Optimize away empty string sections in string interpolation

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 3377 matching lines @@
                              current_class(),
                              field->name_pos);
     class_field.set_type(*field->type);
     class_field.set_has_initializer(has_initializer);
     members->AddField(class_field);
     if (field->metadata_pos >= 0) {
       library_.AddFieldMetadata(class_field, field->metadata_pos);
     }
 
     // For static final fields (this includes static const fields), set value to
-    // "uninitialized" and create a kFinalImplicitGetter getter method.
+    // "uninitialized" and create a kImplicitStaticFinalGetter getter method.
     if (field->has_static && has_initializer) {
       class_field.set_value(init_value);
       if (!has_simple_literal) {
         String& getter_name = String::Handle(Field::GetterSymbol(*field->name));
         getter = Function::New(getter_name,
                                RawFunction::kImplicitStaticFinalGetter,
                                field->has_static,
                                field->has_const,
                                /* is_abstract = */ false,
                                /* is_external = */ false,
@@ skipping 6629 matching lines @@
       (l1_token != Token::kINTERPOL_START)) {
     // Common case: no interpolation.
     primary = new LiteralNode(literal_start, *CurrentLiteral());
     ConsumeToken();
     return primary;
   }
   // String interpolation needed.
   bool is_compiletime_const = true;
   GrowableArray<AstNode*> values_list;
   while (CurrentToken() == Token::kSTRING) {
-    values_list.Add(new LiteralNode(TokenPos(), *CurrentLiteral()));
+    if (CurrentLiteral()->Length() > 0) {
+      // Only add non-empty string sections to the values list
+      // that will be concatenated.
+      values_list.Add(new LiteralNode(TokenPos(), *CurrentLiteral()));
+    }
     ConsumeToken();
     while ((CurrentToken() == Token::kINTERPOL_VAR) ||
         (CurrentToken() == Token::kINTERPOL_START)) {
       AstNode* expr = NULL;
       const intptr_t expr_pos = TokenPos();
       if (CurrentToken() == Token::kINTERPOL_VAR) {
         expr = ResolveIdent(TokenPos(), *CurrentLiteral(), true);
         ConsumeToken();
       } else {
         ASSERT(CurrentToken() == Token::kINTERPOL_START);
@@ skipping 556 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart