[ESnext] Implement Object Rest

src/parsing/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/ast.h"
 #include "src/messages.h"
 #include "src/objects-inl.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
 #include "src/parsing/parser.h"
 
@@ skipping 314 matching lines @@
   DCHECK(scope()->outer_scope()->is_function_scope());
   DCHECK(scope()->calls_sloppy_eval());
 
   ReparentParameterExpressionScope(parser_->stack_limit(), expr, scope());
 }
 
 void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern,
                                                  Variable** temp_var) {
   auto temp = *temp_var = CreateTempVar(current_value_);
 
+  ZoneList<Expression*>* excluded_properties;
+  if (pattern->has_rest_property()) {
+    int non_rest_properties = pattern->properties()->length() - 1;
+    excluded_properties =
+        new (zone()) ZoneList<Expression*>(non_rest_properties, zone());
+  } else {
+    excluded_properties = new (zone()) ZoneList<Expression*>(0, zone());
+  }
+
   block_->statements()->Add(parser_->BuildAssertIsCoercible(temp), zone());
 
   for (ObjectLiteralProperty* property : *pattern->properties()) {
     PatternContext context = SetInitializerContextIfNeeded(property->value());
+    Expression* value;
 
-    // Computed property names contain expressions which might require
-    // scope rewriting.
-    if (!property->key()->IsLiteral()) RewriteParameterScopes(property->key());
+    if (property->kind() == ObjectLiteralProperty::Kind::SPREAD) {
+      // var { a, b, ...c } = temp
+      //     becomes
+      // var c;
+      // c = %CopyDataProperties(temp, [a, b]);

[adamk, 2017/01/10 23:22:56]

Can you add something about the desugaring of computed property names?

[gsathya, 2017/01/12 21:27:41]

There's a comment below where I handle the computed property name. Do you want
the desugaring to show the temporary variable creation?

[adamk, 2017/01/12 22:43:08]

Yeah, I was thinking that this should basically read like an example from your
design doc, with the desugaring including the computed property case.

+      auto args = new (zone()) ZoneList<Expression*>(2, zone());
+      args->Add(factory()->NewVariableProxy(temp), zone());
+      args->Add(
+          factory()->NewArrayLiteral(
+              excluded_properties, pattern->literal_index(), kNoSourcePosition),
+          zone());
 
-    RecurseIntoSubpattern(
-        property->value(),
-        factory()->NewProperty(factory()->NewVariableProxy(temp),
-                               property->key(), kNoSourcePosition));
+      value = factory()->NewCallRuntime(
+          Runtime::kCopyDataPropertiesWithExcludedProperties, args,
+          kNoSourcePosition);
+    } else {
+      Expression* key = property->key();
+
+      if (!key->IsLiteral()) {
+        // Computed property names contain expressions which might require
+        // scope rewriting.
+        RewriteParameterScopes(key);
+
+        // We create a temporary variable for a computed property name
+        // so that we don't evaluate it twice when we include it in
+        // the excluded_properties list.
+        key = factory()->NewVariableProxy(CreateTempVar(key));

[adamk, 2017/01/10 23:22:56]

You need to assign CreateTempVar to something so that you can create multiple
VariableProxies referencing it.

And I think you only want to create this temp var if we have a rest property,
right?

[gsathya, 2017/01/12 21:27:41]

Done.

+      }
+
+      if (pattern->has_rest_property()) {
+        excluded_properties->Add(key, zone());

[adamk, 2017/01/10 23:22:56]

As noted above, this needs to be a NewVariableProxy(temp)

[gsathya, 2017/01/12 21:27:41]

Done.

+      }
+
+      value = factory()->NewProperty(factory()->NewVariableProxy(temp), key,
+                                     kNoSourcePosition);
+    }
+
+    RecurseIntoSubpattern(property->value(), value);
     set_context(context);
   }
 }
 
 
 void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* node) {
   Variable* temp_var = nullptr;
   VisitObjectLiteral(node, &temp_var);
 }
 
@@ skipping 334 matching lines @@
 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