After parsing a ':' in an enum-specifier within class context,

disambiguate between an expression (for a bit-field width) and a type
(for a fixed underlying type). Since the disambiguation can be
expensive (due to tentative parsing), we perform a simplistic
disambiguation based on one-token lookahead before going into the
full-blown tentative parsing. Based on a patch by Daniel Wallin.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@120582 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 50 insertions, 4 deletions

diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index db02c78351..f1fb7b29a1 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -1921,7 +1921,6 @@ void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
   Actions.ActOnTagFinishDefinition(getCurScope(), TagDecl, RBraceLoc);
 }
 
-
 /// ParseEnumSpecifier
 ///       enum-specifier: [C99 6.7.2.2]
 ///         'enum' identifier[opt] '{' enumerator-list '}'
@@ -2014,10 +2013,57 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
 
   TypeResult BaseType;
 
+  // Parse the fixed underlying type.
   if (getLang().CPlusPlus0x && Tok.is(tok::colon)) {
-    ConsumeToken();
-    SourceRange Range;
-    BaseType = ParseTypeName(&Range);
+    bool PossibleBitfield = false;
+    if (getCurScope()->getFlags() & Scope::ClassScope) {
+      // If we're in class scope, this can either be an enum declaration with
+      // an underlying type, or a declaration of a bitfield member. We try to
+      // use a simple disambiguation scheme first to catch the common cases
+      // (integer literal, sizeof); if it's still ambiguous, we then consider 
+      // anything that's a simple-type-specifier followed by '(' as an 
+      // expression. This suffices because function types are not valid 
+      // underlying types anyway.
+      TPResult TPR = isExpressionOrTypeSpecifierSimple(NextToken().getKind());
+      // If the next token starts an expression, we know we're parsing a 
+      // bit-field. This is the common case.
+      if (TPR == TPResult::True())
+        PossibleBitfield = true;
+      // If the next token starts a type-specifier-seq, it may be either a
+      // a fixed underlying type or the start of a function-style cast in C++;
+      // lookahead one more token to see if it's obvious that we have a 
+      // fixed underlying type.
+      else if (TPR == TPResult::False() && 
+               GetLookAheadToken(2).getKind() == tok::semi) {
+        // Consume the ':'.
+        ConsumeToken();
+      } else {
+        // We have the start of a type-specifier-seq, so we have to perform
+        // tentative parsing to determine whether we have an expression or a
+        // type.
+        TentativeParsingAction TPA(*this);
+
+        // Consume the ':'.
+        ConsumeToken();
+      
+        if (isCXXDeclarationSpecifier() != TPResult::True()) {
+          // We'll parse this as a bitfield later.
+          PossibleBitfield = true;
+          TPA.Revert();
+        } else {
+          // We have a type-specifier-seq.
+          TPA.Commit();
+        }
+      }
+    } else {
+      // Consume the ':'.
+      ConsumeToken();
+    }
+
+    if (!PossibleBitfield) {
+      SourceRange Range;
+      BaseType = ParseTypeName(&Range);
+    }
   }
 
   // There are three options here.  If we have 'enum foo;', then this is a