dart2js: add support for configuration-specific imports.

pkg/compiler/lib/src/parser/parser.dart

 // 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.
 
 library dart2js.parser;
 
 import '../common.dart';
 import '../tokens/keyword.dart' show
     Keyword;
 import '../tokens/precedence.dart' show
@@ skipping 80 matching lines @@
  *
  * Parse methods are generally named parseGrammarProductionSuffix. The
  * suffix can be one of "opt", or "star". "opt" means zero or one
  * matches, "star" means zero or more matches. For example,
  * [parseMetadataStar] corresponds to this grammar snippet: [:
  * metadata* :], and [parseTypeOpt] corresponds to: [: type? :].
  */
 class Parser {
   final Listener listener;
   bool mayParseFunctionExpressions = true;
+  final bool enableConditionalDirectives;
   bool asyncAwaitKeywordsEnabled;
 
   Parser(this.listener,
-         {this.asyncAwaitKeywordsEnabled: false});
+      {this.enableConditionalDirectives: false,
+       this.asyncAwaitKeywordsEnabled: false});
 
   Token parseUnit(Token token) {
     listener.beginCompilationUnit(token);
     int count = 0;
     while (!identical(token.kind, EOF_TOKEN)) {
       token = parseTopLevelDeclaration(token);
       listener.endTopLevelDeclaration(token);
       count++;
     }
     listener.endCompilationUnit(count, token);
@@ skipping 28 matching lines @@
     Token libraryKeyword = token;
     listener.beginLibraryName(libraryKeyword);
     assert(optional('library', token));
     token = parseQualified(token.next);
     Token semicolon = token;
     token = expect(';', token);
     listener.endLibraryName(libraryKeyword, semicolon);
     return token;
   }
 
-  /// import uri (as identifier)? combinator* ';'
+  /// import uri (if (test) uri)* (as identifier)? combinator* ';'
   Token parseImport(Token token) {
     Token importKeyword = token;
     listener.beginImport(importKeyword);
     assert(optional('import', token));
     token = parseLiteralStringOrRecoverExpression(token.next);
+    token = parseConditionalUris(token);
     Token deferredKeyword;
     if (optional('deferred', token)) {
       deferredKeyword = token;
       token = token.next;
     }
     Token asKeyword;
     if (optional('as', token)) {
       asKeyword = token;
       token = parseIdentifier(token.next);
     }
     token = parseCombinators(token);
     Token semicolon = token;
     token = expect(';', token);
     listener.endImport(importKeyword, deferredKeyword, asKeyword, semicolon);
     return token;
   }
 
-  /// export uri combinator* ';'
+  /// if (test) uri
+  Token parseConditionalUris(Token token) {
+    listener.beginConditionalUris(token);
+    int count = 0;
+    if (enableConditionalDirectives) {
+      while (optional('if', token)) {
+        count++;
+        token = parseConditionalUri(token);
+      }
+    }
+    listener.endConditionalUris(count);
+    return token;
+  }
+
+  Token parseConditionalUri(Token token) {
+    listener.beginConditionalUri(token);
+    Token ifKeyword = token;
+    token = expect('if', token);
+    token = expect('(', token);
+    token = parseDottedName(token);
+    Token equalitySign;
+    if (optional('==', token)) {
+      equalitySign = token;
+      token = parseLiteralStringOrRecoverExpression(token.next);
+    }
+    token = expect(')', token);
+    token = parseLiteralStringOrRecoverExpression(token);
+    listener.endConditionalUri(ifKeyword, equalitySign);
+    return token;
+  }
+
+  Token parseDottedName(Token token) {
+    listener.beginDottedName(token);
+    Token firstIdentifier = token;
+    token = parseIdentifier(token);
+    int count = 1;
+    while (optional('.', token)) {
+      token = parseIdentifier(token.next);
+      count++;
+    }
+    listener.endDottedName(count, firstIdentifier);
+    return token;
+  }
+
+  /// export uri conditional-uris* combinator* ';'
   Token parseExport(Token token) {
     Token exportKeyword = token;
     listener.beginExport(exportKeyword);
     assert(optional('export', token));
     token = parseLiteralStringOrRecoverExpression(token.next);
+    token = parseConditionalUris(token);
     token = parseCombinators(token);
     Token semicolon = token;
     token = expect(';', token);
     listener.endExport(exportKeyword, semicolon);
     return token;
   }
 
   Token parseCombinators(Token token) {
     listener.beginCombinators(token);
     int count = 0;
@@ skipping 2542 matching lines @@
     }
     listener.handleContinueStatement(hasTarget, continueKeyword, token);
     return expectSemicolon(token);
   }
 
   Token parseEmptyStatement(Token token) {
     listener.handleEmptyStatement(token);
     return expectSemicolon(token);
   }
 }