[PATCH] D66919: Warn about zero-parameter K&R definitions in -Wstrict-prototypes

[Aaron Puchert via Phabricator via cfe-commits]

aaronpuchert created this revision.
aaronpuchert added reviewers: arphaman, bruno, rsmith.
Herald added subscribers: cfe-commits, dexonsmith.
Herald added a project: clang.

Zero-parameter K&R definitions specify that the function has no
parameters, but they are still not prototypes, so calling the function
with the wrong number of parameters is just a warning, not an error.

The C11 standard doesn't seem to directly define what a prototype is,
but it can be inferred from 6.9.1p7: "If the declarator includes a
parameter type list, the list also specifies the types of all the
parameters; such a declarator also serves as a function prototype
for later calls to the same function in the same translation unit."
This refers to 6.7.6.3p5: "If, in the declaration “T D1 <https://reviews.llvm.org/D1>”, D1 <https://reviews.llvm.org/D1> has
the form

  D(parameter-type-list)

or

  D(identifier-list_opt)

[...]". Later in 6.11.7 it also refers only to the parameter-type-list
variant as prototype: "The use of function definitions with separate
parameter identifier and declaration lists (not prototype-format
parameter type and identifier declarators) is an obsolescent feature."

We already correctly treat an empty parameter list as non-prototype
declaration, so we can just take that information.

GCC also warns about this with -Wstrict-prototypes.

This shouldn't affect C++, because there all FunctionType's are
FunctionProtoTypes. I added a simple test for that.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66919

Files:
  clang/lib/Sema/SemaDecl.cpp
  clang/test/Sema/warn-strict-prototypes.c
  clang/test/Sema/warn-strict-prototypes.cpp
  clang/test/Sema/warn-strict-prototypes.m


Index: clang/test/Sema/warn-strict-prototypes.m
===================================================================
--- clang/test/Sema/warn-strict-prototypes.m
+++ clang/test/Sema/warn-strict-prototypes.m
@@ -10,7 +10,7 @@
 
 @end
 
-void foo() {
+void foo() { // expected-warning {{this old-style function definition is not preceded by a prototype}}
   void (^block)() = // expected-warning {{this block declaration is not a prototype}}
                     ^void(int arg) { // no warning
   };
Index: clang/test/Sema/warn-strict-prototypes.cpp
===================================================================
--- /dev/null
+++ clang/test/Sema/warn-strict-prototypes.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -verify -fsyntax-only -Wstrict-prototypes %s
+// expected-no-diagnostics
+
+void decl();
+void decl_void(void);
+
+void def() {}
+void def_void(void) {}
Index: clang/test/Sema/warn-strict-prototypes.c
===================================================================
--- clang/test/Sema/warn-strict-prototypes.c
+++ clang/test/Sema/warn-strict-prototypes.c
@@ -7,9 +7,9 @@
 // function declaration with 0 params
 void foo2(void);
 
-// function definition with 0 params(for both cases),
-// valid according to 6.7.5.3/14
-void foo1() {}
+// function definition with 0 params, no prototype.
+void foo1() {} // expected-warning {{this old-style function definition is not preceded by a prototype}}
+// function definition with 0 params, prototype.
 void foo2(void) {}
 
 // function type typedef unspecified params
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -13395,11 +13395,7 @@
       //   Warn if K&R function is defined without a previous declaration.
       //   This warning is issued only if the definition itself does not provide
       //   a prototype. Only K&R definitions do not provide a prototype.
-      //   An empty list in a function declarator that is part of a definition
-      //   of that function specifies that the function has no parameters
-      //   (C99 6.7.5.3p14)
-      if (!FD->hasWrittenPrototype() && FD->getNumParams() > 0 &&
-          !LangOpts.CPlusPlus) {
+      if (!FD->hasWrittenPrototype()) {
         TypeSourceInfo *TI = FD->getTypeSourceInfo();
         TypeLoc TL = TI->getTypeLoc();
         FunctionTypeLoc FTL = TL.getAsAdjusted<FunctionTypeLoc>();


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