When warning about a missing prototype because a function declaration is missing 'void', insert a fixit to add the void.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170399 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -3176,6 +3176,8 @@ def note_sentinel_here : Note<
 def warn_missing_prototype : Warning<
   "no previous prototype for function %0">,
   InGroup<DiagGroup<"missing-prototypes">>, DefaultIgnore;
+def note_declaration_not_a_prototype : Note<
+  "this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function">; 
 def warn_missing_variable_declarations : Warning<
   "no previous extern declaration for non-static variable %0">,
   InGroup<DiagGroup<"missing-variable-declarations">>, DefaultIgnore;

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);

test/Sema/warn-missing-prototypes.c

@@ -1,4 +1,5 @@
-// RUN: %clang -Wmissing-prototypes -fsyntax-only -Xclang -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wdocumentation -Wmissing-prototypes -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wdocumentation -Wmissing-prototypes -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
 int f();
 
@@ -35,3 +36,8 @@ int f2(int x) { return x; }
 
 // rdar://6759522
 int main(void) { return 0; }
+
+void not_a_prototype_test(); // expected-note{{this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function}}
+void not_a_prototype_test() { } // expected-warning{{no previous prototype for function 'not_a_prototype_test'}}
+
+// CHECK: fix-it:"{{.*}}":{40:27-40:27}:"void"