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 /* -*- 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 "frontend/ParseMaps.h"

 #include "frontend/ParseNode.h"

 #include "frontend/TokenStream.h"

 #include "vm/ScopeObject.h"

 namespace js {

 namespace frontend {

 // 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. 'with' could be in

     // the non-example category, provided the set of all free variables within

     // the with block was noted. However, we do not optimize 'with' so, for

     // simplicity, 'with' is treated like eval.

     //

     // 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::argIsAlised).

     //

     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;

   public:

     AnyContextFlags()

      :  hasExplicitUseStrict(false),

         bindingsAccessedDynamically(false),

         hasDebuggerStatement(false)

     { }

 };

 class FunctionContextFlags

 {

     // This class's data is all private and so only visible to these friends.

     friend class FunctionBox;

     // The function or a function that encloses it may define new local names

     // at runtime through means other than calling eval.

     bool mightAliasLocals:1;

     // 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;

     // This function refers directly to its name in a way which requires the

     // name to be a separate object on the scope chain.

     bool needsDeclEnvObject: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;

   public:

     FunctionContextFlags()

      :  mightAliasLocals(false),

         hasExtensibleScope(false),

         needsDeclEnvObject(false),

         argumentsHasLocalBinding(false),

         definitelyNeedsArgsObj(false)

     { }

 };

 class GlobalSharedContext;

 // 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) {}

     template <typename ParseHandler> explicit Directives(ParseContext<ParseHandler> *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 struct SharedContext is part of the current parser context (see

  * ParseContext). It stores information that is reused between the parser and

  * the bytecode emitter. Note however, that this information is not shared

  * between the two; they simply reuse the same data structure.

  */

 class SharedContext

 {

   public:

     ExclusiveContext *const context;

     AnyContextFlags anyCxFlags;

     bool strict;

     bool extraWarnings;

     // If it's function code, funbox must be non-nullptr and scopeChain must be

     // nullptr. If it's global code, funbox must be nullptr.

     SharedContext(ExclusiveContext *cx, Directives directives, bool extraWarnings)

       : context(cx),

         anyCxFlags(),

         strict(directives.strict()),

         extraWarnings(extraWarnings)

     {}

     virtual ObjectBox *toObjectBox() = 0;

     inline bool isGlobalSharedContext() { return toObjectBox() == nullptr; }

     inline bool isFunctionBox() { return toObjectBox() && toObjectBox()->isFunctionBox(); }

     inline GlobalSharedContext *asGlobalSharedContext();

     inline FunctionBox *asFunctionBox();

     bool hasExplicitUseStrict()        const { return anyCxFlags.hasExplicitUseStrict; }

     bool bindingsAccessedDynamically() const { return anyCxFlags.bindingsAccessedDynamically; }

     bool hasDebuggerStatement()        const { return anyCxFlags.hasDebuggerStatement; }

     void setExplicitUseStrict()           { anyCxFlags.hasExplicitUseStrict        = true; }

     void setBindingsAccessedDynamically() { anyCxFlags.bindingsAccessedDynamically = true; }

     void setHasDebuggerStatement()        { anyCxFlags.hasDebuggerStatement        = true; }

     inline bool allLocalsAliased();

     // JSOPTION_EXTRA_WARNINGS warnings or strict mode errors.

     bool needStrictChecks() {

         return strict || extraWarnings;

     }

 };

 class GlobalSharedContext : public SharedContext

 {

   private:

     const RootedObject scopeChain_; /* scope chain object for the script */

   public:

     GlobalSharedContext(ExclusiveContext *cx, JSObject *scopeChain,

                         Directives directives, bool extraWarnings)

       : SharedContext(cx, directives, extraWarnings),

         scopeChain_(cx, scopeChain)

     {}

     ObjectBox *toObjectBox() { return nullptr; }

     JSObject *scopeChain() const { return scopeChain_; }

 };

 inline GlobalSharedContext *

 SharedContext::asGlobalSharedContext()

 {

     JS_ASSERT(isGlobalSharedContext());

     return static_cast<GlobalSharedContext*>(this);

 }

 class FunctionBox : public ObjectBox, public SharedContext

 {

   public:

     Bindings        bindings;               /* bindings for this function */

     uint32_t        bufStart;

     uint32_t        bufEnd;

     uint32_t        startLine;

     uint32_t        startColumn;

     uint16_t        length;

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

     bool            inWith:1;               /* some enclosing scope is a with-statement */

     bool            inGenexpLambda:1;       /* lambda from generator expression */

     bool            hasDestructuringArgs:1; /* arguments list contains destructuring expression */

     bool            useAsm:1;               /* function contains "use asm" directive */

     bool            insideUseAsm:1;         /* nested function of function of "use asm" directive */

     // Fields for use in heuristics.

     bool            usesArguments:1;  /* contains a free use of 'arguments' */

     bool            usesApply:1;      /* contains an f.apply() call */

     FunctionContextFlags funCxFlags;

     template <typename ParseHandler>

     FunctionBox(ExclusiveContext *cx, ObjectBox* traceListHead, JSFunction *fun,

                 ParseContext<ParseHandler> *pc, Directives directives,

                 bool extraWarnings, GeneratorKind generatorKind);

     ObjectBox *toObjectBox() { return this; }

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

     GeneratorKind generatorKind() const { return GeneratorKindFromBits(generatorKindBits_); }

     bool isGenerator() const { return generatorKind() != NotGenerator; }

     bool isLegacyGenerator() const { return generatorKind() == LegacyGenerator; }

     bool isStarGenerator() const { return generatorKind() == StarGenerator; }

     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.

         JS_ASSERT(!isGenerator());

         generatorKindBits_ = GeneratorKindAsBits(kind);

     }

     bool mightAliasLocals()         const { return funCxFlags.mightAliasLocals; }

     bool hasExtensibleScope()       const { return funCxFlags.hasExtensibleScope; }

     bool needsDeclEnvObject()       const { return funCxFlags.needsDeclEnvObject; }

     bool argumentsHasLocalBinding() const { return funCxFlags.argumentsHasLocalBinding; }

     bool definitelyNeedsArgsObj()   const { return funCxFlags.definitelyNeedsArgsObj; }

     void setMightAliasLocals()             { funCxFlags.mightAliasLocals         = true; }

     void setHasExtensibleScope()           { funCxFlags.hasExtensibleScope       = true; }

     void setNeedsDeclEnvObject()           { funCxFlags.needsDeclEnvObject       = true; }

     void setArgumentsHasLocalBinding()     { funCxFlags.argumentsHasLocalBinding = true; }

     void setDefinitelyNeedsArgsObj()       { JS_ASSERT(funCxFlags.argumentsHasLocalBinding);

                                              funCxFlags.definitelyNeedsArgsObj   = true; }

     bool hasDefaults() const {

         return length != function()->nargs() - function()->hasRest();

     }

     // Return whether this function has either specified "use asm" or is

     // (transitively) nested inside a function that has.

     bool useAsmOrInsideUseAsm() const {

         return useAsm || insideUseAsm;

     }

     void setStart(const TokenStream &tokenStream) {

         bufStart = tokenStream.currentToken().pos.begin;

         startLine = tokenStream.getLineno();

         startColumn = tokenStream.getColumn();

     }

     bool isHeavyweight()

     {

         // Note: this should be kept in sync with JSFunction::isHeavyweight().

         return bindings.hasAnyAliasedBindings() ||

                hasExtensibleScope() ||

                needsDeclEnvObject() ||

                isGenerator();

     }

 };

 inline FunctionBox *

 SharedContext::asFunctionBox()

 {

     JS_ASSERT(isFunctionBox());

     return static_cast<FunctionBox*>(this);

 }

 // In generators, we treat all locals as aliased 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::allLocalsAliased()

 {

     return bindingsAccessedDynamically() || (isFunctionBox() && asFunctionBox()->isGenerator());

 }

 /*

  * NB: If you add a new type of statement that is a scope, add it between

  * STMT_WITH and STMT_CATCH, or you will break StmtInfoBase::linksScope. If you

  * add a non-looping statement type, add it before STMT_DO_LOOP or you will

  * break StmtInfoBase::isLoop().

  *

  * Also remember to keep the statementName array in BytecodeEmitter.cpp in

  * sync.

  */

 enum StmtType {

     STMT_LABEL,                 /* labeled statement:  L: s */

     STMT_IF,                    /* if (then) statement */

     STMT_ELSE,                  /* else clause of if statement */

     STMT_SEQ,                   /* synthetic sequence of statements */

     STMT_BLOCK,                 /* compound statement: { s1[;... sN] } */

     STMT_SWITCH,                /* switch statement */

     STMT_WITH,                  /* with statement */

     STMT_CATCH,                 /* catch block */

     STMT_TRY,                   /* try block */

     STMT_FINALLY,               /* finally block */

     STMT_SUBROUTINE,            /* gosub-target subroutine body */

     STMT_DO_LOOP,               /* do/while loop statement */

     STMT_FOR_LOOP,              /* for loop statement */

     STMT_FOR_IN_LOOP,           /* for/in loop statement */

     STMT_FOR_OF_LOOP,           /* for/of loop statement */

     STMT_WHILE_LOOP,            /* while loop statement */

     STMT_LIMIT

 };

 /*

  * A comment on the encoding of the js::StmtType enum and StmtInfoBase

  * type-testing methods:

  *

  * StmtInfoBase::maybeScope() tells whether a statement type is always, or may

  * become, a lexical scope. It therefore includes block and switch (the two

  * low-numbered "maybe" scope types) and excludes with (with has dynamic scope

  * pending the "reformed with" in ES4/JS2). It includes all try-catch-finally

  * types, which are high-numbered maybe-scope types.

  *

  * StmtInfoBase::linksScope() tells whether a js::StmtInfo{PC,BCE} of the given

  * type eagerly links to other scoping statement info records. It excludes the

  * two early "maybe" types, block and switch, as well as the try and both

  * finally types, since try and the other trailing maybe-scope types don't need

  * block scope unless they contain let declarations.

  *

  * We treat WITH as a static scope because it prevents lexical binding from

  * continuing further up the static scope chain. With the lost "reformed with"

  * proposal for ES4, we would be able to model it statically, too.

  */

 // StmtInfoPC is used by the Parser.  StmtInfoBCE is used by the

 // BytecodeEmitter.  The two types have some overlap, encapsulated by

 // StmtInfoBase.  Several functions below (e.g. PushStatement) are templated to

 // work with both types.

 struct StmtInfoBase {

     // Statement type (StmtType).

     uint16_t        type;

     // True if type is STMT_BLOCK, STMT_TRY, STMT_SWITCH, or STMT_FINALLY and

     // the block contains at least one let-declaration, or if type is

     // STMT_CATCH.

     bool isBlockScope:1;

     // True if isBlockScope or type == STMT_WITH.

     bool isNestedScope:1;

     // for (let ...) induced block scope

     bool isForLetBlock:1;

     // Block label.

     RootedAtom      label;

     // Compile-time scope chain node for this scope.  Only set if

     // isNestedScope.

     Rooted<NestedScopeObject *> staticScope;

     StmtInfoBase(ExclusiveContext *cx)

         : isBlockScope(false), isNestedScope(false), isForLetBlock(false),

           label(cx), staticScope(cx)

     {}

     bool maybeScope() const {

         return STMT_BLOCK <= type && type <= STMT_SUBROUTINE && type != STMT_WITH;

     }

     bool linksScope() const {

         return isNestedScope;

     }

     StaticBlockObject& staticBlock() const {

         JS_ASSERT(isNestedScope);

         JS_ASSERT(isBlockScope);

         return staticScope->as<StaticBlockObject>();

     }

     bool isLoop() const {

         return type >= STMT_DO_LOOP;

     }

     bool isTrying() const {

         return STMT_TRY <= type && type <= STMT_SUBROUTINE;

     }

 };

 // Push the C-stack-allocated struct at stmt onto the StmtInfoPC stack.

 template <class ContextT>

 void

 PushStatement(ContextT *ct, typename ContextT::StmtInfo *stmt, StmtType type)

 {

     stmt->type = type;

     stmt->isBlockScope = false;

     stmt->isNestedScope = false;

     stmt->isForLetBlock = false;

     stmt->label = nullptr;

     stmt->staticScope = nullptr;

     stmt->down = ct->topStmt;

     ct->topStmt = stmt;

     if (stmt->linksScope()) {

         stmt->downScope = ct->topScopeStmt;

         ct->topScopeStmt = stmt;

     } else {

         stmt->downScope = nullptr;

     }

 }

 template <class ContextT>

 void

 FinishPushNestedScope(ContextT *ct, typename ContextT::StmtInfo *stmt, NestedScopeObject &staticScope)

 {

     stmt->isNestedScope = true;

     stmt->downScope = ct->topScopeStmt;

     ct->topScopeStmt = stmt;

     ct->staticScope = &staticScope;

     stmt->staticScope = &staticScope;

 }

 // Pop pc->topStmt. If the top StmtInfoPC struct is not stack-allocated, it

 // is up to the caller to free it.  The dummy argument is just to make the

 // template matching work.

 template <class ContextT>

 void

 FinishPopStatement(ContextT *ct)

 {

     typename ContextT::StmtInfo *stmt = ct->topStmt;

     ct->topStmt = stmt->down;

     if (stmt->linksScope()) {

         ct->topScopeStmt = stmt->downScope;

         if (stmt->isNestedScope) {

             JS_ASSERT(stmt->staticScope);

             ct->staticScope = stmt->staticScope->enclosingNestedScope();

         }

     }

 }

 /*

  * Find a lexically scoped variable (one declared by let, catch, or an array

  * comprehension) named by atom, looking in sc's compile-time scopes.

  *

  * If a WITH statement is reached along the scope stack, return its statement

  * info record, so callers can tell that atom is ambiguous. If slotp is not

  * null, then if atom is found, set *slotp to its stack slot, otherwise to -1.

  * This means that if slotp is not null, all the block objects on the lexical

  * scope chain must have had their depth slots computed by the code generator,

  * so the caller must be under EmitTree.

  *

  * In any event, directly return the statement info record in which atom was

  * found. Otherwise return null.

  */

 template <class ContextT>

 typename ContextT::StmtInfo *

 LexicalLookup(ContextT *ct, HandleAtom atom, int *slotp, typename ContextT::StmtInfo *stmt);

 } // namespace frontend

 } // namespace js

 #endif /* frontend_SharedContext_h */