PR41183: Don't emit Wstrict-prototypes warning for an implicit function declaration.

[jyknight]

Summary

This case should emit an -Wimplicit-function-declaration warning.

[jyknight]

Ping.

[jyknight]

Ping.

[rsmith]

LGTM

lib/Sema/SemaType.cpp

if (!LangOpts.CPlusPlus && D.getFunctionDefinitionKind() == FDK_Declaration) {
     bool IsBlock = false;
     for (const DeclaratorChunk &DeclType : D.type_objects()) {
       switch (DeclType.Kind) {
       case DeclaratorChunk::BlockPointer:
         IsBlock = true;
         break;
       case DeclaratorChunk::Function: {
         const DeclaratorChunk::FunctionTypeInfo &FTI = DeclType.Fun;
-        if (FTI.NumParams == 0 && !FTI.isVariadic)
+        // We supress the warning when there's no LParen location, as this
+        // indicates the declaration was an implicit declaration, which gets
+        // warned about separately via -Wimplicit-function-declaration.
+        if (FTI.NumParams == 0 && !FTI.isVariadic && FTI.getLParenLoc().isValid())
           S.Diag(DeclType.Loc, diag::warn_strict_prototypes)
               << IsBlock
               << FixItHint::CreateInsertion(FTI.getRParenLoc(), "void");
         IsBlock = false;
         break;
       }
       default:
         break;

test/Sema/warn-strict-prototypes.c

-// RUN: %clang_cc1 -triple i386-pc-unknown -fsyntax-only -Wstrict-prototypes -verify %s
+// RUN: %clang_cc1 -triple i386-pc-unknown -fsyntax-only -Wstrict-prototypes -Wno-implicit-function-declaration -verify %s
 // RUN: %clang_cc1 -triple i386-pc-unknown -fsyntax-only -Wstrict-prototypes -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
 // function declaration with unspecified params
 void foo1(); // expected-warning {{this function declaration is not a prototype}}
              // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:11-[[@LINE-1]]:11}:"void"
 // function declaration with 0 params
 void foo2(void);
 
void __attribute__((cdecl)) foo12(d) // expected-warning {{this old-style function definition is not preceded by a prototype}}
   short d;
 {}
 
 // No warnings for variadic functions. Overloadable attribute is required
 // to avoid err_ellipsis_first_param error.
 // rdar://problem/33251668
 void foo13(...) __attribute__((overloadable));
 void foo13(...) __attribute__((overloadable)) {}
+
+// We should not generate a strict-prototype warning for an implicit
+// declaration.  Leave that up to the implicit-function-declaration warning.
+void foo14(void) {
+  foo14_call(); // no-warning
+}