3 files changed, 105 insertions, 5 deletions

diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index 97126ed1527..2dfe0a29b2a 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -23,9 +23,22 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef __STDDEF_H
+#if !defined(__STDDEF_H) || defined(__need_ptrdiff_t) ||                       \
+    defined(__need_size_t) || defined(__need_wchar_t) ||                       \
+    defined(__need_NULL) || defined(__need_wint_t)
+
+#if !defined(__need_ptrdiff_t) && !defined(__need_size_t) &&                   \
+    !defined(__need_wchar_t) && !defined(__need_NULL) &&                       \
+    !defined(__need_wint_t)
 #define __STDDEF_H
+#define __need_ptrdiff_t
+#define __need_size_t
+#define __need_wchar_t
+#define __need_NULL
+/* __need_wint_t is intentionally not defined here. */
+#endif
 
+#if defined(__need_ptrdiff_t)
 #if !defined(_PTRDIFF_T) || __has_feature(modules)
 /* Always define ptrdiff_t when modules are available. */
 #if !__has_feature(modules)
@@ -33,7 +46,10 @@
 #endif
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
 #endif
+#undef __need_ptrdiff_t
+#endif /* defined(__need_ptrdiff_t) */
 
+#if defined(__need_size_t)
 #if !defined(_SIZE_T) || __has_feature(modules)
 /* Always define size_t when modules are available. */
 #if !__has_feature(modules)
@@ -41,7 +57,10 @@ typedef __PTRDIFF_TYPE__ ptrdiff_t;
 #endif
 typedef __SIZE_TYPE__ size_t;
 #endif
+#undef __need_size_t
+#endif /*defined(__need_size_t) */
 
+#if defined(__STDDEF_H)
 /* ISO9899:2011 7.20 (C11 Annex K): Define rsize_t if __STDC_WANT_LIB_EXT1__ is
  * enabled. */
 #if (defined(__STDC_WANT_LIB_EXT1__) && __STDC_WANT_LIB_EXT1__ >= 1 && \
@@ -52,7 +71,9 @@ typedef __SIZE_TYPE__ size_t;
 #endif
 typedef __SIZE_TYPE__ rsize_t;
 #endif
+#endif /* defined(__STDDEF_H) */
 
+#if defined(__need_wchar_t)
 #ifndef __cplusplus
 /* Always define wchar_t when modules are available. */
 #if !defined(_WCHAR_T) || __has_feature(modules)
@@ -65,7 +86,10 @@ typedef __SIZE_TYPE__ rsize_t;
 typedef __WCHAR_TYPE__ wchar_t;
 #endif
 #endif
+#undef __need_wchar_t
+#endif /* defined(__need_wchar_t) */
 
+#if defined(__need_NULL)
 #undef NULL
 #ifdef __cplusplus
 #  if !defined(__MINGW32__) && !defined(_MSC_VER)
@@ -76,15 +100,19 @@ typedef __WCHAR_TYPE__ wchar_t;
 #else
 #  define NULL ((void*)0)
 #endif
-
 #ifdef __cplusplus
 #if defined(_MSC_EXTENSIONS) && defined(_NATIVE_NULLPTR_SUPPORTED)
 namespace std { typedef decltype(nullptr) nullptr_t; }
 using ::std::nullptr_t;
 #endif
 #endif
+#undef __need_NULL
+#endif /* defined(__need_NULL) */
+
+#if defined(__STDDEF_H)
 
 #if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) || __has_feature(modules)
 #ifndef _MSC_VER
 typedef struct {
   long long __clang_max_align_nonce1
@@ -97,10 +125,10 @@ typedef double max_align_t;
 #endif
 #define __CLANG_MAX_ALIGN_T_DEFINED
 #endif
+#endif
 
 #define offsetof(t, d) __builtin_offsetof(t, d)
-
-#endif /* __STDDEF_H */
+#endif  /* __STDDEF_H */
 
 /* Some C libraries expect to see a wint_t here. Others (notably MinGW) will use
 __WINT_TYPE__ directly; accommodate both by requiring __need_wint_t */
@@ -114,3 +142,5 @@ typedef __WINT_TYPE__ wint_t;
 #endif
 #undef __need_wint_t
 #endif /* __need_wint_t */
+
+#endif
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;