tweak redefinition of a typedef a bit to fix a couple of problems:

1. We had logic in sema to decide whether or not to emit the error
   based on manually checking whether in a system header file.
2. we were allowing redefinitions of typedefs in class scope in C++
   if in header file.
3. there was no way to force typedef redefinitions to be accepted
   by the C compiler, which annoys me when stripping linemarkers out
   of .i files.

The fix is to split the C++ class typedef redefinition path from the
C path, and change the C path to be a warning that normally maps to
error.  This causes it to properly be ignored in system headers, 
etc. and gives us a way to control it.  Passing 
-Wtypedef-redefinition now turns the error into a warning.

One behavior change is that we now diagnose cases where you redefine
a typedef in your .c file that was defined in a header file.  This
seems like reasonable behavior, and the diagnostic now indicates that
it can be controlled with -Wtypedef-redefinition.

llvm-svn: 69391

1 files changed, 12 insertions, 15 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 0fe5715578b..3a264d4449e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -533,25 +533,22 @@ bool Sema::MergeTypeDefDecl(TypedefDecl *New, Decl *OldD) {
   //   In a given non-class scope, a typedef specifier can be used to
   //   redefine the name of any type declared in that scope to refer
   //   to the type to which it already refers.
-  if (getLangOptions().CPlusPlus && !isa<CXXRecordDecl>(CurContext))
-    return false;
-
-  // In C, redeclaration of a type is a constraint violation (6.7.2.3p1).
-  // Apparently GCC, Intel, and Sun all silently ignore the redeclaration if
-  // *either* declaration is in a system header. The code below implements
-  // this adhoc compatibility rule. FIXME: The following code will not
-  // work properly when compiling ".i" files (containing preprocessed output).
-  if (PP.getDiagnostics().getSuppressSystemWarnings()) {
-    SourceManager &SrcMgr = Context.getSourceManager();
-    if (SrcMgr.isInSystemHeader(Old->getLocation()))
-      return false;
-    if (SrcMgr.isInSystemHeader(New->getLocation()))
+  if (getLangOptions().CPlusPlus) {
+    if (!isa<CXXRecordDecl>(CurContext))
       return false;
+    Diag(New->getLocation(), diag::err_redefinition)
+      << New->getDeclName();
+    Diag(Old->getLocation(), diag::note_previous_definition);
+    return true;
   }
 
-  Diag(New->getLocation(), diag::err_redefinition) << New->getDeclName();
+  // If we have a redefinition of a typedef in C, emit a warning.  This warning
+  // is normally mapped to an error, but can be controlled with
+  // -Wtypedef-redefinition.
+  Diag(New->getLocation(), diag::warn_redefinition_of_typedef)
+    << New->getDeclName();
   Diag(Old->getLocation(), diag::note_previous_definition);
-  return true;
+  return false;
 }
 
 /// DeclhasAttr - returns true if decl Declaration already has the target