Support offset of member designator with the arrow for __builtin_offsetof

[Jim]

Summary

Push array index 0 into offsets to support offset of member designator x->b.

[efriedma]

Testcase?

I assume we give appropriate errors if you try to use "->" on a member that's not an array?

clang/lib/Parse/ParseExpr.cpp

2168

Did you fix this FIXME? Or does it no longer apply?

clang/lib/Parse/ParseExpr.cpp

case tok::kw___builtin_offsetof: {
     // Keep track of the various subcomponents we see.
     SmallVector<Sema::OffsetOfComponent, 4> Comps;
 
     Comps.push_back(Sema::OffsetOfComponent());
     Comps.back().isBrackets = false;
     Comps.back().U.IdentInfo = Tok.getIdentifierInfo();
     Comps.back().LocStart = Comps.back().LocEnd = ConsumeToken();
 
-    // FIXME: This loop leaks the index expressions on error.
     while (1) {
       if (Tok.is(tok::period)) {
         // offsetof-member-designator: offsetof-member-designator '.' identifier
         Comps.push_back(Sema::OffsetOfComponent());
         Comps.back().isBrackets = false;
         Comps.back().LocStart = ConsumeToken();
 
         if (Tok.isNot(tok::identifier)) {
while (1) {
         if (Res.isInvalid()) {
           SkipUntil(tok::r_paren, StopAtSemi);
           return Res;
         }
         Comps.back().U.E = Res.get();
 
         ST.consumeClose();
         Comps.back().LocEnd = ST.getCloseLocation();
+      } else if (Tok.is(tok::arrow)) {
+        // offsetof-member-designator: offsetof-member-design '->' identifier
+        // Push array index 0 into offsets.
+        Comps.push_back(Sema::OffsetOfComponent());
+        Comps.back().isBrackets = true;
+        SourceLocation SavedLoc = ConsumeToken();
+        Comps.back().LocStart = Comps.back().LocEnd = SavedLoc;
+        Res = Actions.ActOnIntegerConstant(SourceLocation(), 0);
+        Comps.back().U.E = Res.get();
+
+        Comps.push_back(Sema::OffsetOfComponent());
+        Comps.back().isBrackets = false;
+        Comps.back().LocStart = SavedLoc;
+
+        if (Tok.isNot(tok::identifier)) {
+          Diag(Tok, diag::err_expected) << tok::identifier;
+          SkipUntil(tok::r_paren, StopAtSemi);
+          return ExprError();
+        }
+        Comps.back().U.IdentInfo = Tok.getIdentifierInfo();
+        Comps.back().LocEnd = ConsumeToken();
+
       } else {
         if (Tok.isNot(tok::r_paren)) {
           PT.consumeClose();
           Res = ExprError();
         } else if (Ty.isInvalid()) {
           Res = ExprError();
         } else {
           PT.consumeClose();

clang/test/Parser/offsetof.c

 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
 struct a { struct { int b; } x[2]; };
 
 int a = __builtin_offsetof(struct a, x; // expected-error{{expected ')'}} expected-note{{to match this '('}}
-// FIXME: This actually shouldn't give an error
-int b = __builtin_offsetof(struct a, x->b); // expected-error{{expected ')'}} expected-note{{to match this '('}}