[AST] Fix -ast-print for _Bool when have diagnostics

For example, given:

  #define bool _Bool
  _Bool i;
  void fn() { 1; }

-ast-print produced:

  tmp.c:3:13: warning: expression result unused
  void fn() { 1; }
              ^
  bool i;
  void fn() {
      1;
  }

That fails to compile because bool is undefined.

Details:

Diagnostics print _Bool as bool when the latter is defined as the
former.  However, diagnostics were altering the printing policy for
-ast-print as well.  The printed source was then invalid because the
preprocessor eats the bool definition.

Problematic diagnostics included suppressed warnings (e.g., add
-Wno-unused-value to the above example), including those that are
suppressed by default.

This patch fixes this bug and cleans up some related comments.

Reviewed by: aaron.ballman, rsmith

Differential Revision: https://reviews.llvm.org/D45093

llvm-svn: 332275

1 files changed, 4 insertions, 3 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index eb336ee8f0f..c0997688b2d 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -52,8 +52,8 @@ ModuleLoader &Sema::getModuleLoader() const { return PP.getModuleLoader(); }
 PrintingPolicy Sema::getPrintingPolicy(const ASTContext &Context,
                                        const Preprocessor &PP) {
   PrintingPolicy Policy = Context.getPrintingPolicy();
-  // Our printing policy is copied over the ASTContext printing policy whenever
-  // a diagnostic is emitted, so recompute it.
+  // In diagnostics, we print _Bool as bool if the latter is defined as the
+  // former.
   Policy.Bool = Context.getLangOpts().Bool;
   if (!Policy.Bool) {
     if (const MacroInfo *BoolMacro = PP.getMacroInfo(Context.getBoolName())) {
@@ -1287,7 +1287,8 @@ void Sema::EmitCurrentDiagnostic(unsigned DiagID) {
     }
   }
 
-  // Set up the context's printing policy based on our current state.
+  // Copy the diagnostic printing policy over the ASTContext printing policy.
+  // TODO: Stop doing that.  See: https://reviews.llvm.org/D45093#1090292
   Context.setPrintingPolicy(getPrintingPolicy());
 
   // Emit the diagnostic.