[es6] implement destructuring assignment

src/parsing/parser.cc

 // Copyright 2012 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/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
+#include "src/ast/ast-expression-visitor.h"
 #include "src/ast/ast-literal-reindexer.h"
 #include "src/ast/scopeinfo.h"
 #include "src/bailout-reason.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
 #include "src/char-predicates-inl.h"
 #include "src/codegen.h"
 #include "src/compiler.h"
 #include "src/messages.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
@@ skipping 894 matching lines @@
   // ParseInfo during background parsing.
   DCHECK(!info->script().is_null() || info->source_stream() != NULL);
   set_allow_lazy(info->allow_lazy_parsing());
   set_allow_natives(FLAG_allow_natives_syntax || info->is_native());
   set_allow_harmony_sloppy(FLAG_harmony_sloppy);
   set_allow_harmony_sloppy_function(FLAG_harmony_sloppy_function);
   set_allow_harmony_sloppy_let(FLAG_harmony_sloppy_let);
   set_allow_harmony_rest_parameters(FLAG_harmony_rest_parameters);
   set_allow_harmony_default_parameters(FLAG_harmony_default_parameters);
   set_allow_harmony_destructuring_bind(FLAG_harmony_destructuring_bind);
+  set_allow_harmony_destructuring_assignment(
+      FLAG_harmony_destructuring_assignment);
   set_allow_strong_mode(FLAG_strong_mode);
   set_allow_legacy_const(FLAG_legacy_const);
   set_allow_harmony_do_expressions(FLAG_harmony_do_expressions);
   for (int feature = 0; feature < v8::Isolate::kUseCounterFeatureCount;
        ++feature) {
     use_counts_[feature] = 0;
   }
   if (info->ast_value_factory() == NULL) {
     // info takes ownership of AstValueFactory.
     info->set_ast_value_factory(new AstValueFactory(zone(), info->hash_seed()));
@@ skipping 150 matching lines @@
       if (body->length() != 1 ||
           !body->at(0)->IsExpressionStatement() ||
           !body->at(0)->AsExpressionStatement()->
               expression()->IsFunctionLiteral()) {
         ReportMessage(MessageTemplate::kSingleFunctionLiteral);
         ok = false;
       }
     }
 
     if (ok) {
+      ParserTraits::RewriteDestructuringAssignments();
       result = factory()->NewFunctionLiteral(
           ast_value_factory()->empty_string(), ast_value_factory(), scope_,
           body, function_state.materialized_literal_count(),
           function_state.expected_property_count(), 0,
           FunctionLiteral::kNoDuplicateParameters,
           FunctionLiteral::ANONYMOUS_EXPRESSION, FunctionLiteral::kGlobalOrEval,
           FunctionLiteral::kShouldLazyCompile, FunctionKind::kNormalFunction,
           0);
     }
   }
@@ skipping 3287 matching lines @@
       CheckStrictOctalLiteral(scope->start_position(), scope->end_position(),
                               CHECK_OK);
     }
     if (is_sloppy(language_mode) && allow_harmony_sloppy_function()) {
       InsertSloppyBlockFunctionVarBindings(scope, CHECK_OK);
     }
     if (is_strict(language_mode) || allow_harmony_sloppy() ||
         allow_harmony_destructuring_bind()) {
       CheckConflictingVarDeclarations(scope, CHECK_OK);
     }
+
+    if (body) {
+      // If body can be inspected, rewrite queued destructuring assignments
+      ParserTraits::RewriteDestructuringAssignments();
+    }
   }
 
   bool has_duplicate_parameters =
       !formals_classifier.is_valid_formal_parameter_list_without_duplicates();
   FunctionLiteral::ParameterFlag duplicate_parameters =
       has_duplicate_parameters ? FunctionLiteral::kHasDuplicateParameters
                                : FunctionLiteral::kNoDuplicateParameters;
 
   FunctionLiteral* function_literal = factory()->NewFunctionLiteral(
       function_name, ast_value_factory(), scope, body,
@@ skipping 108 matching lines @@
       RelocInfo::kNoPosition);
   IfStatement* if_statement = factory()->NewIfStatement(
       condition, factory()->NewExpressionStatement(throw_type_error,
                                                    RelocInfo::kNoPosition),
       factory()->NewEmptyStatement(RelocInfo::kNoPosition),
       RelocInfo::kNoPosition);
   return if_statement;
 }
 
 
+class InitializerRewriter : public AstExpressionVisitor {
+ public:
+  InitializerRewriter(uintptr_t stack_limit, Expression* root, Parser* parser,
+                      Scope* scope)
+      : AstExpressionVisitor(stack_limit, root),
+        parser_(parser),
+        scope_(scope) {}
+
+ private:
+  void VisitExpression(Expression* expr) {
+    RewritableExpression* rw = expr->AsRewritableExpression();

[adamk, 2015/12/01 22:42:56]

Naming nit: I like "to_rewrite" better than "rw".

+    if (!rw ||

[adamk, 2015/12/01 22:42:56]

to_rewrite == nullptr

+        !rw->IsRewritableAs(RewritableExpression::kDestructuringAssignment)) {

[adamk, 2015/12/01 22:42:56]

It's checks like this that I don't see as terribly useful, since they're always
true.

[caitp (gmail), 2015/12/01 22:51:00]

the check is checking 2 things: 1, that it's "possibly" a destructuring
assignment (eg, valid syntax), and 2, that it hasn't already been rewritten as a
destructuring assignment.

While the first check could probably go away until more things need to use it
(which hopefully never happens, admittedly), the second one is pretty important
to make sure there's no endless looping (or hitting UNREACHABLEs and crashing)

[adamk, 2015/12/01 22:54:23]

Right, sorry, there is that second case. Even so, I think it's more
understandable if the only reason something would fail this check was if it's
already been rewritten.

+      return;
+    }
+
+    bool ok = true;
+    Parser::PatternRewriter::RewriteDestructuringAssignment(parser_, rw, scope_,
+                                                            &ok);
+    DCHECK(ok);
+  }
+
+ private:
+  Parser* parser_;
+  Scope* scope_;
+};
+
+
+void Parser::RewriteParameterInitializer(Expression* expr, Scope* scope) {
+  InitializerRewriter rewriter(stack_limit_, expr, this, scope);
+  rewriter.Run();
+}
+
+
 Block* Parser::BuildParameterInitializationBlock(
     const ParserFormalParameters& parameters, bool* ok) {
   DCHECK(!parameters.is_simple);
   DCHECK(scope_->is_function_scope());
   Block* init_block =
       factory()->NewBlock(NULL, 1, true, RelocInfo::kNoPosition);
   for (int i = 0; i < parameters.params.length(); ++i) {
     auto parameter = parameters.params[i];
     DeclarationDescriptor descriptor;
     descriptor.declaration_kind = DeclarationDescriptor::PARAMETER;
@@ skipping 12 matching lines @@
     // it's just copying from a temp var to the real param var?
     descriptor.initialization_pos = parameter.pattern->position();
     // The initializer position which will end up in,
     // Variable::initializer_position(), used for hole check elimination.
     int initializer_position = parameter.pattern->position();
     Expression* initial_value =
         factory()->NewVariableProxy(parameters.scope->parameter(i));
     if (parameter.initializer != nullptr) {
       // IS_UNDEFINED($param) ? initializer : $param
       DCHECK(!parameter.is_rest);
+
+      // Ensure initializer is rewritten
+      RewriteParameterInitializer(parameter.initializer, scope_);
+
       auto condition = factory()->NewCompareOperation(
           Token::EQ_STRICT,
           factory()->NewVariableProxy(parameters.scope->parameter(i)),
           factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
           RelocInfo::kNoPosition);
       initial_value = factory()->NewConditional(
           condition, parameter.initializer, initial_value,
           RelocInfo::kNoPosition);
       descriptor.initialization_pos = parameter.initializer->position();
       initializer_position = parameter.initializer_end_position;
@@ skipping 1883 matching lines @@
   ++use_counts_[feature];
   scope->SetLanguageMode(mode);
 }
 
 
 void Parser::RaiseLanguageMode(LanguageMode mode) {
   SetLanguageMode(scope_,
                   static_cast<LanguageMode>(scope_->language_mode() | mode));
 }
 
+
+void ParserTraits::RewriteDestructuringAssignments() {
+  parser_->RewriteDestructuringAssignments();
+}
+
+
+void Parser::RewriteDestructuringAssignments() {
+  FunctionState* func = function_state_;
+  if (!allow_harmony_destructuring_assignment()) return;
+  const List<DestructuringAssignment>& assignments =
+      func->destructuring_assignments_to_rewrite();
+  for (int i = assignments.length() - 1; i >= 0; --i) {
+    // Rewrite list in reverse, so that nested assignment patterns are rewritten
+    // correctly.
+    DestructuringAssignment pair = assignments.at(i);
+    RewritableExpression* rw = pair.assignment->AsRewritableExpression();

[adamk, 2015/12/01 22:42:56]

Like the old name better here too

+    Scope* scope = pair.scope;
+    DCHECK_NOT_NULL(rw);
+    if (rw->IsRewritableAs(RewritableExpression::kDestructuringAssignment)) {
+      bool ok = true;
+      PatternRewriter::RewriteDestructuringAssignment(this, rw, scope, &ok);
+      DCHECK(ok);
+    }
+  }
+}
+
+
+void ParserTraits::QueueDestructuringAssignmentForRewriting(Expression* expr) {
+  DCHECK(expr->IsRewritableExpression());
+  DCHECK(expr->AsRewritableExpression()->expression()->IsAssignment());

[adamk, 2015/12/01 22:42:56]

This, too, will go away if you just use the C++ type Assignment in
RewritableExpression.

+  DCHECK(expr->AsRewritableExpression()->hints() &
+         RewritableExpression::kDestructuringAssignment);
+  parser_->function_state_->AddDestructuringAssignment(
+      Parser::DestructuringAssignment(expr, parser_->scope_));
+}
+
+
 }  // namespace internal
 }  // namespace v8