Add support for parsing comments with generic parameters /*<K, V>*/ 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 e6dba6a39dc1d8cd5fc6c8321fba028110f6bda5..ecf6fc15339d4f334ec5a4e9a6b0bb794b508bf3 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -65,7 +65,10 @@ import '../scanner/precedence.dart'
         ASSIGNMENT_PRECEDENCE,
         AS_INFO,
         CASCADE_PRECEDENCE,
+        EOF_INFO,
         EQUALITY_PRECEDENCE,
+        GENERIC_METHOD_TYPE_ASSIGN,
+        GENERIC_METHOD_TYPE_LIST,
         GT_INFO,
         IS_INFO,
         MINUS_MINUS_INFO,
@@ -83,6 +86,7 @@ import '../scanner/precedence.dart'
 import '../scanner/token.dart'
     show
         BeginGroupToken,
+        CommentToken,
         KeywordToken,
         SymbolToken,
         Token,
@@ -113,6 +117,7 @@ import '../scanner/token_constants.dart'
         STRING_TOKEN;
 
 import '../scanner/characters.dart' show $CLOSE_CURLY_BRACKET;
+import '../scanner/string_scanner.dart';

[ahe, 2017/04/04 08:10:45]

The parser shouldn't be importing as specific scanner.

[scheglov, 2017/04/04 15:33:47]

Why?
The parser knows what it wants to parse and how.

 
 import '../util/link.dart' show Link;
 
@@ -184,6 +189,8 @@ class Parser {
 
   bool mayParseFunctionExpressions = true;
 
+  bool parseGenericMethodComments = false;
+
   /// Represents parser state: what asynchronous syntax is allowed in the
   /// function being currently parsed. In rare situations, this can be set by
   /// external clients, for example, to parse an expression outside a function.
@@ -633,6 +640,7 @@ class Parser {
       }
     }
 
+    token = _injectGenericCommentTypeList(token);

[ahe, 2017/04/04 08:10:45]

This method should be public and overridden in a subclass.

[scheglov, 2017/04/04 15:33:47]

In which subclass?

     if (optional('(', token)) {
       Token inlineFunctionTypeStart = token;
       listener.beginFunctionTypedFormalParameter(token);
@@ -1107,9 +1115,10 @@ class Parser {
         (t) => listener.handleNoTypeVariables(t));
   }
 
-  // TODO(ahe): Clean this up.
+  /// TODO(ahe): Clean this up.

[ahe, 2017/04/04 08:10:45]

This isn't a documentation comment.

[scheglov, 2017/04/04 15:33:47]

Well, I think any comment before a method, and which is related to the method,
should be a documentation comment.

   Token parseStuff(Token token, Function beginStuff, Function stuffParser,
       Function endStuff, Function handleNoStuff) {
+    token = _injectGenericCommentTypeList(token);
     if (optional('<', token)) {
       Token begin = token;
       beginStuff(begin);
@@ -2788,6 +2797,7 @@ class Parser {
   }
 
   Token parsePrimary(Token token, IdentifierContext context) {
+    token = _injectGenericCommentTypeList(token);
     final kind = token.kind;
     if (kind == IDENTIFIER_TOKEN) {
       return parseSendOrFunctionLiteral(token, context);
@@ -3080,6 +3090,7 @@ class Parser {
   Token parseConstExpression(Token token) {
     Token constKeyword = token;
     token = expect('const', token);
+    token = _injectGenericCommentTypeList(token);
     final String value = token.stringValue;
     if ((identical(value, '[')) || (identical(value, '[]'))) {
       listener.handleNoTypeArguments(token);
@@ -3193,6 +3204,7 @@ class Parser {
     Token beginToken = token;
     listener.beginSend(token);
     token = parseIdentifier(token, context);
+    token = _injectGenericCommentTypeList(token);
     if (isValidMethodTypeArguments(token)) {
       token = parseTypeArgumentsOpt(token);
     } else {
@@ -3789,6 +3801,60 @@ class Parser {
     return reportUnrecoverableError(
         token, () => code.format(uri, token.charOffset, string));
   }
+
+  /// Matches a generic comment type parameters or type arguments and injects
+  /// them into the token stream before the given [token].
+  Token _injectGenericCommentTypeList(Token token) {
+    return _injectGenericComment(token, GENERIC_METHOD_TYPE_LIST, 2);
+  }
+
+  /// Check if the given [token] has a comment token with the given [info],
+  /// which should be either [GENERIC_METHOD_TYPE_ASSIGN] or
+  /// [GENERIC_METHOD_TYPE_LIST].  If found, parse the comment into tokens and
+  /// inject into the token stream before the [token].
+  Token _injectGenericComment(Token token, PrecedenceInfo info, int prefixLen) {
+    if (parseGenericMethodComments) {
+      CommentToken t = token.precedingCommentTokens;
+      for (; t != null; t = t.next) {
+        if (t.info == info) {
+          String code = t.lexeme.substring(prefixLen, t.lexeme.length - 2);
+          Token tokens = _scanGenericMethodComment(code, t.offset + prefixLen);
+          if (tokens != null) {
+            // Remove the token from the comment stream.
+            t.remove();
+            // Insert the tokens into the stream.
+            _injectTokenList(token, tokens);
+            return tokens;
+          }
+        }
+      }
+    }
+    return token;
+  }
+
+  /// Scans the given [code], and returns the tokens, otherwise returns `null`.
+  Token _scanGenericMethodComment(String code, int offset) {
+    // TODO(scheglov) Let StringScanner to specify the string offset.
+    var scanner = new StringScanner(' ' * offset + code);

[ahe, 2017/04/04 08:10:45]

The listener should be asked how to create a scanner, otherwise you can't extend
it.

[scheglov, 2017/04/04 15:33:47]

What do we want to extend?
These comments are part of the language, and should be supported in the parser
for the language.

+    Token firstToken = scanner.tokenize();
+    if (scanner.hasErrors) {
+      return null;
+    }
+    return firstToken;
+  }
+
+  void _injectTokenList(Token beforeToken, Token firstToken) {
+    // Scanner creates a cyclic EOF token.
+    Token lastToken = firstToken;
+    while (lastToken.next.info != EOF_INFO) {
+      lastToken = lastToken.next;
+    }
+    // Inject these new tokens into the stream.
+    Token previous = beforeToken.previous;
+    lastToken.setNext(beforeToken);
+    previous.setNext(firstToken);
+    beforeToken = firstToken;
+  }
 }
 
 typedef FastaMessage NoArgument(Uri uri, int charOffset);