Fix the declaration printer to properly handle prototypes in C

Previously, we would take a declaration like void f(void) and print it
as void f(). That's correct in C++ as far as it goes, but is incorrect
in C because that converts the function from having a prototype to one
which does not.

This turns out to matter for some of our tests that use the pretty
printer where we'd like to get rid of the K&R prototypes from the test
but can't because the test is checking the pretty printed function
signature, as done with the ARCMT tests.

clang/lib/AST/DeclPrinter.cpp

@@ -680,6 +680,10 @@ void DeclPrinter::VisitFunctionDecl(FunctionDecl *D) {
       if (FT->isVariadic()) {
         if (D->getNumParams()) POut << ", ";
         POut << "...";
+      } else if (!D->getNumParams() && !Context.getLangOpts().CPlusPlus) {
+        // The function has a prototype, so it needs to retain the prototype
+        // in C.
+        POut << "void";
       }
     } else if (D->doesThisDeclarationHaveABody() && !D->hasPrototype()) {
       for (unsigned i = 0, e = D->getNumParams(); i != e; ++i) {

clang/test/Analysis/cfg.c

@@ -40,7 +40,7 @@ void checkWrap(int i) {
   }
 }
 
-// CHECK-LABEL: void checkGCCAsmRValueOutput()
+// CHECK-LABEL: void checkGCCAsmRValueOutput(void)
 // CHECK: [B2 (ENTRY)]
 // CHECK-NEXT: Succs (1): B1
 // CHECK: [B1]

clang/test/Analysis/designated-initializer.c

@@ -16,7 +16,7 @@ void test(void) {
   }; 
 }
 
-// CHECK: void test()
+// CHECK: void test(void)
 // CHECK: [B1]
 // CHECK:   1: getUQ
 // CHECK:   2: [B1.1] (ImplicitCastExpr, FunctionToPointerDecay, union UQ (*)(void))

clang/test/Analysis/std-c-library-functions-vs-stream-checker.c

@@ -28,7 +28,7 @@
 
 // Verify that the summaries are loaded when the StdLibraryFunctionsChecker is
 // enabled.
-//      CHECK: Loaded summary for: int getchar()
+//      CHECK: Loaded summary for: int getchar(void)
 // CHECK-NEXT: Loaded summary for: unsigned long fread(void *restrict, size_t, size_t, FILE *restrict)
 // CHECK-NEXT: Loaded summary for: unsigned long fwrite(const void *restrict, size_t, size_t, FILE *restrict)
 

clang/test/Analysis/std-c-library-functions.c

@@ -52,7 +52,7 @@
 // CHECK-NEXT: Loaded summary for: int isxdigit(int)
 // CHECK-NEXT: Loaded summary for: int getc(FILE *)
 // CHECK-NEXT: Loaded summary for: int fgetc(FILE *)
-// CHECK-NEXT: Loaded summary for: int getchar()
+// CHECK-NEXT: Loaded summary for: int getchar(void)
 // CHECK-NEXT: Loaded summary for: unsigned int fread(void *restrict, size_t, size_t, FILE *restrict)
 // CHECK-NEXT: Loaded summary for: unsigned int fwrite(const void *restrict, size_t, size_t, FILE *restrict)
 // CHECK-NEXT: Loaded summary for: ssize_t read(int, void *, size_t)

clang/test/OpenMP/declare_mapper_ast_print.c

@@ -41,7 +41,7 @@ struct dat {
 #pragma omp declare mapper(struct dat d) map(to: d.d)
 // CHECK: #pragma omp declare mapper (default : struct dat d) map(to: d.d){{$}}
 
-// CHECK: int main() {
+// CHECK: int main(void) {
 int main(void) {
 #pragma omp declare mapper(id: struct vec v) map(v.len)
 // CHECK: #pragma omp declare mapper (id : struct vec v) map(tofrom: v.len)

clang/test/OpenMP/declare_reduction_ast_print.c

@@ -31,7 +31,7 @@ void init(struct SSS *priv, struct SSS orig);
 #pragma omp declare reduction(fun : struct SSS : omp_out = omp_in) initializer(init(&omp_priv, omp_orig))
 // CHECK: #pragma omp declare reduction (fun : struct SSS : omp_out = omp_in) initializer(init(&omp_priv, omp_orig))
 
-// CHECK: int main() {
+// CHECK: int main(void) {
 int main(void) {
 #pragma omp declare reduction(fun : struct SSS : omp_out = omp_in) initializer(init(&omp_priv, omp_orig))
   // CHECK: #pragma omp declare reduction (fun : struct SSS : omp_out = omp_in) initializer(init(&omp_priv, omp_orig))

clang/test/OpenMP/declare_variant_ast_print.c

@@ -25,7 +25,7 @@ int foo(void);
 #pragma omp declare variant(foo) match(implementation={extension(match_none)})
 int bar(void);
 
-// CHECK:      int foo();
+// CHECK:      int foo(void);
 // CHECK-NEXT: #pragma omp declare variant(foo) match(implementation={extension(match_none)})
 // CHECK-NEXT: #pragma omp declare variant(foo) match(implementation={extension(match_any)})
 // CHECK-NEXT: #pragma omp declare variant(foo) match(implementation={extension(match_all)})
@@ -41,4 +41,4 @@ int bar(void);
 // CHECK-NEXT: #pragma omp declare variant(foo) match(construct={parallel})
 // CHECK-NEXT: #pragma omp declare variant(foo) match(construct={teams})
 // CHECK-NEXT: #pragma omp declare variant(foo) match(construct={target})
-// CHECK-NEXT: int bar();
+// CHECK-NEXT: int bar(void);

clang/test/OpenMP/metadirective_ast_print.c

@@ -59,8 +59,8 @@ void foo(void) {
   }
 }
 
-// CHECK: void bar();
-// CHECK: void foo()
+// CHECK: void bar(void);
+// CHECK: void foo(void)
 // CHECK-NEXT: #pragma omp parallel
 // CHECK-NEXT: bar()
 // CHECK-NEXT: #pragma omp parallel

clang/test/PCH/chain-decls.c

@@ -9,8 +9,8 @@
 
 // expected-no-diagnostics
 
-// CHECK: void f();
-// CHECK: void g();
+// CHECK: void f(void);
+// CHECK: void g(void);
 
 int h(void) {
   f();

clang/test/PCH/chain-macro.c

@@ -4,7 +4,7 @@
 // RUN: %clang_cc1 -ast-print -include-pch %t2 %s | FileCheck %s
 // expected-no-diagnostics
 
-// CHECK: void f();
+// CHECK: void f(void);
 FOOBAR
-// CHECK: void g();
+// CHECK: void g(void);
 BARFOO

clang/test/Sema/attr-print.c

@@ -10,11 +10,10 @@ __declspec(align(4)) int y;
 // CHECK: short arr[3] __attribute__((aligned));
 short arr[3] __attribute__((aligned));
 
-// FIXME: -ast-print is printing this function signature with a K&R C style.
-// CHECK: void foo() __attribute__((const));
+// CHECK: void foo(void) __attribute__((const));
 void foo(void) __attribute__((const));
 
-// CHECK: void bar() __attribute__((__const));
+// CHECK: void bar(void) __attribute__((__const));
 void bar(void) __attribute__((__const));
 
 // CHECK: int * __ptr32 p32;

clang/test/SemaObjC/static-ivar-ref-1.m

@@ -24,7 +24,7 @@ int foo(void)
 // CHECK: }
 // CHECK: @end
 // CHECK: current *pc;
-// CHECK: int foo() {
+// CHECK: int foo(void) {
 // CHECK:     return pc->ivar2 + (*pc).ivar + pc->ivar1;
 // CHECK: }