Let stddef.h respect __need_{wchar_t, size_t, NULL, ptrdiff_t, wint_t}.

glibc expects that stddef.h only defines a single thing if either of these
defines is set.  For example, before this change, a C file containing

  #include <stdlib.h>
  int ptrdiff_t = 0;

would compile with gcc but not with clang. Now it compiles with clang too.

This also fixes PR12997, where older versions of the Linux headers would define
NULL incorrectly, and glibc would define __need_NULL and expect stddef.h to
redefine NULL with the correct definition.

llvm-svn: 207606

2 files changed, 71 insertions, 1 deletions

diff --git a/clang/test/Headers/stddefneeds.cpp b/clang/test/Headers/stddefneeds.cpp
new file mode 100644
index 00000000000..304a224acc6
--- /dev/null
+++ b/clang/test/Headers/stddefneeds.cpp
@@ -0,0 +1,69 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wsentinel -std=c++11 %s
+
+ptrdiff_t p0; // expected-error{{unknown}}
+size_t s0; // expected-error{{unknown}}
+void* v0 = NULL; // expected-error{{undeclared}}
+wint_t w0; // expected-error{{unknown}}
+max_align_t m0; // expected-error{{unknown}}
+
+#define __need_ptrdiff_t
+#include <stddef.h>
+
+ptrdiff_t p1;
+size_t s1; // expected-error{{unknown}}
+void* v1 = NULL; // expected-error{{undeclared}}
+wint_t w1; // expected-error{{unknown}}
+max_align_t m1; // expected-error{{unknown}}
+
+#define __need_size_t
+#include <stddef.h>
+
+ptrdiff_t p2;
+size_t s2;
+void* v2 = NULL; // expected-error{{undeclared}}
+wint_t w2; // expected-error{{unknown}}
+max_align_t m2; // expected-error{{unknown}}
+
+#define __need_NULL
+#include <stddef.h>
+
+ptrdiff_t p3;
+size_t s3;
+void* v3 = NULL;
+wint_t w3; // expected-error{{unknown}}
+max_align_t m3; // expected-error{{unknown}}
+
+// Shouldn't bring in wint_t by default:
+#include <stddef.h>
+
+ptrdiff_t p4;
+size_t s4;
+void* v4 = NULL;
+wint_t w4; // expected-error{{unknown}}
+max_align_t m4;
+
+#define __need_wint_t
+#include <stddef.h>
+
+ptrdiff_t p5;
+size_t s5;
+void* v5 = NULL;
+wint_t w5;
+max_align_t m5;
+
+
+// linux/stddef.h does something like this for cpp files:
+#undef NULL
+#define NULL 0
+
+// glibc (and other) headers then define __need_NULL and rely on stddef.h
+// to redefine NULL to the correct value again.
+#define __need_NULL
+#include <stddef.h>
+
+// gtk headers then use __attribute__((sentinel)), which doesn't work if NULL
+// is 0.
+void f(const char* c, ...) __attribute__((sentinel));
+void g() {
+  f("", NULL);  // Shouldn't warn.
+}
diff --git a/clang/test/Sema/format-strings.c b/clang/test/Sema/format-strings.c
index ad7b37c3e11..e31644a9875 100644
--- a/clang/test/Sema/format-strings.c
+++ b/clang/test/Sema/format-strings.c
@@ -1,8 +1,9 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -Wformat-nonliteral -isystem %S/Inputs %s
 // RUN: %clang_cc1 -fsyntax-only -verify -Wformat-nonliteral -isystem %S/Inputs -fno-signed-char %s
 
-#define __need_wint_t
 #include <stdarg.h>
+#include <stddef.h>
+#define __need_wint_t
 #include <stddef.h> // For wint_t and wchar_t
 
 typedef struct _FILE FILE;