[es6] implement destructuring assignment

src/pattern-rewriter.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast.h"
 #include "src/messages.h"
 #include "src/parameter-initializer-rewriter.h"
 #include "src/parser.h"
 
 namespace v8 {
 
 namespace internal {
 
 
 void Parser::PatternRewriter::DeclareAndInitializeVariables(
     Block* block, const DeclarationDescriptor* declaration_descriptor,
     const DeclarationParsingResult::Declaration* declaration,
     ZoneList<const AstRawString*>* names, bool* ok) {
   PatternRewriter rewriter;
 
+  rewriter.scope_ = declaration_descriptor->scope;
+  rewriter.parser_ = declaration_descriptor->parser;
+  rewriter.context_ = BINDING;
   rewriter.pattern_ = declaration->pattern;
   rewriter.initializer_position_ = declaration->initializer_position;
   rewriter.block_ = block;
   rewriter.descriptor_ = declaration_descriptor;
   rewriter.names_ = names;
   rewriter.ok_ = ok;
 
   rewriter.RecurseIntoSubpattern(rewriter.pattern_, declaration->initializer);
 }
 
 
+void Parser::PatternRewriter::RewriteDestructuringAssignment(
+    Parser* parser, Assignment* assignment, Scope* scope, bool* ok) {
+  PatternRewriter rewriter;
+
+  DCHECK(assignment->is_destructuring_assignment());
+  DCHECK_EQ(assignment->op(), Token::ASSIGN);
+
+  rewriter.scope_ = scope;
+  rewriter.parser_ = parser;
+  rewriter.context_ = ASSIGNMENT;
+  rewriter.pattern_ = assignment;
+  rewriter.block_ = nullptr;
+  rewriter.descriptor_ = nullptr;
+  rewriter.names_ = nullptr;
+  rewriter.ok_ = ok;
+
+  rewriter.RecurseIntoSubpattern(rewriter.pattern_, nullptr);
+}
+
+
 void Parser::PatternRewriter::VisitVariableProxy(VariableProxy* pattern) {
   Expression* value = current_value_;
+
+  if (IsAssignmentContext()) {
+    // In an assignment context, simply perform the assignment
+    Assignment* assignment = factory()->NewAssignment(
+        Token::ASSIGN, pattern, value, pattern->position());
+    block_->statements()->Add(
+        factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+        zone());
+    return;
+  }
+
   descriptor_->scope->RemoveUnresolved(pattern);
 
   // Declare variable.
   // Note that we *always* must treat the initial value via a separate init
   // assignment for variables and constants because the value must be assigned
   // when the variable is encountered in the source. But the variable/constant
   // is declared (and set to 'undefined') upon entering the function within
   // which the variable or constant is declared. Only function variables have
   // an initial value in the declaration (because they are initialized upon
   // entering the function).
   //
   // If we have a legacy const declaration, in an inner scope, the proxy
   // is always bound to the declared variable (independent of possibly
   // surrounding 'with' statements).
   // For let/const declarations in harmony mode, we can also immediately
   // pre-resolve the proxy because it resides in the same scope as the
   // declaration.
-  Parser* parser = descriptor_->parser;
   const AstRawString* name = pattern->raw_name();
-  VariableProxy* proxy = parser->NewUnresolved(name, descriptor_->mode);
+  VariableProxy* proxy = parser_->NewUnresolved(name, descriptor_->mode);
   Declaration* declaration = factory()->NewVariableDeclaration(
       proxy, descriptor_->mode, descriptor_->scope,
       descriptor_->declaration_pos);
-  Variable* var = parser->Declare(declaration, descriptor_->declaration_kind,
-                                  descriptor_->mode != VAR, ok_,
-                                  descriptor_->hoist_scope);
+  Variable* var =
+      parser_->Declare(declaration, descriptor_->declaration_kind,
+                       descriptor_->mode != VAR, ok_, descriptor_->hoist_scope);
   if (!*ok_) return;
   DCHECK_NOT_NULL(var);
   DCHECK(!proxy->is_resolved() || proxy->var() == var);
   var->set_initializer_position(initializer_position_);
 
   DCHECK(initializer_position_ != RelocInfo::kNoPosition);
 
   if (descriptor_->declaration_scope->num_var_or_const() >
       kMaxNumFunctionLocals) {
-    parser->ReportMessage(MessageTemplate::kTooManyVariables);
+    parser_->ReportMessage(MessageTemplate::kTooManyVariables);
     *ok_ = false;
     return;
   }
   if (names_) {
     names_->Add(name, zone());
   }
 
   // Initialize variables if needed. A
   // declaration of the form:
   //
@@ skipping 127 matching lines @@
     Assignment* assignment = factory()->NewAssignment(
         Token::INIT, proxy, value, descriptor_->initialization_pos);
     block_->statements()->Add(
         factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
         zone());
   }
 }
 
 
 Variable* Parser::PatternRewriter::CreateTempVar(Expression* value) {
-  auto temp = descriptor_->parser->scope_->NewTemporary(
-      ast_value_factory()->empty_string());
+  auto temp = scope()->NewTemporary(ast_value_factory()->empty_string());
   if (value != nullptr) {
     auto assignment = factory()->NewAssignment(
         Token::ASSIGN, factory()->NewVariableProxy(temp), value,
         RelocInfo::kNoPosition);
 
     block_->statements()->Add(
         factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
         zone());
   }
   return temp;
 }
 
 
-void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern) {
-  auto temp = CreateTempVar(current_value_);
+void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern,
+                                                 Variable** temp_var) {
+  auto temp = *temp_var = CreateTempVar(current_value_);
 
-  block_->statements()->Add(descriptor_->parser->BuildAssertIsCoercible(temp),
-                            zone());
+  block_->statements()->Add(parser_->BuildAssertIsCoercible(temp), zone());
 
   for (ObjectLiteralProperty* property : *pattern->properties()) {
+    PatternContext context = SetInitializerContextIfNeeded(property->value());
     RecurseIntoSubpattern(
         property->value(),
         factory()->NewProperty(factory()->NewVariableProxy(temp),
                                property->key(), RelocInfo::kNoPosition));
+    set_context(context);

[adamk, 2015/11/25 21:05:28]

Can you use an RAII object for this instead of relying on set_context at the end
of the block to handle this?

[caitp (gmail), 2015/11/25 21:41:51]

Doable, but it is (relatively) a lot of code and I don't think it needs to be
used a whole lot. I'll put that in the next patch

[adamk, 2015/11/25 21:54:20]

I'm ok with this for now if you feel like there just aren't enough callers to be
worth it.

   }
 }
 
 
-void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node) {
-  auto temp = CreateTempVar(current_value_);
+void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node,
+                                                Variable** temp_var) {
+  auto temp = *temp_var = CreateTempVar(current_value_);
 
-  block_->statements()->Add(descriptor_->parser->BuildAssertIsCoercible(temp),
-                            zone());
+  block_->statements()->Add(parser_->BuildAssertIsCoercible(temp), zone());
 
-  auto iterator = CreateTempVar(descriptor_->parser->GetIterator(
-      factory()->NewVariableProxy(temp), factory()));
+  auto iterator = CreateTempVar(
+      parser_->GetIterator(factory()->NewVariableProxy(temp), factory()));
   auto done = CreateTempVar(
       factory()->NewBooleanLiteral(false, RelocInfo::kNoPosition));
   auto result = CreateTempVar();
   auto v = CreateTempVar();
 
   Spread* spread = nullptr;
   for (Expression* value : *node->values()) {
     if (value->IsSpread()) {
       spread = value->AsSpread();
       break;
     }
 
+    PatternContext context = SetInitializerContextIfNeeded(value);
     // if (!done) {
     //   result = IteratorNext(iterator);
     //   v = (done = result.done) ? undefined : result.value;
     // }
     auto next_block =
         factory()->NewBlock(nullptr, 2, true, RelocInfo::kNoPosition);
-    next_block->statements()->Add(
-        factory()->NewExpressionStatement(
-            descriptor_->parser->BuildIteratorNextResult(
-                factory()->NewVariableProxy(iterator), result,
-                RelocInfo::kNoPosition),
-            RelocInfo::kNoPosition),
-        zone());
+    next_block->statements()->Add(factory()->NewExpressionStatement(
+                                      parser_->BuildIteratorNextResult(
+                                          factory()->NewVariableProxy(iterator),
+                                          result, RelocInfo::kNoPosition),
+                                      RelocInfo::kNoPosition),
+                                  zone());
 
     auto assign_to_done = factory()->NewAssignment(
         Token::ASSIGN, factory()->NewVariableProxy(done),
         factory()->NewProperty(
             factory()->NewVariableProxy(result),
             factory()->NewStringLiteral(ast_value_factory()->done_string(),
                                         RelocInfo::kNoPosition),
             RelocInfo::kNoPosition),
         RelocInfo::kNoPosition);
     auto next_value = factory()->NewConditional(
@@ skipping 16 matching lines @@
         factory()->NewUnaryOperation(Token::NOT,
                                      factory()->NewVariableProxy(done),
                                      RelocInfo::kNoPosition),
         next_block, factory()->NewEmptyStatement(RelocInfo::kNoPosition),
         RelocInfo::kNoPosition);
     block_->statements()->Add(if_statement, zone());
 
     if (!(value->IsLiteral() && value->AsLiteral()->raw_value()->IsTheHole())) {
       RecurseIntoSubpattern(value, factory()->NewVariableProxy(v));
     }
+    set_context(context);
   }
 
   if (spread != nullptr) {
     // array = [];
     // if (!done) %concat_iterable_to_array(array, iterator);
     auto empty_exprs = new (zone()) ZoneList<Expression*>(0, zone());
     auto array = CreateTempVar(factory()->NewArrayLiteral(
         empty_exprs,
         // Reuse pattern's literal index - it is unused since there is no
         // actual literal allocated.
-        node->literal_index(), is_strong(descriptor_->parser->language_mode()),
+        node->literal_index(), is_strong(scope()->language_mode()),
         RelocInfo::kNoPosition));
 
     auto arguments = new (zone()) ZoneList<Expression*>(2, zone());
     arguments->Add(factory()->NewVariableProxy(array), zone());
     arguments->Add(factory()->NewVariableProxy(iterator), zone());
     auto spread_into_array_call =
         factory()->NewCallRuntime(Context::CONCAT_ITERABLE_TO_ARRAY_INDEX,
                                   arguments, RelocInfo::kNoPosition);
 
     auto if_statement = factory()->NewIfStatement(
         factory()->NewUnaryOperation(Token::NOT,
                                      factory()->NewVariableProxy(done),
                                      RelocInfo::kNoPosition),
         factory()->NewExpressionStatement(spread_into_array_call,
                                           RelocInfo::kNoPosition),
         factory()->NewEmptyStatement(RelocInfo::kNoPosition),
         RelocInfo::kNoPosition);
     block_->statements()->Add(if_statement, zone());
 
     RecurseIntoSubpattern(spread->expression(),
                           factory()->NewVariableProxy(array));
   }
 }
 
 
 void Parser::PatternRewriter::VisitAssignment(Assignment* node) {
-  // let {<pattern> = <init>} = <value>
-  //   becomes
-  // temp = <value>;
-  // <pattern> = temp === undefined ? <init> : temp;
+  if (node->destructuring_assignment()) return;
+
+  auto initializer = node->value();
+  auto value = initializer;
+  auto temp = CreateTempVar(current_value_);
+
+  if (IsInitializerContext()) {
+    // let {<pattern> = <init>} = <value>
+    //   becomes
+    // temp = <value>;
+    // <pattern> = temp === undefined ? <init> : temp;
+    Expression* is_undefined = factory()->NewCompareOperation(
+        Token::EQ_STRICT, factory()->NewVariableProxy(temp),
+        factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
+        RelocInfo::kNoPosition);
+    value = factory()->NewConditional(is_undefined, initializer,
+                                      factory()->NewVariableProxy(temp),
+                                      RelocInfo::kNoPosition);
+  }
+
+  PatternContext old_context = SetAssignmentContextIfNeeded(initializer);
+  if (node->is_destructuring_assignment() && IsAssignmentContext(old_context)) {
+    int pos = node->position();
+    Block* old_block = block_;
+    block_ = factory()->NewBlock(nullptr, 8, false, pos);
+    Variable* temp = nullptr;
+    Expression* pattern = node->target();
+    Expression* old_value = current_value_;
+    current_value_ = value;
+    if (pattern->IsObjectLiteral()) {
+      VisitObjectLiteral(pattern->AsObjectLiteral(), &temp);
+    } else {
+      DCHECK(pattern->IsArrayLiteral());
+      VisitArrayLiteral(pattern->AsArrayLiteral(), &temp);
+    }
+    DCHECK_NOT_NULL(temp);
+    current_value_ = old_value;
+    Expression* expr = factory()->NewDoExpression(block_, temp, pos);
+    node->set_destructuring_assignment(expr);
+    block_ = old_block;
+    if (block_) {
+      block_->statements()->Add(factory()->NewExpressionStatement(expr, pos),
+                                zone());
+    }
+    return set_context(old_context);
+  }
+
   DCHECK(node->op() == Token::ASSIGN);
-  auto temp = CreateTempVar(current_value_);
-  Expression* is_undefined = factory()->NewCompareOperation(
-      Token::EQ_STRICT, factory()->NewVariableProxy(temp),
-      factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
-      RelocInfo::kNoPosition);
-  Expression* initializer = node->value();
-  if (descriptor_->declaration_kind == DeclarationDescriptor::PARAMETER &&
-      descriptor_->scope->is_arrow_scope()) {
+  if (IsBindingContext(old_context) &&
+      descriptor_->declaration_kind == DeclarationDescriptor::PARAMETER &&
+      scope()->is_arrow_scope()) {
     // TODO(adamk): Only call this if necessary.
-    RewriteParameterInitializerScope(
-        descriptor_->parser->stack_limit(), initializer,
-        descriptor_->scope->outer_scope(), descriptor_->scope);
+    RewriteParameterInitializerScope(parser_->stack_limit(), initializer,
+                                     scope()->outer_scope(), scope());
   }
-  Expression* value = factory()->NewConditional(
-      is_undefined, initializer, factory()->NewVariableProxy(temp),
-      RelocInfo::kNoPosition);
   RecurseIntoSubpattern(node->target(), value);
+  set_context(old_context);
 }
 
 
+// =============== AssignmentPattern only ==================
+
+void Parser::PatternRewriter::VisitProperty(v8::internal::Property* node) {
+  DCHECK(IsAssignmentContext());
+  auto value = current_value_;
+
+  Assignment* assignment =
+      factory()->NewAssignment(Token::ASSIGN, node, value, node->position());
+
+  block_->statements()->Add(
+      factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+      zone());
+}
+
+
 // =============== UNREACHABLE =============================
 
 void Parser::PatternRewriter::Visit(AstNode* node) { UNREACHABLE(); }
 
 #define NOT_A_PATTERN(Node)                                        \
   void Parser::PatternRewriter::Visit##Node(v8::internal::Node*) { \
     UNREACHABLE();                                                 \
   }
 
 NOT_A_PATTERN(BinaryOperation)
@@ skipping 17 matching lines @@
 NOT_A_PATTERN(ExpressionStatement)
 NOT_A_PATTERN(ForInStatement)
 NOT_A_PATTERN(ForOfStatement)
 NOT_A_PATTERN(ForStatement)
 NOT_A_PATTERN(FunctionDeclaration)
 NOT_A_PATTERN(FunctionLiteral)
 NOT_A_PATTERN(IfStatement)
 NOT_A_PATTERN(ImportDeclaration)
 NOT_A_PATTERN(Literal)
 NOT_A_PATTERN(NativeFunctionLiteral)
-NOT_A_PATTERN(Property)
 NOT_A_PATTERN(RegExpLiteral)
 NOT_A_PATTERN(ReturnStatement)
 NOT_A_PATTERN(SloppyBlockFunctionStatement)
 NOT_A_PATTERN(Spread)
 NOT_A_PATTERN(SuperPropertyReference)
 NOT_A_PATTERN(SuperCallReference)
 NOT_A_PATTERN(SwitchStatement)
 NOT_A_PATTERN(ThisFunction)
 NOT_A_PATTERN(Throw)
 NOT_A_PATTERN(TryCatchStatement)
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8