
711 * A tree scanner suitable for visiting the target-type dependent nodes nested
712 * within a lambda expression body.
713 */
714 static class LambdaReturnScanner extends FilterScanner {
716 LambdaReturnScanner() {
717 super(EnumSet.of(BLOCK, CASE, CATCH, DOLOOP, FOREACHLOOP,
718 FORLOOP, RETURN, SYNCHRONIZED, SWITCH, TRY, WHILELOOP));
719 }
721 @Override
722 void skip(JCTree tree) {
723 //do nothing
724 }
725 }
727 /**
728 * This visitor is used to check that structural expressions conform
729 * to their target - this step is required as inference could end up
730 * inferring types that make some of the nested expressions incompatible
731 * with their corresponding instantiated target
732 */
733 class StuckChecker extends PolyScanner {
735 Type pt;
736 Infer.InferenceContext inferenceContext;
737 Set<Type> stuckVars = new LinkedHashSet<Type>();
739 StuckChecker(Type pt, Infer.InferenceContext inferenceContext) {
740 this.pt = pt;
741 this.inferenceContext = inferenceContext;
742 }
744 @Override
745 public void visitLambda(JCLambda tree) {
746 if (inferenceContext.inferenceVars().contains(pt)) {
747 stuckVars.add(pt);
748 }
749 if (!types.isFunctionalInterface(pt)) {
750 return;
751 }
752 Type descType = types.findDescriptorType(pt);
753 List<Type> freeArgVars = inferenceContext.freeVarsIn(descType.getParameterTypes());
754 if (tree.paramKind == JCLambda.ParameterKind.IMPLICIT &&
755 freeArgVars.nonEmpty()) {
756 stuckVars.addAll(freeArgVars);
757 }
758 scanLambdaBody(tree, descType.getReturnType());
759 }
761 @Override
762 public void visitReference(JCMemberReference tree) {
763 scan(tree.expr);
764 if (inferenceContext.inferenceVars().contains(pt)) {
765 stuckVars.add(pt);
766 return;
767 }
768 if (!types.isFunctionalInterface(pt)) {
769 return;
770 }
772 Type descType = types.findDescriptorType(pt);
773 List<Type> freeArgVars = inferenceContext.freeVarsIn(descType.getParameterTypes());
774 stuckVars.addAll(freeArgVars);
775 }
777 void scanLambdaBody(JCLambda lambda, final Type pt) {
778 if (lambda.getBodyKind() == JCTree.JCLambda.BodyKind.EXPRESSION) {
779 stuckVars.addAll(stuckVarsInternal(lambda.body, pt, inferenceContext));
780 } else {
781 LambdaReturnScanner lambdaScanner = new LambdaReturnScanner() {
782 @Override
783 public void visitReturn(JCReturn tree) {
784 if (tree.expr != null) {
785 stuckVars.addAll(stuckVarsInternal(tree.expr, pt, inferenceContext));
786 }
787 }
788 };
789 lambdaScanner.scan(lambda.body);
790 }
791 }
792 }
793 }