Parse type substitution comments /*=T*/ in variable declarations with Fasta.

pkg/front_end/lib/src/fasta/parser/parser.dart

Index: pkg/front_end/lib/src/fasta/parser/parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/parser.dart b/pkg/front_end/lib/src/fasta/parser/parser.dart
index f323b4519c356cb29e55355deacd0e461ec1286a..229b72eaf4c8bf1c97a1eea4ccc7931af8f9b5a5 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -726,6 +726,7 @@ class Parser {
       // Function type without return type.
       return parseType(token);
     }
+    token = _injectGenericCommentTypeAssign(token);

[ahe, 2017/04/06 08:58:38]

Methods in the parser needs to be public so they can be overridden by
subclasses.

[ahe, 2017/04/06 10:04:42]

See CL 2799043004 for a detailed explanation.

[scheglov, 2017/04/06 16:15:55]

I moved these methods to Listener.

     Token peek = peekAfterIfType(token);
     if (peek != null && (peek.isIdentifier() || optional('this', peek))) {
       return parseType(token);
@@ -2405,6 +2406,12 @@ class Parser {
     Token identifier = peekIdentifierAfterType(token);
     if (identifier != null) {
       assert(identifier.isIdentifier());
+
+      // If the identifier token has a type substitution comment /*=T*/,
+      // then the set of tokens type tokens should be replaced with the
+      // tokens parsed from the comment.
+      token = _replaceTokenWithGenericCommentTypeAssign(token, identifier);
+
       Token afterId = identifier.next;
       int afterIdKind = afterId.kind;
       if (identical(afterIdKind, EQ_TOKEN) ||
@@ -2489,6 +2496,7 @@ class Parser {
     if (isModifier(token.next)) {
       return parseVariablesDeclaration(token);
     }
+    _injectGenericCommentTypeAssign(token.next);
     Token identifier = peekIdentifierAfterOptionalType(token.next);
     if (identifier != null) {
       assert(identifier.isIdentifier());
@@ -3310,6 +3318,13 @@ class Parser {
       Token token, bool endWithSemicolon) {
     int count = 1;
     token = parseMetadataStar(token);
+
+    // If the next token has a type substitution comment /*=T*/, then
+    // the current 'var' token should be repealed and replaced.
+    if (token.keyword == Keyword.VAR) {

[ahe, 2017/04/06 08:58:38]

Use this method to match keywords:

optional('var', token)

[ahe, 2017/04/06 10:04:42]

See lines 178-184.

[scheglov, 2017/04/06 16:15:55]

Done.

+      token = _replaceTokenWithGenericCommentTypeAssign(token, token.next);
+    }
+
     token = parseModifiers(token);
     token = parseTypeOpt(token);
     listener.beginVariablesDeclaration(token);
@@ -3803,6 +3818,12 @@ class Parser {
         token, () => code.format(uri, token.charOffset, string));
   }
 
+  /// Matches a generic comment type substitution and injects it into the token
+  /// stream before the given [token].
+  Token _injectGenericCommentTypeAssign(Token token) {
+    return _injectGenericComment(token, GENERIC_METHOD_TYPE_ASSIGN, 3);
+  }
+
   /// Matches a generic comment type parameters or type arguments and injects
   /// them into the token stream before the given [token].
   Token _injectGenericCommentTypeList(Token token) {
@@ -3855,6 +3876,23 @@ class Parser {
     previous.setNext(firstToken);
     beforeToken = firstToken;
   }
+
+  /// If the [tokenWithComment] has a type substitution comment /*=T*/, then
+  /// the comment should be scanned into new tokens, and these tokens inserted
+  /// instead of tokens from the [tokenToStartReplacing] to the
+  /// [tokenWithComment]. Returns the first newly inserted token, or the
+  /// original [tokenWithComment].
+  Token _replaceTokenWithGenericCommentTypeAssign(
+      Token tokenToStartReplacing, Token tokenWithComment) {
+    Token injected = _injectGenericCommentTypeAssign(tokenWithComment);
+    if (!identical(injected, tokenWithComment)) {
+      Token prev = tokenToStartReplacing.previous;
+      prev.setNextWithoutSettingPrevious(injected);
+      tokenToStartReplacing = injected;
+      tokenToStartReplacing.previous = prev;
+    }
+    return tokenToStartReplacing;
+  }
 }
 
 typedef FastaMessage NoArgument(Uri uri, int charOffset);