summaryrefslogtreecommitdiffstats
path: root/js/src/frontend/SharedContext.h
blob: 2d478308ec6276a4f16c7222667b37c53ad3ef15 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef frontend_SharedContext_h
#define frontend_SharedContext_h

#include "jsatom.h"
#include "jsopcode.h"
#include "jspubtd.h"
#include "jsscript.h"
#include "jstypes.h"

#include "builtin/ModuleObject.h"
#include "ds/InlineTable.h"
#include "frontend/ParseNode.h"
#include "frontend/TokenStream.h"
#include "vm/EnvironmentObject.h"

namespace js {
namespace frontend {

enum class StatementKind : uint8_t
{
    Label,
    Block,
    If,
    Switch,
    With,
    Catch,
    Try,
    Finally,
    ForLoopLexicalHead,
    ForLoop,
    ForInLoop,
    ForOfLoop,
    DoLoop,
    WhileLoop,
    Class,

    // Used only by BytecodeEmitter.
    Spread
};

static inline bool
StatementKindIsLoop(StatementKind kind)
{
    return kind == StatementKind::ForLoop ||
           kind == StatementKind::ForInLoop ||
           kind == StatementKind::ForOfLoop ||
           kind == StatementKind::DoLoop ||
           kind == StatementKind::WhileLoop ||
           kind == StatementKind::Spread;
}

static inline bool
StatementKindIsUnlabeledBreakTarget(StatementKind kind)
{
    return StatementKindIsLoop(kind) || kind == StatementKind::Switch;
}

// A base class for nestable structures in the frontend, such as statements
// and scopes.
template <typename Concrete>
class MOZ_STACK_CLASS Nestable
{
    Concrete** stack_;
    Concrete*  enclosing_;

  protected:
    explicit Nestable(Concrete** stack)
      : stack_(stack),
        enclosing_(*stack)
    {
        *stack_ = static_cast<Concrete*>(this);
    }

    // These method are protected. Some derived classes, such as ParseContext,
    // do not expose the ability to walk the stack.
    Concrete* enclosing() const {
        return enclosing_;
    }

    template <typename Predicate /* (Concrete*) -> bool */>
    static Concrete* findNearest(Concrete* it, Predicate predicate) {
        while (it && !predicate(it))
            it = it->enclosing();
        return it;
    }

    template <typename T>
    static T* findNearest(Concrete* it) {
        while (it && !it->template is<T>())
            it = it->enclosing();
        return it ? &it->template as<T>() : nullptr;
    }

    template <typename T, typename Predicate /* (T*) -> bool */>
    static T* findNearest(Concrete* it, Predicate predicate) {
        while (it && (!it->template is<T>() || !predicate(&it->template as<T>())))
            it = it->enclosing();
        return it ? &it->template as<T>() : nullptr;
    }

  public:
    ~Nestable() {
        MOZ_ASSERT(*stack_ == static_cast<Concrete*>(this));
        *stack_ = enclosing_;
    }
};

// These flags apply to both global and function contexts.
class AnyContextFlags
{
    // This class's data is all private and so only visible to these friends.
    friend class SharedContext;

    // True if "use strict"; appears in the body instead of being inherited.
    bool hasExplicitUseStrict:1;

    // The (static) bindings of this script need to support dynamic name
    // read/write access. Here, 'dynamic' means dynamic dictionary lookup on
    // the scope chain for a dynamic set of keys. The primary examples are:
    //  - direct eval
    //  - function::
    //  - with
    // since both effectively allow any name to be accessed. Non-examples are:
    //  - upvars of nested functions
    //  - function statement
    // since the set of assigned name is known dynamically.
    //
    // Note: access through the arguments object is not considered dynamic
    // binding access since it does not go through the normal name lookup
    // mechanism. This is debatable and could be changed (although care must be
    // taken not to turn off the whole 'arguments' optimization). To answer the
    // more general "is this argument aliased" question, script->needsArgsObj
    // should be tested (see JSScript::argIsAliased).
    bool bindingsAccessedDynamically:1;

    // Whether this script, or any of its inner scripts contains a debugger
    // statement which could potentially read or write anywhere along the
    // scope chain.
    bool hasDebuggerStatement:1;

    // A direct eval occurs in the body of the script.
    bool hasDirectEval:1;

  public:
    AnyContextFlags()
     :  hasExplicitUseStrict(false),
        bindingsAccessedDynamically(false),
        hasDebuggerStatement(false),
        hasDirectEval(false)
    { }
};

class FunctionContextFlags
{
    // This class's data is all private and so only visible to these friends.
    friend class FunctionBox;

    // This function does something that can extend the set of bindings in its
    // call objects --- it does a direct eval in non-strict code, or includes a
    // function statement (as opposed to a function definition).
    //
    // This flag is *not* inherited by enclosed or enclosing functions; it
    // applies only to the function in whose flags it appears.
    //
    bool hasExtensibleScope:1;

    // Technically, every function has a binding named 'arguments'. Internally,
    // this binding is only added when 'arguments' is mentioned by the function
    // body. This flag indicates whether 'arguments' has been bound either
    // through implicit use:
    //   function f() { return arguments }
    // or explicit redeclaration:
    //   function f() { var arguments; return arguments }
    //
    // Note 1: overwritten arguments (function() { arguments = 3 }) will cause
    // this flag to be set but otherwise require no special handling:
    // 'arguments' is just a local variable and uses of 'arguments' will just
    // read the local's current slot which may have been assigned. The only
    // special semantics is that the initial value of 'arguments' is the
    // arguments object (not undefined, like normal locals).
    //
    // Note 2: if 'arguments' is bound as a formal parameter, there will be an
    // 'arguments' in Bindings, but, as the "LOCAL" in the name indicates, this
    // flag will not be set. This is because, as a formal, 'arguments' will
    // have no special semantics: the initial value is unconditionally the
    // actual argument (or undefined if nactual < nformal).
    //
    bool argumentsHasLocalBinding:1;

    // In many cases where 'arguments' has a local binding (as described above)
    // we do not need to actually create an arguments object in the function
    // prologue: instead we can analyze how 'arguments' is used (using the
    // simple dataflow analysis in analyzeSSA) to determine that uses of
    // 'arguments' can just read from the stack frame directly. However, the
    // dataflow analysis only looks at how JSOP_ARGUMENTS is used, so it will
    // be unsound in several cases. The frontend filters out such cases by
    // setting this flag which eagerly sets script->needsArgsObj to true.
    //
    bool definitelyNeedsArgsObj:1;

    bool needsHomeObject:1;
    bool isDerivedClassConstructor:1;

    // Whether this function has a .this binding. If true, we need to emit
    // JSOP_FUNCTIONTHIS in the prologue to initialize it.
    bool hasThisBinding:1;

    // Whether this function has nested functions.
    bool hasInnerFunctions:1;

  public:
    FunctionContextFlags()
     :  hasExtensibleScope(false),
        argumentsHasLocalBinding(false),
        definitelyNeedsArgsObj(false),
        needsHomeObject(false),
        isDerivedClassConstructor(false),
        hasThisBinding(false),
        hasInnerFunctions(false)
    { }
};

// List of directives that may be encountered in a Directive Prologue (ES5 15.1).
class Directives
{
    bool strict_;
    bool asmJS_;

  public:
    explicit Directives(bool strict) : strict_(strict), asmJS_(false) {}
    explicit Directives(ParseContext* parent);

    void setStrict() { strict_ = true; }
    bool strict() const { return strict_; }

    void setAsmJS() { asmJS_ = true; }
    bool asmJS() const { return asmJS_; }

    Directives& operator=(Directives rhs) {
        strict_ = rhs.strict_;
        asmJS_ = rhs.asmJS_;
        return *this;
    }
    bool operator==(const Directives& rhs) const {
        return strict_ == rhs.strict_ && asmJS_ == rhs.asmJS_;
    }
    bool operator!=(const Directives& rhs) const {
        return !(*this == rhs);
    }
};

// The kind of this-binding for the current scope. Note that arrow functions
// (and generator expression lambdas) have a lexical this-binding so their
// ThisBinding is the same as the ThisBinding of their enclosing scope and can
// be any value.
enum class ThisBinding { Global, Function, Module };

class GlobalSharedContext;
class EvalSharedContext;
class ModuleSharedContext;

/*
 * The struct SharedContext is part of the current parser context (see
 * ParseContext). It stores information that is reused between the parser and
 * the bytecode emitter.
 */
class SharedContext
{
  public:
    ExclusiveContext* const context;
    AnyContextFlags anyCxFlags;
    bool strictScript;
    bool localStrict;
    bool extraWarnings;

  protected:
    enum class Kind {
        ObjectBox,
        Global,
        Eval,
        Module
    };

    Kind kind_;

    ThisBinding thisBinding_;

    bool allowNewTarget_;
    bool allowSuperProperty_;
    bool allowSuperCall_;
    bool inWith_;
    bool needsThisTDZChecks_;

    void computeAllowSyntax(Scope* scope);
    void computeInWith(Scope* scope);
    void computeThisBinding(Scope* scope);

  public:
    SharedContext(ExclusiveContext* cx, Kind kind, Directives directives, bool extraWarnings)
      : context(cx),
        anyCxFlags(),
        strictScript(directives.strict()),
        localStrict(false),
        extraWarnings(extraWarnings),
        kind_(kind),
        thisBinding_(ThisBinding::Global),
        allowNewTarget_(false),
        allowSuperProperty_(false),
        allowSuperCall_(false),
        inWith_(false),
        needsThisTDZChecks_(false)
    { }

    // If this is the outermost SharedContext, the Scope that encloses
    // it. Otherwise nullptr.
    virtual Scope* compilationEnclosingScope() const = 0;

    virtual ObjectBox* toObjectBox() { return nullptr; }
    bool isObjectBox() { return toObjectBox(); }
    bool isFunctionBox() { return isObjectBox() && toObjectBox()->isFunctionBox(); }
    inline FunctionBox* asFunctionBox();
    bool isModuleContext() { return kind_ == Kind::Module; }
    inline ModuleSharedContext* asModuleContext();
    bool isGlobalContext() { return kind_ == Kind::Global; }
    inline GlobalSharedContext* asGlobalContext();
    bool isEvalContext() { return kind_ == Kind::Eval; }
    inline EvalSharedContext* asEvalContext();

    ThisBinding thisBinding()          const { return thisBinding_; }

    bool allowNewTarget()              const { return allowNewTarget_; }
    bool allowSuperProperty()          const { return allowSuperProperty_; }
    bool allowSuperCall()              const { return allowSuperCall_; }
    bool inWith()                      const { return inWith_; }
    bool needsThisTDZChecks()          const { return needsThisTDZChecks_; }

    bool hasExplicitUseStrict()        const { return anyCxFlags.hasExplicitUseStrict; }
    bool bindingsAccessedDynamically() const { return anyCxFlags.bindingsAccessedDynamically; }
    bool hasDebuggerStatement()        const { return anyCxFlags.hasDebuggerStatement; }
    bool hasDirectEval()               const { return anyCxFlags.hasDirectEval; }

    void setExplicitUseStrict()           { anyCxFlags.hasExplicitUseStrict        = true; }
    void setBindingsAccessedDynamically() { anyCxFlags.bindingsAccessedDynamically = true; }
    void setHasDebuggerStatement()        { anyCxFlags.hasDebuggerStatement        = true; }
    void setHasDirectEval()               { anyCxFlags.hasDirectEval               = true; }

    inline bool allBindingsClosedOver();

    bool strict() const {
        return strictScript || localStrict;
    }
    bool setLocalStrictMode(bool strict) {
        bool retVal = localStrict;
        localStrict = strict;
        return retVal;
    }

    // JSOPTION_EXTRA_WARNINGS warnings or strict mode errors.
    bool needStrictChecks() const {
        return strict() || extraWarnings;
    }

    bool isDotVariable(JSAtom* atom) const {
        return atom == context->names().dotGenerator || atom == context->names().dotThis;
    }
};

class MOZ_STACK_CLASS GlobalSharedContext : public SharedContext
{
    ScopeKind scopeKind_;

  public:
    Rooted<GlobalScope::Data*> bindings;

    GlobalSharedContext(ExclusiveContext* cx, ScopeKind scopeKind, Directives directives,
                        bool extraWarnings)
      : SharedContext(cx, Kind::Global, directives, extraWarnings),
        scopeKind_(scopeKind),
        bindings(cx)
    {
        MOZ_ASSERT(scopeKind == ScopeKind::Global || scopeKind == ScopeKind::NonSyntactic);
        thisBinding_ = ThisBinding::Global;
    }

    Scope* compilationEnclosingScope() const override {
        return nullptr;
    }

    ScopeKind scopeKind() const {
        return scopeKind_;
    }
};

inline GlobalSharedContext*
SharedContext::asGlobalContext()
{
    MOZ_ASSERT(isGlobalContext());
    return static_cast<GlobalSharedContext*>(this);
}

class MOZ_STACK_CLASS EvalSharedContext : public SharedContext
{
    RootedScope enclosingScope_;

  public:
    Rooted<EvalScope::Data*> bindings;

    EvalSharedContext(ExclusiveContext* cx, JSObject* enclosingEnv, Scope* enclosingScope,
                      Directives directives, bool extraWarnings);

    Scope* compilationEnclosingScope() const override {
        return enclosingScope_;
    }
};

inline EvalSharedContext*
SharedContext::asEvalContext()
{
    MOZ_ASSERT(isEvalContext());
    return static_cast<EvalSharedContext*>(this);
}

class FunctionBox : public ObjectBox, public SharedContext
{
    // The parser handles tracing the fields below via the ObjectBox linked
    // list.

    Scope* enclosingScope_;

    // Names from the named lambda scope, if a named lambda.
    LexicalScope::Data* namedLambdaBindings_;

    // Names from the function scope.
    FunctionScope::Data* functionScopeBindings_;

    // Names from the extra 'var' scope of the function, if the parameter list
    // has expressions.
    VarScope::Data* extraVarScopeBindings_;

    void initWithEnclosingScope(Scope* enclosingScope);

  public:
    ParseNode*      functionNode;           /* back pointer used by asm.js for error messages */
    uint32_t        bufStart;
    uint32_t        bufEnd;
    uint32_t        startLine;
    uint32_t        startColumn;
    uint32_t        toStringStart;
    uint32_t        toStringEnd;
    uint16_t        length;

    uint8_t         generatorKindBits_;     /* The GeneratorKind of this function. */
    uint8_t         asyncKindBits_;         /* The FunctionAsyncKing of this function. */

    bool            isGenexpLambda:1;       /* lambda from generator expression */
    bool            hasDestructuringArgs:1; /* parameter list contains destructuring expression */
    bool            hasParameterExprs:1;    /* parameter list contains expressions */
    bool            hasDirectEvalInParameterExpr:1; /* parameter list contains direct eval */
    bool            hasDuplicateParameters:1; /* parameter list contains duplicate names */
    bool            useAsm:1;               /* see useAsmOrInsideUseAsm */
    bool            insideUseAsm:1;         /* see useAsmOrInsideUseAsm */
    bool            isAnnexB:1;             /* need to emit a synthesized Annex B assignment */
    bool            wasEmitted:1;           /* Bytecode has been emitted for this function. */

    // Fields for use in heuristics.
    bool            declaredArguments:1;    /* the Parser declared 'arguments' */
    bool            usesArguments:1;        /* contains a free use of 'arguments' */
    bool            usesApply:1;            /* contains an f.apply() call */
    bool            usesThis:1;             /* contains 'this' */
    bool            usesReturn:1;           /* contains a 'return' statement */
    bool            hasRest_:1;             /* has rest parameter */
    bool            isExprBody_:1;          /* arrow function with expression
                                             * body or expression closure:
                                             * function(x) x*x */

    FunctionContextFlags funCxFlags;

    FunctionBox(ExclusiveContext* cx, LifoAlloc& alloc, ObjectBox* traceListHead, JSFunction* fun,
                uint32_t toStringStart, Directives directives, bool extraWarnings,
                GeneratorKind generatorKind, FunctionAsyncKind asyncKind);

    MutableHandle<LexicalScope::Data*> namedLambdaBindings() {
        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
        return MutableHandle<LexicalScope::Data*>::fromMarkedLocation(&namedLambdaBindings_);
    }

    MutableHandle<FunctionScope::Data*> functionScopeBindings() {
        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
        return MutableHandle<FunctionScope::Data*>::fromMarkedLocation(&functionScopeBindings_);
    }

    MutableHandle<VarScope::Data*> extraVarScopeBindings() {
        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
        return MutableHandle<VarScope::Data*>::fromMarkedLocation(&extraVarScopeBindings_);
    }

    void initFromLazyFunction();
    void initStandaloneFunction(Scope* enclosingScope);
    void initWithEnclosingParseContext(ParseContext* enclosing, FunctionSyntaxKind kind);

    ObjectBox* toObjectBox() override { return this; }
    JSFunction* function() const { return &object->as<JSFunction>(); }

    Scope* compilationEnclosingScope() const override {
        // This method is used to distinguish the outermost SharedContext. If
        // a FunctionBox is the outermost SharedContext, it must be a lazy
        // function.
        MOZ_ASSERT_IF(function()->isInterpretedLazy(),
                      enclosingScope_ == function()->lazyScript()->enclosingScope());
        return enclosingScope_;
    }

    bool needsCallObjectRegardlessOfBindings() const {
        return hasExtensibleScope() ||
               needsHomeObject() ||
               isDerivedClassConstructor() ||
               isStarGenerator() ||
               isLegacyGenerator() ||
               isAsync();
    }

    bool hasExtraBodyVarScope() const {
        return hasParameterExprs &&
               (extraVarScopeBindings_ ||
                needsExtraBodyVarEnvironmentRegardlessOfBindings());
    }

    bool needsExtraBodyVarEnvironmentRegardlessOfBindings() const {
        MOZ_ASSERT(hasParameterExprs);
        return hasExtensibleScope() || needsDotGeneratorName();
    }

    bool isLikelyConstructorWrapper() const {
        return usesArguments && usesApply && usesThis && !usesReturn;
    }

    GeneratorKind generatorKind() const { return GeneratorKindFromBits(generatorKindBits_); }
    bool isLegacyGenerator() const { return generatorKind() == LegacyGenerator; }
    bool isStarGenerator() const { return generatorKind() == StarGenerator; }
    FunctionAsyncKind asyncKind() const { return AsyncKindFromBits(asyncKindBits_); }

    bool needsFinalYield() const {
        return isStarGenerator() || isLegacyGenerator() || isAsync();
    }
    bool needsDotGeneratorName() const {
        return isStarGenerator() || isLegacyGenerator() || isAsync();
    }

    bool needsIteratorResult() const {
        return isStarGenerator() || isAsync();
    }

    bool isAsync() const { return asyncKind() == AsyncFunction; }
    bool isArrow() const { return function()->isArrow(); }

    bool hasRest() const { return hasRest_; }
    void setHasRest() {
        hasRest_ = true;
    }

    bool isExprBody() const { return isExprBody_; }
    void setIsExprBody() {
        isExprBody_ = true;
    }

    void setGeneratorKind(GeneratorKind kind) {
        // A generator kind can be set at initialization, or when "yield" is
        // first seen.  In both cases the transition can only happen from
        // NotGenerator.
        MOZ_ASSERT(!isStarGenerator() && !isLegacyGenerator());
        generatorKindBits_ = GeneratorKindAsBits(kind);
    }

    bool hasExtensibleScope()        const { return funCxFlags.hasExtensibleScope; }
    bool hasThisBinding()            const { return funCxFlags.hasThisBinding; }
    bool argumentsHasLocalBinding()  const { return funCxFlags.argumentsHasLocalBinding; }
    bool definitelyNeedsArgsObj()    const { return funCxFlags.definitelyNeedsArgsObj; }
    bool needsHomeObject()           const { return funCxFlags.needsHomeObject; }
    bool isDerivedClassConstructor() const { return funCxFlags.isDerivedClassConstructor; }
    bool hasInnerFunctions()         const { return funCxFlags.hasInnerFunctions; }

    void setHasExtensibleScope()           { funCxFlags.hasExtensibleScope       = true; }
    void setHasThisBinding()               { funCxFlags.hasThisBinding           = true; }
    void setArgumentsHasLocalBinding()     { funCxFlags.argumentsHasLocalBinding = true; }
    void setDefinitelyNeedsArgsObj()       { MOZ_ASSERT(funCxFlags.argumentsHasLocalBinding);
                                             funCxFlags.definitelyNeedsArgsObj   = true; }
    void setNeedsHomeObject()              { MOZ_ASSERT(function()->allowSuperProperty());
                                             funCxFlags.needsHomeObject          = true; }
    void setDerivedClassConstructor()      { MOZ_ASSERT(function()->isClassConstructor());
                                             funCxFlags.isDerivedClassConstructor = true; }
    void setHasInnerFunctions()            { funCxFlags.hasInnerFunctions         = true; }

    bool hasSimpleParameterList() const {
        return !hasRest() && !hasParameterExprs && !hasDestructuringArgs;
    }

    bool hasMappedArgsObj() const {
        return !strict() && hasSimpleParameterList();
    }

    // Return whether this or an enclosing function is being parsed and
    // validated as asm.js. Note: if asm.js validation fails, this will be false
    // while the function is being reparsed. This flag can be used to disable
    // certain parsing features that are necessary in general, but unnecessary
    // for validated asm.js.
    bool useAsmOrInsideUseAsm() const {
        return useAsm || insideUseAsm;
    }

    void setStart(const TokenStream& tokenStream) {
        bufStart = tokenStream.currentToken().pos.begin;
        tokenStream.srcCoords.lineNumAndColumnIndex(bufStart, &startLine, &startColumn);
    }

    void setEnd(uint32_t end) {
        // For all functions except class constructors, the buffer and
        // toString ending positions are the same. Class constructors override
        // the toString ending position with the end of the class definition.
        bufEnd = end;
        toStringEnd = end;
    }

    void trace(JSTracer* trc) override;
};

inline FunctionBox*
SharedContext::asFunctionBox()
{
    MOZ_ASSERT(isFunctionBox());
    return static_cast<FunctionBox*>(this);
}

class MOZ_STACK_CLASS ModuleSharedContext : public SharedContext
{
    RootedModuleObject module_;
    RootedScope enclosingScope_;

  public:
    Rooted<ModuleScope::Data*> bindings;
    ModuleBuilder& builder;

    ModuleSharedContext(ExclusiveContext* cx, ModuleObject* module, Scope* enclosingScope,
                        ModuleBuilder& builder);

    HandleModuleObject module() const { return module_; }
    Scope* compilationEnclosingScope() const override { return enclosingScope_; }
};

inline ModuleSharedContext*
SharedContext::asModuleContext()
{
    MOZ_ASSERT(isModuleContext());
    return static_cast<ModuleSharedContext*>(this);
}

// In generators, we treat all bindings as closed so that they get stored on
// the heap.  This way there is less information to copy off the stack when
// suspending, and back on when resuming.  It also avoids the need to create
// and invalidate DebugScope proxies for unaliased locals in a generator
// frame, as the generator frame will be copied out to the heap and released
// only by GC.
inline bool
SharedContext::allBindingsClosedOver()
{
    return bindingsAccessedDynamically() ||
           (isFunctionBox() &&
            (asFunctionBox()->isStarGenerator() ||
             asFunctionBox()->isLegacyGenerator() ||
             asFunctionBox()->isAsync()));
}

} // namespace frontend
} // namespace js

#endif /* frontend_SharedContext_h */