Infer.java revision 4011:28a6e8d3ccc7
1/* 2 * Copyright (c) 1999, 2017, 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 */ 25 26package com.sun.tools.javac.comp; 27 28import com.sun.tools.javac.code.Type.UndetVar.UndetVarListener; 29import com.sun.tools.javac.tree.JCTree; 30import com.sun.tools.javac.tree.JCTree.JCTypeCast; 31import com.sun.tools.javac.tree.TreeInfo; 32import com.sun.tools.javac.util.*; 33import com.sun.tools.javac.util.GraphUtils.DottableNode; 34import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition; 35import com.sun.tools.javac.util.List; 36import com.sun.tools.javac.code.*; 37import com.sun.tools.javac.code.Type.*; 38import com.sun.tools.javac.code.Type.UndetVar.InferenceBound; 39import com.sun.tools.javac.code.Symbol.*; 40import com.sun.tools.javac.comp.DeferredAttr.AttrMode; 41import com.sun.tools.javac.comp.DeferredAttr.DeferredAttrContext; 42import com.sun.tools.javac.comp.Infer.GraphSolver.InferenceGraph; 43import com.sun.tools.javac.comp.Infer.GraphSolver.InferenceGraph.Node; 44import com.sun.tools.javac.comp.Resolve.InapplicableMethodException; 45import com.sun.tools.javac.comp.Resolve.VerboseResolutionMode; 46 47import java.io.IOException; 48import java.io.Writer; 49import java.nio.file.Files; 50import java.nio.file.Path; 51import java.nio.file.Paths; 52import java.util.ArrayList; 53import java.util.Collection; 54import java.util.Collections; 55import java.util.EnumSet; 56import java.util.HashMap; 57import java.util.HashSet; 58import java.util.Map; 59import java.util.Optional; 60import java.util.Properties; 61import java.util.Set; 62import java.util.function.BiFunction; 63import java.util.function.BiPredicate; 64import java.util.stream.Collectors; 65 66import com.sun.tools.javac.main.Option; 67 68import static com.sun.tools.javac.code.TypeTag.*; 69 70/** Helper class for type parameter inference, used by the attribution phase. 71 * 72 * <p><b>This is NOT part of any supported API. 73 * If you write code that depends on this, you do so at your own risk. 74 * This code and its internal interfaces are subject to change or 75 * deletion without notice.</b> 76 */ 77public class Infer { 78 protected static final Context.Key<Infer> inferKey = new Context.Key<>(); 79 80 Resolve rs; 81 Check chk; 82 Symtab syms; 83 Types types; 84 JCDiagnostic.Factory diags; 85 Log log; 86 87 /** should the graph solver be used? */ 88 boolean allowGraphInference; 89 90 /** 91 * folder in which the inference dependency graphs should be written. 92 */ 93 private final String dependenciesFolder; 94 95 /** 96 * List of graphs awaiting to be dumped to a file. 97 */ 98 private List<String> pendingGraphs; 99 100 public static Infer instance(Context context) { 101 Infer instance = context.get(inferKey); 102 if (instance == null) 103 instance = new Infer(context); 104 return instance; 105 } 106 107 protected Infer(Context context) { 108 context.put(inferKey, this); 109 110 rs = Resolve.instance(context); 111 chk = Check.instance(context); 112 syms = Symtab.instance(context); 113 types = Types.instance(context); 114 diags = JCDiagnostic.Factory.instance(context); 115 log = Log.instance(context); 116 inferenceException = new InferenceException(diags); 117 Options options = Options.instance(context); 118 allowGraphInference = Source.instance(context).allowGraphInference() 119 && options.isUnset("useLegacyInference"); 120 dependenciesFolder = options.get("debug.dumpInferenceGraphsTo"); 121 pendingGraphs = List.nil(); 122 123 emptyContext = new InferenceContext(this, List.nil()); 124 } 125 126 /** A value for prototypes that admit any type, including polymorphic ones. */ 127 public static final Type anyPoly = new JCNoType(); 128 129 /** 130 * This exception class is design to store a list of diagnostics corresponding 131 * to inference errors that can arise during a method applicability check. 132 */ 133 public static class InferenceException extends InapplicableMethodException { 134 private static final long serialVersionUID = 0; 135 136 List<JCDiagnostic> messages = List.nil(); 137 138 InferenceException(JCDiagnostic.Factory diags) { 139 super(diags); 140 } 141 142 @Override 143 InapplicableMethodException setMessage() { 144 //no message to set 145 return this; 146 } 147 148 @Override 149 InapplicableMethodException setMessage(JCDiagnostic diag) { 150 messages = messages.append(diag); 151 return this; 152 } 153 154 @Override 155 public JCDiagnostic getDiagnostic() { 156 return messages.head; 157 } 158 159 void clear() { 160 messages = List.nil(); 161 } 162 } 163 164 protected final InferenceException inferenceException; 165 166 // <editor-fold defaultstate="collapsed" desc="Inference routines"> 167 /** 168 * Main inference entry point - instantiate a generic method type 169 * using given argument types and (possibly) an expected target-type. 170 */ 171 Type instantiateMethod( Env<AttrContext> env, 172 List<Type> tvars, 173 MethodType mt, 174 Attr.ResultInfo resultInfo, 175 MethodSymbol msym, 176 List<Type> argtypes, 177 boolean allowBoxing, 178 boolean useVarargs, 179 Resolve.MethodResolutionContext resolveContext, 180 Warner warn) throws InferenceException { 181 //-System.err.println("instantiateMethod(" + tvars + ", " + mt + ", " + argtypes + ")"); //DEBUG 182 final InferenceContext inferenceContext = new InferenceContext(this, tvars); //B0 183 inferenceException.clear(); 184 try { 185 DeferredAttr.DeferredAttrContext deferredAttrContext = 186 resolveContext.deferredAttrContext(msym, inferenceContext, resultInfo, warn); 187 188 resolveContext.methodCheck.argumentsAcceptable(env, deferredAttrContext, //B2 189 argtypes, mt.getParameterTypes(), warn); 190 191 if (allowGraphInference && resultInfo != null && resultInfo.pt == anyPoly) { 192 doIncorporation(inferenceContext, warn); 193 //we are inside method attribution - just return a partially inferred type 194 return new PartiallyInferredMethodType(mt, inferenceContext, env, warn); 195 } else if (allowGraphInference && 196 resultInfo != null && 197 !warn.hasNonSilentLint(Lint.LintCategory.UNCHECKED)) { 198 //inject return constraints earlier 199 doIncorporation(inferenceContext, warn); //propagation 200 201 boolean shouldPropagate = shouldPropagate(mt.getReturnType(), resultInfo, inferenceContext); 202 203 InferenceContext minContext = shouldPropagate ? 204 inferenceContext.min(roots(mt, deferredAttrContext), true, warn) : 205 inferenceContext; 206 207 Type newRestype = generateReturnConstraints(env.tree, resultInfo, //B3 208 mt, minContext); 209 mt = (MethodType)types.createMethodTypeWithReturn(mt, newRestype); 210 211 //propagate outwards if needed 212 if (shouldPropagate) { 213 //propagate inference context outwards and exit 214 minContext.dupTo(resultInfo.checkContext.inferenceContext()); 215 deferredAttrContext.complete(); 216 return mt; 217 } 218 } 219 220 deferredAttrContext.complete(); 221 222 // minimize as yet undetermined type variables 223 if (allowGraphInference) { 224 inferenceContext.solve(warn); 225 } else { 226 inferenceContext.solveLegacy(true, warn, LegacyInferenceSteps.EQ_LOWER.steps); //minimizeInst 227 } 228 229 mt = (MethodType)inferenceContext.asInstType(mt); 230 231 if (!allowGraphInference && 232 inferenceContext.restvars().nonEmpty() && 233 resultInfo != null && 234 !warn.hasNonSilentLint(Lint.LintCategory.UNCHECKED)) { 235 generateReturnConstraints(env.tree, resultInfo, mt, inferenceContext); 236 inferenceContext.solveLegacy(false, warn, LegacyInferenceSteps.EQ_UPPER.steps); //maximizeInst 237 mt = (MethodType)inferenceContext.asInstType(mt); 238 } 239 240 if (resultInfo != null && rs.verboseResolutionMode.contains(VerboseResolutionMode.DEFERRED_INST)) { 241 log.note(env.tree.pos, "deferred.method.inst", msym, mt, resultInfo.pt); 242 } 243 244 // return instantiated version of method type 245 return mt; 246 } finally { 247 if (resultInfo != null || !allowGraphInference) { 248 inferenceContext.notifyChange(); 249 } else { 250 inferenceContext.notifyChange(inferenceContext.boundedVars()); 251 } 252 if (resultInfo == null) { 253 /* if the is no result info then we can clear the capture types 254 * cache without affecting any result info check 255 */ 256 inferenceContext.captureTypeCache.clear(); 257 } 258 dumpGraphsIfNeeded(env.tree, msym, resolveContext); 259 } 260 } 261 //where 262 private boolean shouldPropagate(Type restype, Attr.ResultInfo target, InferenceContext inferenceContext) { 263 return target.checkContext.inferenceContext() != emptyContext && //enclosing context is a generic method 264 inferenceContext.free(restype) && //return type contains inference vars 265 (!inferenceContext.inferencevars.contains(restype) || //no eager instantiation is required (as per 18.5.2) 266 !needsEagerInstantiation((UndetVar)inferenceContext.asUndetVar(restype), target.pt, inferenceContext)); 267 } 268 269 private List<Type> roots(MethodType mt, DeferredAttrContext deferredAttrContext) { 270 ListBuffer<Type> roots = new ListBuffer<>(); 271 roots.add(mt.getReturnType()); 272 if (deferredAttrContext != null && deferredAttrContext.mode == AttrMode.CHECK) { 273 roots.addAll(mt.getThrownTypes()); 274 for (DeferredAttr.DeferredAttrNode n : deferredAttrContext.deferredAttrNodes) { 275 roots.addAll(n.deferredStuckPolicy.stuckVars()); 276 roots.addAll(n.deferredStuckPolicy.depVars()); 277 } 278 } 279 return roots.toList(); 280 } 281 282 /** 283 * A partially infered method/constructor type; such a type can be checked multiple times 284 * against different targets. 285 */ 286 public class PartiallyInferredMethodType extends MethodType { 287 public PartiallyInferredMethodType(MethodType mtype, InferenceContext inferenceContext, Env<AttrContext> env, Warner warn) { 288 super(mtype.getParameterTypes(), mtype.getReturnType(), mtype.getThrownTypes(), mtype.tsym); 289 this.inferenceContext = inferenceContext; 290 this.env = env; 291 this.warn = warn; 292 } 293 294 /** The inference context. */ 295 final InferenceContext inferenceContext; 296 297 /** The attribution environment. */ 298 Env<AttrContext> env; 299 300 /** The warner. */ 301 final Warner warn; 302 303 @Override 304 public boolean isPartial() { 305 return true; 306 } 307 308 /** 309 * Checks this type against a target; this means generating return type constraints, solve 310 * and then roll back the results (to avoid poolluting the context). 311 */ 312 Type check(Attr.ResultInfo resultInfo) { 313 Warner noWarnings = new Warner(null); 314 inferenceException.clear(); 315 List<Type> saved_undet = null; 316 try { 317 /** we need to save the inference context before generating target type constraints. 318 * This constraints may pollute the inference context and make it useless in case we 319 * need to use it several times: with several targets. 320 */ 321 saved_undet = inferenceContext.save(); 322 boolean unchecked = warn.hasNonSilentLint(Lint.LintCategory.UNCHECKED); 323 if (allowGraphInference && !unchecked) { 324 boolean shouldPropagate = shouldPropagate(getReturnType(), resultInfo, inferenceContext); 325 326 InferenceContext minContext = shouldPropagate ? 327 inferenceContext.min(roots(asMethodType(), null), false, warn) : 328 inferenceContext; 329 330 MethodType other = (MethodType)minContext.update(asMethodType()); 331 Type newRestype = generateReturnConstraints(env.tree, resultInfo, //B3 332 other, minContext); 333 334 if (shouldPropagate) { 335 //propagate inference context outwards and exit 336 minContext.dupTo(resultInfo.checkContext.inferenceContext(), 337 resultInfo.checkContext.deferredAttrContext().insideOverloadPhase()); 338 return newRestype; 339 } 340 } 341 inferenceContext.solve(noWarnings); 342 Type ret = inferenceContext.asInstType(this).getReturnType(); 343 //inline logic from Attr.checkMethod - if unchecked conversion was required, erase 344 //return type _after_ resolution 345 return unchecked ? types.erasure(ret) : ret; 346 } catch (InferenceException ex) { 347 resultInfo.checkContext.report(null, ex.getDiagnostic()); 348 Assert.error(); //cannot get here (the above should throw) 349 return null; 350 } finally { 351 if (saved_undet != null) { 352 inferenceContext.rollback(saved_undet); 353 } 354 } 355 } 356 } 357 358 private void dumpGraphsIfNeeded(DiagnosticPosition pos, Symbol msym, Resolve.MethodResolutionContext rsContext) { 359 int round = 0; 360 try { 361 for (String graph : pendingGraphs.reverse()) { 362 Assert.checkNonNull(dependenciesFolder); 363 Name name = msym.name == msym.name.table.names.init ? 364 msym.owner.name : msym.name; 365 String filename = String.format("%s@%s[mode=%s,step=%s]_%d.dot", 366 name, 367 pos.getStartPosition(), 368 rsContext.attrMode(), 369 rsContext.step, 370 round); 371 Path dotFile = Paths.get(dependenciesFolder, filename); 372 try (Writer w = Files.newBufferedWriter(dotFile)) { 373 w.append(graph); 374 } 375 round++; 376 } 377 } catch (IOException ex) { 378 Assert.error("Error occurred when dumping inference graph: " + ex.getMessage()); 379 } finally { 380 pendingGraphs = List.nil(); 381 } 382 } 383 384 /** 385 * Generate constraints from the generic method's return type. If the method 386 * call occurs in a context where a type T is expected, use the expected 387 * type to derive more constraints on the generic method inference variables. 388 */ 389 Type generateReturnConstraints(JCTree tree, Attr.ResultInfo resultInfo, 390 MethodType mt, InferenceContext inferenceContext) { 391 InferenceContext rsInfoInfContext = resultInfo.checkContext.inferenceContext(); 392 Type from = mt.getReturnType(); 393 if (mt.getReturnType().containsAny(inferenceContext.inferencevars) && 394 rsInfoInfContext != emptyContext) { 395 from = types.capture(from); 396 //add synthetic captured ivars 397 for (Type t : from.getTypeArguments()) { 398 if (t.hasTag(TYPEVAR) && ((TypeVar)t).isCaptured()) { 399 inferenceContext.addVar((TypeVar)t); 400 } 401 } 402 } 403 Type qtype = inferenceContext.asUndetVar(from); 404 Type to = resultInfo.pt; 405 406 if (qtype.hasTag(VOID)) { 407 to = syms.voidType; 408 } else if (to.hasTag(NONE)) { 409 to = from.isPrimitive() ? from : syms.objectType; 410 } else if (qtype.hasTag(UNDETVAR)) { 411 if (needsEagerInstantiation((UndetVar)qtype, to, inferenceContext) && 412 (allowGraphInference || !to.isPrimitive())) { 413 to = generateReferenceToTargetConstraint(tree, (UndetVar)qtype, to, resultInfo, inferenceContext); 414 } else if (to.isPrimitive()) { 415 to = types.boxedClass(to).type; 416 } 417 } else if (rsInfoInfContext.free(resultInfo.pt)) { 418 //propagation - cache captured vars 419 qtype = inferenceContext.asUndetVar(rsInfoInfContext.cachedCapture(tree, from, false)); 420 } 421 Assert.check(allowGraphInference || !rsInfoInfContext.free(to), 422 "legacy inference engine cannot handle constraints on both sides of a subtyping assertion"); 423 //we need to skip capture? 424 Warner retWarn = new Warner(); 425 if (!resultInfo.checkContext.compatible(qtype, rsInfoInfContext.asUndetVar(to), retWarn) || 426 //unchecked conversion is not allowed in source 7 mode 427 (!allowGraphInference && retWarn.hasLint(Lint.LintCategory.UNCHECKED))) { 428 throw inferenceException 429 .setMessage("infer.no.conforming.instance.exists", 430 inferenceContext.restvars(), mt.getReturnType(), to); 431 } 432 return from; 433 } 434 435 private boolean needsEagerInstantiation(UndetVar from, Type to, InferenceContext inferenceContext) { 436 if (to.isPrimitive()) { 437 /* T is a primitive type, and one of the primitive wrapper classes is an instantiation, 438 * upper bound, or lower bound for alpha in B2. 439 */ 440 for (Type t : from.getBounds(InferenceBound.values())) { 441 Type boundAsPrimitive = types.unboxedType(t); 442 if (boundAsPrimitive == null || boundAsPrimitive.hasTag(NONE)) { 443 continue; 444 } 445 return true; 446 } 447 return false; 448 } 449 450 Type captureOfTo = types.capture(to); 451 /* T is a reference type, but is not a wildcard-parameterized type, and either 452 */ 453 if (captureOfTo == to) { //not a wildcard parameterized type 454 /* i) B2 contains a bound of one of the forms alpha = S or S <: alpha, 455 * where S is a wildcard-parameterized type, or 456 */ 457 for (Type t : from.getBounds(InferenceBound.EQ, InferenceBound.LOWER)) { 458 Type captureOfBound = types.capture(t); 459 if (captureOfBound != t) { 460 return true; 461 } 462 } 463 464 /* ii) B2 contains two bounds of the forms S1 <: alpha and S2 <: alpha, 465 * where S1 and S2 have supertypes that are two different 466 * parameterizations of the same generic class or interface. 467 */ 468 for (Type aLowerBound : from.getBounds(InferenceBound.LOWER)) { 469 for (Type anotherLowerBound : from.getBounds(InferenceBound.LOWER)) { 470 if (aLowerBound != anotherLowerBound && 471 !inferenceContext.free(aLowerBound) && 472 !inferenceContext.free(anotherLowerBound) && 473 commonSuperWithDiffParameterization(aLowerBound, anotherLowerBound)) { 474 return true; 475 } 476 } 477 } 478 } 479 480 /* T is a parameterization of a generic class or interface, G, 481 * and B2 contains a bound of one of the forms alpha = S or S <: alpha, 482 * where there exists no type of the form G<...> that is a 483 * supertype of S, but the raw type G is a supertype of S 484 */ 485 if (to.isParameterized()) { 486 for (Type t : from.getBounds(InferenceBound.EQ, InferenceBound.LOWER)) { 487 Type sup = types.asSuper(t, to.tsym); 488 if (sup != null && sup.isRaw()) { 489 return true; 490 } 491 } 492 } 493 return false; 494 } 495 496 private boolean commonSuperWithDiffParameterization(Type t, Type s) { 497 for (Pair<Type, Type> supers : getParameterizedSupers(t, s)) { 498 if (!types.isSameType(supers.fst, supers.snd)) return true; 499 } 500 return false; 501 } 502 503 private Type generateReferenceToTargetConstraint(JCTree tree, UndetVar from, 504 Type to, Attr.ResultInfo resultInfo, 505 InferenceContext inferenceContext) { 506 inferenceContext.solve(List.of(from.qtype), new Warner()); 507 inferenceContext.notifyChange(); 508 Type capturedType = resultInfo.checkContext.inferenceContext() 509 .cachedCapture(tree, from.getInst(), false); 510 if (types.isConvertible(capturedType, 511 resultInfo.checkContext.inferenceContext().asUndetVar(to))) { 512 //effectively skip additional return-type constraint generation (compatibility) 513 return syms.objectType; 514 } 515 return to; 516 } 517 518 /** 519 * Infer cyclic inference variables as described in 15.12.2.8. 520 */ 521 void instantiateAsUninferredVars(List<Type> vars, InferenceContext inferenceContext) { 522 ListBuffer<Type> todo = new ListBuffer<>(); 523 //step 1 - create fresh tvars 524 for (Type t : vars) { 525 UndetVar uv = (UndetVar)inferenceContext.asUndetVar(t); 526 List<Type> upperBounds = uv.getBounds(InferenceBound.UPPER); 527 if (Type.containsAny(upperBounds, vars)) { 528 TypeSymbol fresh_tvar = new TypeVariableSymbol(Flags.SYNTHETIC, uv.qtype.tsym.name, null, uv.qtype.tsym.owner); 529 fresh_tvar.type = new TypeVar(fresh_tvar, types.makeIntersectionType(uv.getBounds(InferenceBound.UPPER)), null); 530 todo.append(uv); 531 uv.setInst(fresh_tvar.type); 532 } else if (upperBounds.nonEmpty()) { 533 uv.setInst(types.glb(upperBounds)); 534 } else { 535 uv.setInst(syms.objectType); 536 } 537 } 538 //step 2 - replace fresh tvars in their bounds 539 List<Type> formals = vars; 540 for (Type t : todo) { 541 UndetVar uv = (UndetVar)t; 542 TypeVar ct = (TypeVar)uv.getInst(); 543 ct.bound = types.glb(inferenceContext.asInstTypes(types.getBounds(ct))); 544 if (ct.bound.isErroneous()) { 545 //report inference error if glb fails 546 reportBoundError(uv, InferenceBound.UPPER); 547 } 548 formals = formals.tail; 549 } 550 } 551 552 /** 553 * Compute a synthetic method type corresponding to the requested polymorphic 554 * method signature. The target return type is computed from the immediately 555 * enclosing scope surrounding the polymorphic-signature call. 556 */ 557 Type instantiatePolymorphicSignatureInstance(Env<AttrContext> env, 558 MethodSymbol spMethod, // sig. poly. method or null if none 559 Resolve.MethodResolutionContext resolveContext, 560 List<Type> argtypes) { 561 final Type restype; 562 563 if (spMethod == null || types.isSameType(spMethod.getReturnType(), syms.objectType, true)) { 564 // The return type of the polymorphic signature is polymorphic, 565 // and is computed from the enclosing tree E, as follows: 566 // if E is a cast, then use the target type of the cast expression 567 // as a return type; if E is an expression statement, the return 568 // type is 'void'; otherwise 569 // the return type is simply 'Object'. A correctness check ensures 570 // that env.next refers to the lexically enclosing environment in 571 // which the polymorphic signature call environment is nested. 572 573 switch (env.next.tree.getTag()) { 574 case TYPECAST: 575 JCTypeCast castTree = (JCTypeCast)env.next.tree; 576 restype = (TreeInfo.skipParens(castTree.expr) == env.tree) ? 577 castTree.clazz.type : 578 syms.objectType; 579 break; 580 case EXEC: 581 JCTree.JCExpressionStatement execTree = 582 (JCTree.JCExpressionStatement)env.next.tree; 583 restype = (TreeInfo.skipParens(execTree.expr) == env.tree) ? 584 syms.voidType : 585 syms.objectType; 586 break; 587 default: 588 restype = syms.objectType; 589 } 590 } else { 591 // The return type of the polymorphic signature is fixed 592 // (not polymorphic) 593 restype = spMethod.getReturnType(); 594 } 595 596 List<Type> paramtypes = argtypes.map(new ImplicitArgType(spMethod, resolveContext.step)); 597 List<Type> exType = spMethod != null ? 598 spMethod.getThrownTypes() : 599 List.of(syms.throwableType); // make it throw all exceptions 600 601 MethodType mtype = new MethodType(paramtypes, 602 restype, 603 exType, 604 syms.methodClass); 605 return mtype; 606 } 607 //where 608 class ImplicitArgType extends DeferredAttr.DeferredTypeMap { 609 610 public ImplicitArgType(Symbol msym, Resolve.MethodResolutionPhase phase) { 611 (rs.deferredAttr).super(AttrMode.SPECULATIVE, msym, phase); 612 } 613 614 @Override 615 public Type visitClassType(ClassType t, Void aVoid) { 616 return types.erasure(t); 617 } 618 619 @Override 620 public Type visitType(Type t, Void _unused) { 621 if (t.hasTag(DEFERRED)) { 622 return visit(super.visitType(t, null)); 623 } else if (t.hasTag(BOT)) 624 // nulls type as the marker type Null (which has no instances) 625 // infer as java.lang.Void for now 626 t = types.boxedClass(syms.voidType).type; 627 return t; 628 } 629 } 630 631 TypeMapping<Void> fromTypeVarFun = new TypeMapping<Void>() { 632 @Override 633 public Type visitTypeVar(TypeVar tv, Void aVoid) { 634 UndetVar uv = new UndetVar(tv, incorporationEngine(), types); 635 if ((tv.tsym.flags() & Flags.THROWS) != 0) { 636 uv.setThrow(); 637 } 638 return uv; 639 } 640 }; 641 642 /** 643 * This method is used to infer a suitable target SAM in case the original 644 * SAM type contains one or more wildcards. An inference process is applied 645 * so that wildcard bounds, as well as explicit lambda/method ref parameters 646 * (where applicable) are used to constraint the solution. 647 */ 648 public Type instantiateFunctionalInterface(DiagnosticPosition pos, Type funcInterface, 649 List<Type> paramTypes, Check.CheckContext checkContext) { 650 if (types.capture(funcInterface) == funcInterface) { 651 //if capture doesn't change the type then return the target unchanged 652 //(this means the target contains no wildcards!) 653 return funcInterface; 654 } else { 655 Type formalInterface = funcInterface.tsym.type; 656 InferenceContext funcInterfaceContext = 657 new InferenceContext(this, funcInterface.tsym.type.getTypeArguments()); 658 659 Assert.check(paramTypes != null); 660 //get constraints from explicit params (this is done by 661 //checking that explicit param types are equal to the ones 662 //in the functional interface descriptors) 663 List<Type> descParameterTypes = types.findDescriptorType(formalInterface).getParameterTypes(); 664 if (descParameterTypes.size() != paramTypes.size()) { 665 checkContext.report(pos, diags.fragment("incompatible.arg.types.in.lambda")); 666 return types.createErrorType(funcInterface); 667 } 668 for (Type p : descParameterTypes) { 669 if (!types.isSameType(funcInterfaceContext.asUndetVar(p), paramTypes.head)) { 670 checkContext.report(pos, diags.fragment("no.suitable.functional.intf.inst", funcInterface)); 671 return types.createErrorType(funcInterface); 672 } 673 paramTypes = paramTypes.tail; 674 } 675 676 List<Type> actualTypeargs = funcInterface.getTypeArguments(); 677 for (Type t : funcInterfaceContext.undetvars) { 678 UndetVar uv = (UndetVar)t; 679 Optional<Type> inst = uv.getBounds(InferenceBound.EQ).stream() 680 .filter(b -> !b.containsAny(formalInterface.getTypeArguments())).findFirst(); 681 uv.setInst(inst.orElse(actualTypeargs.head)); 682 actualTypeargs = actualTypeargs.tail; 683 } 684 685 Type owntype = funcInterfaceContext.asInstType(formalInterface); 686 if (!chk.checkValidGenericType(owntype)) { 687 //if the inferred functional interface type is not well-formed, 688 //or if it's not a subtype of the original target, issue an error 689 checkContext.report(pos, diags.fragment("no.suitable.functional.intf.inst", funcInterface)); 690 } 691 //propagate constraints as per JLS 18.2.1 692 checkContext.compatible(owntype, funcInterface, types.noWarnings); 693 return owntype; 694 } 695 } 696 // </editor-fold> 697 698 // <editor-fold defaultstate="collapsed" desc="Incorporation"> 699 700 /** 701 * This class is the root of all incorporation actions. 702 */ 703 public abstract class IncorporationAction { 704 UndetVar uv; 705 Type t; 706 707 IncorporationAction(UndetVar uv, Type t) { 708 this.uv = uv; 709 this.t = t; 710 } 711 712 public abstract IncorporationAction dup(UndetVar that); 713 714 /** 715 * Incorporation action entry-point. Subclasses should define the logic associated with 716 * this incorporation action. 717 */ 718 abstract void apply(InferenceContext ic, Warner warn); 719 720 /** 721 * Helper function: perform subtyping through incorporation cache. 722 */ 723 boolean isSubtype(Type s, Type t, Warner warn) { 724 return doIncorporationOp(IncorporationBinaryOpKind.IS_SUBTYPE, s, t, warn); 725 } 726 727 /** 728 * Helper function: perform type-equivalence through incorporation cache. 729 */ 730 boolean isSameType(Type s, Type t) { 731 return doIncorporationOp(IncorporationBinaryOpKind.IS_SAME_TYPE, s, t, null); 732 } 733 734 @Override 735 public String toString() { 736 return String.format("%s[undet=%s,t=%s]", getClass().getSimpleName(), uv.qtype, t); 737 } 738 } 739 740 /** 741 * Bound-check incorporation action. A newly added bound is checked against existing bounds, 742 * to verify its compatibility; each bound is checked using either subtyping or type equivalence. 743 */ 744 class CheckBounds extends IncorporationAction { 745 746 InferenceBound from; 747 BiFunction<InferenceContext, Type, Type> typeFunc; 748 BiPredicate<InferenceContext, Type> optFilter; 749 750 CheckBounds(UndetVar uv, Type t, InferenceBound from) { 751 this(uv, t, InferenceContext::asUndetVar, null, from); 752 } 753 754 CheckBounds(UndetVar uv, Type t, BiFunction<InferenceContext, Type, Type> typeFunc, 755 BiPredicate<InferenceContext, Type> typeFilter, InferenceBound from) { 756 super(uv, t); 757 this.from = from; 758 this.typeFunc = typeFunc; 759 this.optFilter = typeFilter; 760 } 761 762 @Override 763 public IncorporationAction dup(UndetVar that) { 764 return new CheckBounds(that, t, typeFunc, optFilter, from); 765 } 766 767 @Override 768 void apply(InferenceContext inferenceContext, Warner warn) { 769 t = typeFunc.apply(inferenceContext, t); 770 if (optFilter != null && optFilter.test(inferenceContext, t)) return; 771 for (InferenceBound to : boundsToCheck()) { 772 for (Type b : uv.getBounds(to)) { 773 b = typeFunc.apply(inferenceContext, b); 774 if (optFilter != null && optFilter.test(inferenceContext, b)) continue; 775 boolean success = checkBound(t, b, from, to, warn); 776 if (!success) { 777 report(from, to); 778 } 779 } 780 } 781 } 782 783 /** 784 * The list of bound kinds to be checked. 785 */ 786 EnumSet<InferenceBound> boundsToCheck() { 787 return (from == InferenceBound.EQ) ? 788 EnumSet.allOf(InferenceBound.class) : 789 EnumSet.complementOf(EnumSet.of(from)); 790 } 791 792 /** 793 * Is source type 's' compatible with target type 't' given source and target bound kinds? 794 */ 795 boolean checkBound(Type s, Type t, InferenceBound ib_s, InferenceBound ib_t, Warner warn) { 796 if (ib_s.lessThan(ib_t)) { 797 return isSubtype(s, t, warn); 798 } else if (ib_t.lessThan(ib_s)) { 799 return isSubtype(t, s, warn); 800 } else { 801 return isSameType(s, t); 802 } 803 } 804 805 /** 806 * Report a bound check error. 807 */ 808 void report(InferenceBound from, InferenceBound to) { 809 //this is a workaround to preserve compatibility with existing messages 810 if (from == to) { 811 reportBoundError(uv, from); 812 } else if (from == InferenceBound.LOWER || to == InferenceBound.EQ) { 813 reportBoundError(uv, to, from); 814 } else { 815 reportBoundError(uv, from, to); 816 } 817 } 818 819 @Override 820 public String toString() { 821 return String.format("%s[undet=%s,t=%s,bound=%s]", getClass().getSimpleName(), uv.qtype, t, from); 822 } 823 } 824 825 /** 826 * Custom check executed by the legacy incorporation engine. Newly added bounds are checked 827 * against existing eq bounds. 828 */ 829 class EqCheckLegacy extends CheckBounds { 830 EqCheckLegacy(UndetVar uv, Type t, InferenceBound from) { 831 super(uv, t, InferenceContext::asInstType, InferenceContext::free, from); 832 } 833 834 @Override 835 public IncorporationAction dup(UndetVar that) { 836 return new EqCheckLegacy(that, t, from); 837 } 838 839 @Override 840 EnumSet<InferenceBound> boundsToCheck() { 841 return (from == InferenceBound.EQ) ? 842 EnumSet.allOf(InferenceBound.class) : 843 EnumSet.of(InferenceBound.EQ); 844 } 845 } 846 847 /** 848 * Check that the inferred type conforms to all bounds. 849 */ 850 class CheckInst extends CheckBounds { 851 852 EnumSet<InferenceBound> to; 853 854 CheckInst(UndetVar uv, InferenceBound ib, InferenceBound... rest) { 855 this(uv, EnumSet.of(ib, rest)); 856 } 857 858 CheckInst(UndetVar uv, EnumSet<InferenceBound> to) { 859 super(uv, uv.getInst(), InferenceBound.EQ); 860 this.to = to; 861 } 862 863 @Override 864 public IncorporationAction dup(UndetVar that) { 865 return new CheckInst(that, to); 866 } 867 868 @Override 869 EnumSet<InferenceBound> boundsToCheck() { 870 return to; 871 } 872 873 @Override 874 void report(InferenceBound from, InferenceBound to) { 875 reportInstError(uv, to); 876 } 877 } 878 879 /** 880 * Replace undetvars in bounds and check that the inferred type conforms to all bounds. 881 */ 882 class SubstBounds extends CheckInst { 883 SubstBounds(UndetVar uv) { 884 super(uv, InferenceBound.LOWER, InferenceBound.EQ, InferenceBound.UPPER); 885 } 886 887 @Override 888 public IncorporationAction dup(UndetVar that) { 889 return new SubstBounds(that); 890 } 891 892 @Override 893 void apply(InferenceContext inferenceContext, Warner warn) { 894 for (Type undet : inferenceContext.undetvars) { 895 //we could filter out variables not mentioning uv2... 896 UndetVar uv2 = (UndetVar)undet; 897 uv2.substBounds(List.of(uv.qtype), List.of(uv.getInst()), types); 898 checkCompatibleUpperBounds(uv2, inferenceContext); 899 } 900 super.apply(inferenceContext, warn); 901 } 902 903 /** 904 * Make sure that the upper bounds we got so far lead to a solvable inference 905 * variable by making sure that a glb exists. 906 */ 907 void checkCompatibleUpperBounds(UndetVar uv, InferenceContext inferenceContext) { 908 List<Type> hibounds = 909 Type.filter(uv.getBounds(InferenceBound.UPPER), new BoundFilter(inferenceContext)); 910 final Type hb; 911 if (hibounds.isEmpty()) 912 hb = syms.objectType; 913 else if (hibounds.tail.isEmpty()) 914 hb = hibounds.head; 915 else 916 hb = types.glb(hibounds); 917 if (hb == null || hb.isErroneous()) 918 reportBoundError(uv, InferenceBound.UPPER); 919 } 920 } 921 922 /** 923 * Perform pairwise comparison between common generic supertypes of two upper bounds. 924 */ 925 class CheckUpperBounds extends IncorporationAction { 926 927 public CheckUpperBounds(UndetVar uv, Type t) { 928 super(uv, t); 929 } 930 931 @Override 932 public IncorporationAction dup(UndetVar that) { 933 return new CheckUpperBounds(that, t); 934 } 935 936 @Override 937 void apply(InferenceContext inferenceContext, Warner warn) { 938 List<Type> boundList = uv.getBounds(InferenceBound.UPPER).stream() 939 .collect(types.closureCollector(true, types::isSameType)); 940 for (Type b2 : boundList) { 941 if (t == b2) continue; 942 /* This wildcard check is temporary workaround. This code may need to be 943 * revisited once spec bug JDK-7034922 is fixed. 944 */ 945 if (t != b2 && !t.hasTag(WILDCARD) && !b2.hasTag(WILDCARD)) { 946 for (Pair<Type, Type> commonSupers : getParameterizedSupers(t, b2)) { 947 List<Type> allParamsSuperBound1 = commonSupers.fst.allparams(); 948 List<Type> allParamsSuperBound2 = commonSupers.snd.allparams(); 949 while (allParamsSuperBound1.nonEmpty() && allParamsSuperBound2.nonEmpty()) { 950 //traverse the list of all params comparing them 951 if (!allParamsSuperBound1.head.hasTag(WILDCARD) && 952 !allParamsSuperBound2.head.hasTag(WILDCARD)) { 953 if (!isSameType(inferenceContext.asUndetVar(allParamsSuperBound1.head), 954 inferenceContext.asUndetVar(allParamsSuperBound2.head))) { 955 reportBoundError(uv, InferenceBound.UPPER); 956 } 957 } 958 allParamsSuperBound1 = allParamsSuperBound1.tail; 959 allParamsSuperBound2 = allParamsSuperBound2.tail; 960 } 961 Assert.check(allParamsSuperBound1.isEmpty() && allParamsSuperBound2.isEmpty()); 962 } 963 } 964 } 965 } 966 } 967 968 /** 969 * Perform propagation of bounds. Given a constraint of the kind {@code alpha <: T}, three 970 * kind of propagation occur: 971 * 972 * <li>T is copied into all matching bounds (i.e. lower/eq bounds) B of alpha such that B=beta (forward propagation)</li> 973 * <li>if T=beta, matching bounds (i.e. upper bounds) of beta are copied into alpha (backwards propagation)</li> 974 * <li>if T=beta, sets a symmetric bound on beta (i.e. beta :> alpha) (symmetric propagation) </li> 975 */ 976 class PropagateBounds extends IncorporationAction { 977 978 InferenceBound ib; 979 980 public PropagateBounds(UndetVar uv, Type t, InferenceBound ib) { 981 super(uv, t); 982 this.ib = ib; 983 } 984 985 @Override 986 public IncorporationAction dup(UndetVar that) { 987 return new PropagateBounds(that, t, ib); 988 } 989 990 void apply(InferenceContext inferenceContext, Warner warner) { 991 Type undetT = inferenceContext.asUndetVar(t); 992 if (undetT.hasTag(UNDETVAR) && !((UndetVar)undetT).isCaptured()) { 993 UndetVar uv2 = (UndetVar)undetT; 994 //symmetric propagation 995 uv2.addBound(ib.complement(), uv, types); 996 //backwards propagation 997 for (InferenceBound ib2 : backwards()) { 998 for (Type b : uv2.getBounds(ib2)) { 999 uv.addBound(ib2, b, types); 1000 } 1001 } 1002 } 1003 //forward propagation 1004 for (InferenceBound ib2 : forward()) { 1005 for (Type l : uv.getBounds(ib2)) { 1006 Type undet = inferenceContext.asUndetVar(l); 1007 if (undet.hasTag(TypeTag.UNDETVAR) && !((UndetVar)undet).isCaptured()) { 1008 UndetVar uv2 = (UndetVar)undet; 1009 uv2.addBound(ib, inferenceContext.asInstType(t), types); 1010 } 1011 } 1012 } 1013 } 1014 1015 EnumSet<InferenceBound> forward() { 1016 return (ib == InferenceBound.EQ) ? 1017 EnumSet.of(InferenceBound.EQ) : EnumSet.complementOf(EnumSet.of(ib)); 1018 } 1019 1020 EnumSet<InferenceBound> backwards() { 1021 return (ib == InferenceBound.EQ) ? 1022 EnumSet.allOf(InferenceBound.class) : EnumSet.of(ib); 1023 } 1024 1025 @Override 1026 public String toString() { 1027 return String.format("%s[undet=%s,t=%s,bound=%s]", getClass().getSimpleName(), uv.qtype, t, ib); 1028 } 1029 } 1030 1031 /** 1032 * This class models an incorporation engine. The engine is responsible for listening to 1033 * changes in inference variables and register incorporation actions accordingly. 1034 */ 1035 abstract class AbstractIncorporationEngine implements UndetVarListener { 1036 1037 @Override 1038 public void varInstantiated(UndetVar uv) { 1039 uv.incorporationActions.addFirst(new SubstBounds(uv)); 1040 } 1041 1042 @Override 1043 public void varBoundChanged(UndetVar uv, InferenceBound ib, Type bound, boolean update) { 1044 if (uv.isCaptured()) return; 1045 uv.incorporationActions.addAll(getIncorporationActions(uv, ib, bound, update)); 1046 } 1047 1048 abstract List<IncorporationAction> getIncorporationActions(UndetVar uv, InferenceBound ib, Type t, boolean update); 1049 } 1050 1051 /** 1052 * A legacy incorporation engine. Used for source <= 7. 1053 */ 1054 AbstractIncorporationEngine legacyEngine = new AbstractIncorporationEngine() { 1055 1056 List<IncorporationAction> getIncorporationActions(UndetVar uv, InferenceBound ib, Type t, boolean update) { 1057 ListBuffer<IncorporationAction> actions = new ListBuffer<>(); 1058 Type inst = uv.getInst(); 1059 if (inst != null) { 1060 actions.add(new CheckInst(uv, ib)); 1061 } 1062 actions.add(new EqCheckLegacy(uv, t, ib)); 1063 return actions.toList(); 1064 } 1065 }; 1066 1067 /** 1068 * The standard incorporation engine. Used for source >= 8. 1069 */ 1070 AbstractIncorporationEngine graphEngine = new AbstractIncorporationEngine() { 1071 1072 @Override 1073 List<IncorporationAction> getIncorporationActions(UndetVar uv, InferenceBound ib, Type t, boolean update) { 1074 ListBuffer<IncorporationAction> actions = new ListBuffer<>(); 1075 Type inst = uv.getInst(); 1076 if (inst != null) { 1077 actions.add(new CheckInst(uv, ib)); 1078 } 1079 actions.add(new CheckBounds(uv, t, ib)); 1080 1081 if (update) { 1082 return actions.toList(); 1083 } 1084 1085 if (ib == InferenceBound.UPPER) { 1086 actions.add(new CheckUpperBounds(uv, t)); 1087 } 1088 1089 actions.add(new PropagateBounds(uv, t, ib)); 1090 1091 return actions.toList(); 1092 } 1093 }; 1094 1095 /** 1096 * Get the incorporation engine to be used in this compilation. 1097 */ 1098 AbstractIncorporationEngine incorporationEngine() { 1099 return allowGraphInference ? graphEngine : legacyEngine; 1100 } 1101 1102 /** max number of incorporation rounds. */ 1103 static final int MAX_INCORPORATION_STEPS = 10000; 1104 1105 /** 1106 * Check bounds and perform incorporation. 1107 */ 1108 void doIncorporation(InferenceContext inferenceContext, Warner warn) throws InferenceException { 1109 try { 1110 boolean progress = true; 1111 int round = 0; 1112 while (progress && round < MAX_INCORPORATION_STEPS) { 1113 progress = false; 1114 for (Type t : inferenceContext.undetvars) { 1115 UndetVar uv = (UndetVar)t; 1116 if (!uv.incorporationActions.isEmpty()) { 1117 progress = true; 1118 uv.incorporationActions.removeFirst().apply(inferenceContext, warn); 1119 } 1120 } 1121 round++; 1122 } 1123 } finally { 1124 incorporationCache.clear(); 1125 } 1126 } 1127 1128 /* If for two types t and s there is a least upper bound that contains 1129 * parameterized types G1, G2 ... Gn, then there exists supertypes of 't' of the form 1130 * G1<T1, ..., Tn>, G2<T1, ..., Tn>, ... Gn<T1, ..., Tn> and supertypes of 's' of the form 1131 * G1<S1, ..., Sn>, G2<S1, ..., Sn>, ... Gn<S1, ..., Sn> which will be returned by this method. 1132 * If no such common supertypes exists then an empty list is returned. 1133 * 1134 * As an example for the following input: 1135 * 1136 * t = java.util.ArrayList<java.lang.String> 1137 * s = java.util.List<T> 1138 * 1139 * we get this ouput (singleton list): 1140 * 1141 * [Pair[java.util.List<java.lang.String>,java.util.List<T>]] 1142 */ 1143 private List<Pair<Type, Type>> getParameterizedSupers(Type t, Type s) { 1144 Type lubResult = types.lub(t, s); 1145 if (lubResult == syms.errType || lubResult == syms.botType) { 1146 return List.nil(); 1147 } 1148 List<Type> supertypesToCheck = lubResult.isIntersection() ? 1149 ((IntersectionClassType)lubResult).getComponents() : 1150 List.of(lubResult); 1151 ListBuffer<Pair<Type, Type>> commonSupertypes = new ListBuffer<>(); 1152 for (Type sup : supertypesToCheck) { 1153 if (sup.isParameterized()) { 1154 Type asSuperOfT = asSuper(t, sup); 1155 Type asSuperOfS = asSuper(s, sup); 1156 commonSupertypes.add(new Pair<>(asSuperOfT, asSuperOfS)); 1157 } 1158 } 1159 return commonSupertypes.toList(); 1160 } 1161 //where 1162 private Type asSuper(Type t, Type sup) { 1163 return (sup.hasTag(ARRAY)) ? 1164 new ArrayType(asSuper(types.elemtype(t), types.elemtype(sup)), syms.arrayClass) : 1165 types.asSuper(t, sup.tsym); 1166 } 1167 1168 boolean doIncorporationOp(IncorporationBinaryOpKind opKind, Type op1, Type op2, Warner warn) { 1169 IncorporationBinaryOp newOp = new IncorporationBinaryOp(opKind, op1, op2); 1170 Boolean res = incorporationCache.get(newOp); 1171 if (res == null) { 1172 incorporationCache.put(newOp, res = newOp.apply(warn)); 1173 } 1174 return res; 1175 } 1176 1177 /** 1178 * Three kinds of basic operation are supported as part of an incorporation step: 1179 * (i) subtype check, (ii) same type check and (iii) bound addition (either 1180 * upper/lower/eq bound). 1181 */ 1182 enum IncorporationBinaryOpKind { 1183 IS_SUBTYPE() { 1184 @Override 1185 boolean apply(Type op1, Type op2, Warner warn, Types types) { 1186 return types.isSubtypeUnchecked(op1, op2, warn); 1187 } 1188 }, 1189 IS_SAME_TYPE() { 1190 @Override 1191 boolean apply(Type op1, Type op2, Warner warn, Types types) { 1192 return types.isSameType(op1, op2); 1193 } 1194 }; 1195 1196 abstract boolean apply(Type op1, Type op2, Warner warn, Types types); 1197 } 1198 1199 /** 1200 * This class encapsulates a basic incorporation operation; incorporation 1201 * operations takes two type operands and a kind. Each operation performed 1202 * during an incorporation round is stored in a cache, so that operations 1203 * are not executed unnecessarily (which would potentially lead to adding 1204 * same bounds over and over). 1205 */ 1206 class IncorporationBinaryOp { 1207 1208 IncorporationBinaryOpKind opKind; 1209 Type op1; 1210 Type op2; 1211 1212 IncorporationBinaryOp(IncorporationBinaryOpKind opKind, Type op1, Type op2) { 1213 this.opKind = opKind; 1214 this.op1 = op1; 1215 this.op2 = op2; 1216 } 1217 1218 @Override 1219 public boolean equals(Object o) { 1220 if (!(o instanceof IncorporationBinaryOp)) { 1221 return false; 1222 } else { 1223 IncorporationBinaryOp that = (IncorporationBinaryOp)o; 1224 return opKind == that.opKind && 1225 types.isSameType(op1, that.op1, true) && 1226 types.isSameType(op2, that.op2, true); 1227 } 1228 } 1229 1230 @Override 1231 public int hashCode() { 1232 int result = opKind.hashCode(); 1233 result *= 127; 1234 result += types.hashCode(op1); 1235 result *= 127; 1236 result += types.hashCode(op2); 1237 return result; 1238 } 1239 1240 boolean apply(Warner warn) { 1241 return opKind.apply(op1, op2, warn, types); 1242 } 1243 } 1244 1245 /** an incorporation cache keeps track of all executed incorporation-related operations */ 1246 Map<IncorporationBinaryOp, Boolean> incorporationCache = new HashMap<>(); 1247 1248 protected static class BoundFilter implements Filter<Type> { 1249 1250 InferenceContext inferenceContext; 1251 1252 public BoundFilter(InferenceContext inferenceContext) { 1253 this.inferenceContext = inferenceContext; 1254 } 1255 1256 @Override 1257 public boolean accepts(Type t) { 1258 return !t.isErroneous() && !inferenceContext.free(t) && 1259 !t.hasTag(BOT); 1260 } 1261 } 1262 1263 /** 1264 * Incorporation error: mismatch between inferred type and given bound. 1265 */ 1266 void reportInstError(UndetVar uv, InferenceBound ib) { 1267 reportInferenceError( 1268 String.format("inferred.do.not.conform.to.%s.bounds", StringUtils.toLowerCase(ib.name())), 1269 uv.getInst(), 1270 uv.getBounds(ib)); 1271 } 1272 1273 /** 1274 * Incorporation error: mismatch between two (or more) bounds of same kind. 1275 */ 1276 void reportBoundError(UndetVar uv, InferenceBound ib) { 1277 reportInferenceError( 1278 String.format("incompatible.%s.bounds", StringUtils.toLowerCase(ib.name())), 1279 uv.qtype, 1280 uv.getBounds(ib)); 1281 } 1282 1283 /** 1284 * Incorporation error: mismatch between two (or more) bounds of different kinds. 1285 */ 1286 void reportBoundError(UndetVar uv, InferenceBound ib1, InferenceBound ib2) { 1287 reportInferenceError( 1288 String.format("incompatible.%s.%s.bounds", 1289 StringUtils.toLowerCase(ib1.name()), 1290 StringUtils.toLowerCase(ib2.name())), 1291 uv.qtype, 1292 uv.getBounds(ib1), 1293 uv.getBounds(ib2)); 1294 } 1295 1296 /** 1297 * Helper method: reports an inference error. 1298 */ 1299 void reportInferenceError(String key, Object... args) { 1300 throw inferenceException.setMessage(key, args); 1301 } 1302 // </editor-fold> 1303 1304 // <editor-fold defaultstate="collapsed" desc="Inference engine"> 1305 /** 1306 * Graph inference strategy - act as an input to the inference solver; a strategy is 1307 * composed of two ingredients: (i) find a node to solve in the inference graph, 1308 * and (ii) tell th engine when we are done fixing inference variables 1309 */ 1310 interface GraphStrategy { 1311 1312 /** 1313 * A NodeNotFoundException is thrown whenever an inference strategy fails 1314 * to pick the next node to solve in the inference graph. 1315 */ 1316 public static class NodeNotFoundException extends RuntimeException { 1317 private static final long serialVersionUID = 0; 1318 1319 InferenceGraph graph; 1320 1321 public NodeNotFoundException(InferenceGraph graph) { 1322 this.graph = graph; 1323 } 1324 } 1325 /** 1326 * Pick the next node (leaf) to solve in the graph 1327 */ 1328 Node pickNode(InferenceGraph g) throws NodeNotFoundException; 1329 /** 1330 * Is this the last step? 1331 */ 1332 boolean done(); 1333 } 1334 1335 /** 1336 * Simple solver strategy class that locates all leaves inside a graph 1337 * and picks the first leaf as the next node to solve 1338 */ 1339 abstract class LeafSolver implements GraphStrategy { 1340 public Node pickNode(InferenceGraph g) { 1341 if (g.nodes.isEmpty()) { 1342 //should not happen 1343 throw new NodeNotFoundException(g); 1344 } 1345 return g.nodes.get(0); 1346 } 1347 } 1348 1349 /** 1350 * This solver uses an heuristic to pick the best leaf - the heuristic 1351 * tries to select the node that has maximal probability to contain one 1352 * or more inference variables in a given list 1353 */ 1354 abstract class BestLeafSolver extends LeafSolver { 1355 1356 /** list of ivars of which at least one must be solved */ 1357 List<Type> varsToSolve; 1358 1359 BestLeafSolver(List<Type> varsToSolve) { 1360 this.varsToSolve = varsToSolve; 1361 } 1362 1363 /** 1364 * Computes a path that goes from a given node to the leafs in the graph. 1365 * Typically this will start from a node containing a variable in 1366 * {@code varsToSolve}. For any given path, the cost is computed as the total 1367 * number of type-variables that should be eagerly instantiated across that path. 1368 */ 1369 Pair<List<Node>, Integer> computeTreeToLeafs(Node n) { 1370 Pair<List<Node>, Integer> cachedPath = treeCache.get(n); 1371 if (cachedPath == null) { 1372 //cache miss 1373 if (n.isLeaf()) { 1374 //if leaf, stop 1375 cachedPath = new Pair<>(List.of(n), n.data.length()); 1376 } else { 1377 //if non-leaf, proceed recursively 1378 Pair<List<Node>, Integer> path = new Pair<>(List.of(n), n.data.length()); 1379 for (Node n2 : n.getAllDependencies()) { 1380 if (n2 == n) continue; 1381 Pair<List<Node>, Integer> subpath = computeTreeToLeafs(n2); 1382 path = new Pair<>(path.fst.prependList(subpath.fst), 1383 path.snd + subpath.snd); 1384 } 1385 cachedPath = path; 1386 } 1387 //save results in cache 1388 treeCache.put(n, cachedPath); 1389 } 1390 return cachedPath; 1391 } 1392 1393 /** cache used to avoid redundant computation of tree costs */ 1394 final Map<Node, Pair<List<Node>, Integer>> treeCache = new HashMap<>(); 1395 1396 /** constant value used to mark non-existent paths */ 1397 final Pair<List<Node>, Integer> noPath = new Pair<>(null, Integer.MAX_VALUE); 1398 1399 /** 1400 * Pick the leaf that minimize cost 1401 */ 1402 @Override 1403 public Node pickNode(final InferenceGraph g) { 1404 treeCache.clear(); //graph changes at every step - cache must be cleared 1405 Pair<List<Node>, Integer> bestPath = noPath; 1406 for (Node n : g.nodes) { 1407 if (!Collections.disjoint(n.data, varsToSolve)) { 1408 Pair<List<Node>, Integer> path = computeTreeToLeafs(n); 1409 //discard all paths containing at least a node in the 1410 //closure computed above 1411 if (path.snd < bestPath.snd) { 1412 bestPath = path; 1413 } 1414 } 1415 } 1416 if (bestPath == noPath) { 1417 //no path leads there 1418 throw new NodeNotFoundException(g); 1419 } 1420 return bestPath.fst.head; 1421 } 1422 } 1423 1424 /** 1425 * The inference process can be thought of as a sequence of steps. Each step 1426 * instantiates an inference variable using a subset of the inference variable 1427 * bounds, if certain condition are met. Decisions such as the sequence in which 1428 * steps are applied, or which steps are to be applied are left to the inference engine. 1429 */ 1430 enum InferenceStep { 1431 1432 /** 1433 * Instantiate an inference variables using one of its (ground) equality 1434 * constraints 1435 */ 1436 EQ(InferenceBound.EQ) { 1437 @Override 1438 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1439 return filterBounds(uv, inferenceContext).head; 1440 } 1441 }, 1442 /** 1443 * Instantiate an inference variables using its (ground) lower bounds. Such 1444 * bounds are merged together using lub(). 1445 */ 1446 LOWER(InferenceBound.LOWER) { 1447 @Override 1448 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1449 Infer infer = inferenceContext.infer; 1450 List<Type> lobounds = filterBounds(uv, inferenceContext); 1451 //note: lobounds should have at least one element 1452 Type owntype = lobounds.tail.tail == null ? lobounds.head : infer.types.lub(lobounds); 1453 if (owntype.isPrimitive() || owntype.hasTag(ERROR)) { 1454 throw infer.inferenceException 1455 .setMessage("no.unique.minimal.instance.exists", 1456 uv.qtype, lobounds); 1457 } else { 1458 return owntype; 1459 } 1460 } 1461 }, 1462 /** 1463 * Infer uninstantiated/unbound inference variables occurring in 'throws' 1464 * clause as RuntimeException 1465 */ 1466 THROWS(InferenceBound.UPPER) { 1467 @Override 1468 public boolean accepts(UndetVar t, InferenceContext inferenceContext) { 1469 if (!t.isThrows()) { 1470 //not a throws undet var 1471 return false; 1472 } 1473 Types types = inferenceContext.types; 1474 Symtab syms = inferenceContext.infer.syms; 1475 return t.getBounds(InferenceBound.UPPER).stream() 1476 .filter(b -> !inferenceContext.free(b)) 1477 .allMatch(u -> types.isSubtype(syms.runtimeExceptionType, u)); 1478 } 1479 1480 @Override 1481 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1482 return inferenceContext.infer.syms.runtimeExceptionType; 1483 } 1484 }, 1485 /** 1486 * Instantiate an inference variables using its (ground) upper bounds. Such 1487 * bounds are merged together using glb(). 1488 */ 1489 UPPER(InferenceBound.UPPER) { 1490 @Override 1491 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1492 Infer infer = inferenceContext.infer; 1493 List<Type> hibounds = filterBounds(uv, inferenceContext); 1494 //note: hibounds should have at least one element 1495 Type owntype = hibounds.tail.tail == null ? hibounds.head : infer.types.glb(hibounds); 1496 if (owntype.isPrimitive() || owntype.hasTag(ERROR)) { 1497 throw infer.inferenceException 1498 .setMessage("no.unique.maximal.instance.exists", 1499 uv.qtype, hibounds); 1500 } else { 1501 return owntype; 1502 } 1503 } 1504 }, 1505 /** 1506 * Like the former; the only difference is that this step can only be applied 1507 * if all upper bounds are ground. 1508 */ 1509 UPPER_LEGACY(InferenceBound.UPPER) { 1510 @Override 1511 public boolean accepts(UndetVar t, InferenceContext inferenceContext) { 1512 return !inferenceContext.free(t.getBounds(ib)) && !t.isCaptured(); 1513 } 1514 1515 @Override 1516 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1517 return UPPER.solve(uv, inferenceContext); 1518 } 1519 }, 1520 /** 1521 * Like the former; the only difference is that this step can only be applied 1522 * if all upper/lower bounds are ground. 1523 */ 1524 CAPTURED(InferenceBound.UPPER) { 1525 @Override 1526 public boolean accepts(UndetVar t, InferenceContext inferenceContext) { 1527 return t.isCaptured() && 1528 !inferenceContext.free(t.getBounds(InferenceBound.UPPER, InferenceBound.LOWER)); 1529 } 1530 1531 @Override 1532 Type solve(UndetVar uv, InferenceContext inferenceContext) { 1533 Infer infer = inferenceContext.infer; 1534 Type upper = UPPER.filterBounds(uv, inferenceContext).nonEmpty() ? 1535 UPPER.solve(uv, inferenceContext) : 1536 infer.syms.objectType; 1537 Type lower = LOWER.filterBounds(uv, inferenceContext).nonEmpty() ? 1538 LOWER.solve(uv, inferenceContext) : 1539 infer.syms.botType; 1540 CapturedType prevCaptured = (CapturedType)uv.qtype; 1541 return new CapturedType(prevCaptured.tsym.name, prevCaptured.tsym.owner, 1542 upper, lower, prevCaptured.wildcard); 1543 } 1544 }; 1545 1546 final InferenceBound ib; 1547 1548 InferenceStep(InferenceBound ib) { 1549 this.ib = ib; 1550 } 1551 1552 /** 1553 * Find an instantiated type for a given inference variable within 1554 * a given inference context 1555 */ 1556 abstract Type solve(UndetVar uv, InferenceContext inferenceContext); 1557 1558 /** 1559 * Can the inference variable be instantiated using this step? 1560 */ 1561 public boolean accepts(UndetVar t, InferenceContext inferenceContext) { 1562 return filterBounds(t, inferenceContext).nonEmpty() && !t.isCaptured(); 1563 } 1564 1565 /** 1566 * Return the subset of ground bounds in a given bound set (i.e. eq/lower/upper) 1567 */ 1568 List<Type> filterBounds(UndetVar uv, InferenceContext inferenceContext) { 1569 return Type.filter(uv.getBounds(ib), new BoundFilter(inferenceContext)); 1570 } 1571 } 1572 1573 /** 1574 * This enumeration defines the sequence of steps to be applied when the 1575 * solver works in legacy mode. The steps in this enumeration reflect 1576 * the behavior of old inference routine (see JLS SE 7 15.12.2.7/15.12.2.8). 1577 */ 1578 enum LegacyInferenceSteps { 1579 1580 EQ_LOWER(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER)), 1581 EQ_UPPER(EnumSet.of(InferenceStep.EQ, InferenceStep.UPPER_LEGACY)); 1582 1583 final EnumSet<InferenceStep> steps; 1584 1585 LegacyInferenceSteps(EnumSet<InferenceStep> steps) { 1586 this.steps = steps; 1587 } 1588 } 1589 1590 /** 1591 * This enumeration defines the sequence of steps to be applied when the 1592 * graph solver is used. This order is defined so as to maximize compatibility 1593 * w.r.t. old inference routine (see JLS SE 7 15.12.2.7/15.12.2.8). 1594 */ 1595 enum GraphInferenceSteps { 1596 1597 EQ(EnumSet.of(InferenceStep.EQ)), 1598 EQ_LOWER(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER)), 1599 EQ_LOWER_THROWS_UPPER_CAPTURED(EnumSet.of(InferenceStep.EQ, InferenceStep.LOWER, InferenceStep.UPPER, InferenceStep.THROWS, InferenceStep.CAPTURED)); 1600 1601 final EnumSet<InferenceStep> steps; 1602 1603 GraphInferenceSteps(EnumSet<InferenceStep> steps) { 1604 this.steps = steps; 1605 } 1606 } 1607 1608 /** 1609 * There are two kinds of dependencies between inference variables. The basic 1610 * kind of dependency (or bound dependency) arises when a variable mention 1611 * another variable in one of its bounds. There's also a more subtle kind 1612 * of dependency that arises when a variable 'might' lead to better constraints 1613 * on another variable (this is typically the case with variables holding up 1614 * stuck expressions). 1615 */ 1616 enum DependencyKind implements GraphUtils.DependencyKind { 1617 1618 /** bound dependency */ 1619 BOUND("dotted"), 1620 /** stuck dependency */ 1621 STUCK("dashed"); 1622 1623 final String dotSyle; 1624 1625 private DependencyKind(String dotSyle) { 1626 this.dotSyle = dotSyle; 1627 } 1628 } 1629 1630 /** 1631 * This is the graph inference solver - the solver organizes all inference variables in 1632 * a given inference context by bound dependencies - in the general case, such dependencies 1633 * would lead to a cyclic directed graph (hence the name); the dependency info is used to build 1634 * an acyclic graph, where all cyclic variables are bundled together. An inference 1635 * step corresponds to solving a node in the acyclic graph - this is done by 1636 * relying on a given strategy (see GraphStrategy). 1637 */ 1638 class GraphSolver { 1639 1640 InferenceContext inferenceContext; 1641 Warner warn; 1642 1643 GraphSolver(InferenceContext inferenceContext, Warner warn) { 1644 this.inferenceContext = inferenceContext; 1645 this.warn = warn; 1646 } 1647 1648 /** 1649 * Solve variables in a given inference context. The amount of variables 1650 * to be solved, and the way in which the underlying acyclic graph is explored 1651 * depends on the selected solver strategy. 1652 */ 1653 void solve(GraphStrategy sstrategy) { 1654 doIncorporation(inferenceContext, warn); //initial propagation of bounds 1655 InferenceGraph inferenceGraph = new InferenceGraph(); 1656 while (!sstrategy.done()) { 1657 if (dependenciesFolder != null) { 1658 //add this graph to the pending queue 1659 pendingGraphs = pendingGraphs.prepend(inferenceGraph.toDot()); 1660 } 1661 InferenceGraph.Node nodeToSolve = sstrategy.pickNode(inferenceGraph); 1662 List<Type> varsToSolve = List.from(nodeToSolve.data); 1663 List<Type> saved_undet = inferenceContext.save(); 1664 try { 1665 //repeat until all variables are solved 1666 outer: while (Type.containsAny(inferenceContext.restvars(), varsToSolve)) { 1667 //for each inference phase 1668 for (GraphInferenceSteps step : GraphInferenceSteps.values()) { 1669 if (inferenceContext.solveBasic(varsToSolve, step.steps).nonEmpty()) { 1670 doIncorporation(inferenceContext, warn); 1671 continue outer; 1672 } 1673 } 1674 //no progress 1675 throw inferenceException.setMessage(); 1676 } 1677 } 1678 catch (InferenceException ex) { 1679 //did we fail because of interdependent ivars? 1680 inferenceContext.rollback(saved_undet); 1681 instantiateAsUninferredVars(varsToSolve, inferenceContext); 1682 doIncorporation(inferenceContext, warn); 1683 } 1684 inferenceGraph.deleteNode(nodeToSolve); 1685 } 1686 } 1687 1688 /** 1689 * The dependencies between the inference variables that need to be solved 1690 * form a (possibly cyclic) graph. This class reduces the original dependency graph 1691 * to an acyclic version, where cyclic nodes are folded into a single 'super node'. 1692 */ 1693 class InferenceGraph { 1694 1695 /** 1696 * This class represents a node in the graph. Each node corresponds 1697 * to an inference variable and has edges (dependencies) on other 1698 * nodes. The node defines an entry point that can be used to receive 1699 * updates on the structure of the graph this node belongs to (used to 1700 * keep dependencies in sync). 1701 */ 1702 class Node extends GraphUtils.TarjanNode<ListBuffer<Type>, Node> implements DottableNode<ListBuffer<Type>, Node> { 1703 1704 /** node dependencies */ 1705 Set<Node> deps; 1706 1707 Node(Type ivar) { 1708 super(ListBuffer.of(ivar)); 1709 this.deps = new HashSet<>(); 1710 } 1711 1712 @Override 1713 public GraphUtils.DependencyKind[] getSupportedDependencyKinds() { 1714 return new GraphUtils.DependencyKind[] { DependencyKind.BOUND }; 1715 } 1716 1717 public Iterable<? extends Node> getAllDependencies() { 1718 return deps; 1719 } 1720 1721 @Override 1722 public Collection<? extends Node> getDependenciesByKind(GraphUtils.DependencyKind dk) { 1723 if (dk == DependencyKind.BOUND) { 1724 return deps; 1725 } else { 1726 throw new IllegalStateException(); 1727 } 1728 } 1729 1730 /** 1731 * Adds dependency with given kind. 1732 */ 1733 protected void addDependency(Node depToAdd) { 1734 deps.add(depToAdd); 1735 } 1736 1737 /** 1738 * Add multiple dependencies of same given kind. 1739 */ 1740 protected void addDependencies(Set<Node> depsToAdd) { 1741 for (Node n : depsToAdd) { 1742 addDependency(n); 1743 } 1744 } 1745 1746 /** 1747 * Remove a dependency, regardless of its kind. 1748 */ 1749 protected boolean removeDependency(Node n) { 1750 return deps.remove(n); 1751 } 1752 1753 /** 1754 * Is this node a leaf? This means either the node has no dependencies, 1755 * or it just has self-dependencies. 1756 */ 1757 protected boolean isLeaf() { 1758 //no deps, or only one self dep 1759 if (deps.isEmpty()) return true; 1760 for (Node n : deps) { 1761 if (n != this) { 1762 return false; 1763 } 1764 } 1765 return true; 1766 } 1767 1768 /** 1769 * Merge this node with another node, acquiring its dependencies. 1770 * This routine is used to merge all cyclic node together and 1771 * form an acyclic graph. 1772 */ 1773 protected void mergeWith(List<? extends Node> nodes) { 1774 for (Node n : nodes) { 1775 Assert.check(n.data.length() == 1, "Attempt to merge a compound node!"); 1776 data.appendList(n.data); 1777 addDependencies(n.deps); 1778 } 1779 //update deps 1780 Set<Node> deps2 = new HashSet<>(); 1781 for (Node d : deps) { 1782 if (data.contains(d.data.first())) { 1783 deps2.add(this); 1784 } else { 1785 deps2.add(d); 1786 } 1787 } 1788 deps = deps2; 1789 } 1790 1791 /** 1792 * Notify all nodes that something has changed in the graph 1793 * topology. 1794 */ 1795 private void graphChanged(Node from, Node to) { 1796 if (removeDependency(from)) { 1797 if (to != null) { 1798 addDependency(to); 1799 } 1800 } 1801 } 1802 1803 @Override 1804 public Properties nodeAttributes() { 1805 Properties p = new Properties(); 1806 p.put("label", "\"" + toString() + "\""); 1807 return p; 1808 } 1809 1810 @Override 1811 public Properties dependencyAttributes(Node sink, GraphUtils.DependencyKind dk) { 1812 Properties p = new Properties(); 1813 p.put("style", ((DependencyKind)dk).dotSyle); 1814 StringBuilder buf = new StringBuilder(); 1815 String sep = ""; 1816 for (Type from : data) { 1817 UndetVar uv = (UndetVar)inferenceContext.asUndetVar(from); 1818 for (Type bound : uv.getBounds(InferenceBound.values())) { 1819 if (bound.containsAny(List.from(sink.data))) { 1820 buf.append(sep); 1821 buf.append(bound); 1822 sep = ","; 1823 } 1824 } 1825 } 1826 p.put("label", "\"" + buf.toString() + "\""); 1827 return p; 1828 } 1829 } 1830 1831 /** the nodes in the inference graph */ 1832 ArrayList<Node> nodes; 1833 1834 InferenceGraph() { 1835 initNodes(); 1836 } 1837 1838 /** 1839 * Basic lookup helper for retrieving a graph node given an inference 1840 * variable type. 1841 */ 1842 public Node findNode(Type t) { 1843 for (Node n : nodes) { 1844 if (n.data.contains(t)) { 1845 return n; 1846 } 1847 } 1848 return null; 1849 } 1850 1851 /** 1852 * Delete a node from the graph. This update the underlying structure 1853 * of the graph (including dependencies) via listeners updates. 1854 */ 1855 public void deleteNode(Node n) { 1856 Assert.check(nodes.contains(n)); 1857 nodes.remove(n); 1858 notifyUpdate(n, null); 1859 } 1860 1861 /** 1862 * Notify all nodes of a change in the graph. If the target node is 1863 * {@code null} the source node is assumed to be removed. 1864 */ 1865 void notifyUpdate(Node from, Node to) { 1866 for (Node n : nodes) { 1867 n.graphChanged(from, to); 1868 } 1869 } 1870 1871 /** 1872 * Create the graph nodes. First a simple node is created for every inference 1873 * variables to be solved. Then Tarjan is used to found all connected components 1874 * in the graph. For each component containing more than one node, a super node is 1875 * created, effectively replacing the original cyclic nodes. 1876 */ 1877 void initNodes() { 1878 //add nodes 1879 nodes = new ArrayList<>(); 1880 for (Type t : inferenceContext.restvars()) { 1881 nodes.add(new Node(t)); 1882 } 1883 //add dependencies 1884 for (Node n_i : nodes) { 1885 Type i = n_i.data.first(); 1886 for (Node n_j : nodes) { 1887 Type j = n_j.data.first(); 1888 UndetVar uv_i = (UndetVar)inferenceContext.asUndetVar(i); 1889 if (Type.containsAny(uv_i.getBounds(InferenceBound.values()), List.of(j))) { 1890 //update i's bound dependencies 1891 n_i.addDependency(n_j); 1892 } 1893 } 1894 } 1895 //merge cyclic nodes 1896 ArrayList<Node> acyclicNodes = new ArrayList<>(); 1897 for (List<? extends Node> conSubGraph : GraphUtils.tarjan(nodes)) { 1898 if (conSubGraph.length() > 1) { 1899 Node root = conSubGraph.head; 1900 root.mergeWith(conSubGraph.tail); 1901 for (Node n : conSubGraph) { 1902 notifyUpdate(n, root); 1903 } 1904 } 1905 acyclicNodes.add(conSubGraph.head); 1906 } 1907 nodes = acyclicNodes; 1908 } 1909 1910 /** 1911 * Debugging: dot representation of this graph 1912 */ 1913 String toDot() { 1914 StringBuilder buf = new StringBuilder(); 1915 for (Type t : inferenceContext.undetvars) { 1916 UndetVar uv = (UndetVar)t; 1917 buf.append(String.format("var %s - upper bounds = %s, lower bounds = %s, eq bounds = %s\\n", 1918 uv.qtype, uv.getBounds(InferenceBound.UPPER), uv.getBounds(InferenceBound.LOWER), 1919 uv.getBounds(InferenceBound.EQ))); 1920 } 1921 return GraphUtils.toDot(nodes, "inferenceGraph" + hashCode(), buf.toString()); 1922 } 1923 } 1924 } 1925 // </editor-fold> 1926 1927 // <editor-fold defaultstate="collapsed" desc="Inference context"> 1928 /** 1929 * Functional interface for defining inference callbacks. Certain actions 1930 * (i.e. subtyping checks) might need to be redone after all inference variables 1931 * have been fixed. 1932 */ 1933 interface FreeTypeListener { 1934 void typesInferred(InferenceContext inferenceContext); 1935 } 1936 1937 final InferenceContext emptyContext; 1938 // </editor-fold> 1939} 1940