1 files changed, 19 insertions, 2 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 1f80390b402..ab931a773fd 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7762,7 +7762,8 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Declarator &D) {
   return ActOnStartOfFunctionDef(FnBodyScope, DP);
 }
 
-static bool ShouldWarnAboutMissingPrototype(const FunctionDecl *FD) {
+static bool ShouldWarnAboutMissingPrototype(const FunctionDecl *FD, 
+                             const FunctionDecl*& PossibleZeroParamPrototype) {
   // Don't warn about invalid declarations.
   if (FD->isInvalidDecl())
     return false;
@@ -7804,6 +7805,8 @@ static bool ShouldWarnAboutMissingPrototype(const FunctionDecl *FD) {
       continue;
       
     MissingPrototype = !Prev->getType()->isFunctionProtoType();
+    if (FD->getNumParams() == 0)
+      PossibleZeroParamPrototype = Prev;
     break;
   }
     
@@ -7869,8 +7872,22 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Decl *D) {
   //   prototype declaration. This warning is issued even if the
   //   definition itself provides a prototype. The aim is to detect
   //   global functions that fail to be declared in header files.
-  if (ShouldWarnAboutMissingPrototype(FD))
+  const FunctionDecl *PossibleZeroParamPrototype = 0;
+  if (ShouldWarnAboutMissingPrototype(FD, PossibleZeroParamPrototype)) {
     Diag(FD->getLocation(), diag::warn_missing_prototype) << FD;
+  
+    if (PossibleZeroParamPrototype) {
+      // We found a declaration that is not a prototype, 
+      // but that could be a zero-parameter prototype
+      TypeSourceInfo* TI = PossibleZeroParamPrototype->getTypeSourceInfo();
+      TypeLoc TL = TI->getTypeLoc();
+      if (FunctionNoProtoTypeLoc* FTL = dyn_cast<FunctionNoProtoTypeLoc>(&TL))
+        Diag(PossibleZeroParamPrototype->getLocation(), 
+             diag::note_declaration_not_a_prototype)
+          << PossibleZeroParamPrototype 
+          << FixItHint::CreateInsertion(FTL->getRParenLoc(), "void");
+    }
+  }
 
   if (FnBodyScope)
     PushDeclContext(FnBodyScope, FD);