Don't peek when parsing mixin applications.

pkg/front_end/lib/src/fasta/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 fasta.parser.parser;
 
 import '../fasta_codes.dart'
     show
         FastaCode,
         FastaMessage,
@@ skipping 619 matching lines @@
     } else {
       token = afterType;
       token = parseIdentifier(token, IdentifierContext.typedefDeclaration);
       token = parseTypeVariablesOpt(token);
       token = parseFormalParameters(token, MemberKind.FunctionTypeAlias);
     }
     listener.endFunctionTypeAlias(typedefKeyword, equals, token);
     return expect(';', token);
   }
 
-  Token parseMixinApplication(Token token) {
+  /// Parse a mixin application starting from `with`. Assumes that the first
+  /// type has already been parsed.
+  Token parseMixinApplicationRest(Token token) {
     listener.beginMixinApplication(token);
-    token = parseType(token);
     Token withKeyword = token;
     token = expect('with', token);
     token = parseTypeList(token);
     listener.endMixinApplication(withKeyword);
     return token;
   }
 
   Token parseFormalParametersOpt(Token token, MemberKind kind) {
     if (optional('(', token)) {
       return parseFormalParameters(token, kind);
@@ skipping 342 matching lines @@
       return parseNamedMixinApplication(
           token, begin, classKeyword, name, equals);
     } else {
       listener.beginClassDeclaration(begin, name);
       return parseClass(token, begin, classKeyword, name);
     }
   }
 
   Token parseNamedMixinApplication(
       Token token, Token begin, Token classKeyword, Token name, Token equals) {
-    token = parseMixinApplication(token);
+    token = parseType(token);
+    token = parseMixinApplicationRest(token);
     Token implementsKeyword = null;
     if (optional('implements', token)) {
       implementsKeyword = token;
       token = parseTypeList(token.next);
     }
     listener.endNamedMixinApplication(
         begin, classKeyword, equals, implementsKeyword, token);
     return expect(';', token);
   }
 
   Token parseClass(Token token, Token begin, Token classKeyword, Token name) {

[danrubel, 2017/06/24 22:18:51]

nit: "name" parameter is never used

[ahe, 2017/06/26 11:18:16]

I'll address this in the next CL. After you pointed this out, I realized that I
can remove several parameters to parseNamedMixinApplication as well.

     Token extendsKeyword;
     if (optional('extends', token)) {
       extendsKeyword = token;
-      if (optional('with', peekAfterNominalType(token.next))) {
-        token = parseMixinApplication(token.next);
-      } else {
-        token = parseType(token.next);
+      token = parseType(token.next);
+      if (optional('with', token)) {
+        token = parseMixinApplicationRest(token);
       }
     } else {
       extendsKeyword = null;
       listener.handleNoType(token);
     }
     Token implementsKeyword;
     int interfacesCount = 0;
     if (optional('implements', token)) {
       implementsKeyword = token;
       do {
@@ skipping 2998 matching lines @@
     return reportUnrecoverableError(
         token, () => code.format(uri, token.charOffset, string));
   }
 }
 
 typedef FastaMessage NoArgument(Uri uri, int charOffset);
 
 typedef FastaMessage TokenArgument(Uri uri, int charOffset, Token token);
 
 typedef FastaMessage StringArgument(Uri uri, int charOffset, String string);