[libcxx-commits] [libcxx] [libc++] stddef.h needs to #include_next for the new clang __need_ macros (PR #86252)

[Ian Anderson via libcxx-commits]

================
@@ -0,0 +1,185 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// This is the same test as clang/test/Headers/stddefneeds.c, but to test the
+// libc++ version of stddef.h interacts properly with the clang version.
+
+struct astruct {
+  char member;
+};
+
+ptrdiff_t p0;                           // expected-error{{unknown type name 'ptrdiff_t'}}
+size_t s0;                              // expected-error{{unknown type name 'size_t'}}
+rsize_t r0;                             // expected-error{{unknown type name 'rsize_t'}}
+wchar_t wc0;                            // wchar_t is a keyword in C++
+void* v0 = NULL;                        // expected-error{{use of undeclared identifier 'NULL'}}
+nullptr_t n0;                           // expected-error{{unknown type name 'nullptr_t'}}
+static void f0(void) { unreachable(); } // expected-error{{undeclared identifier 'unreachable'}}
+max_align_t m0;                         // expected-error{{unknown type name 'max_align_t'}}
+size_t o0 = offsetof(
+    struct astruct,
+    member); // expected-error{{unknown type name 'size_t'}} expected-error{{expected expression}} expected-error{{use of undeclared identifier 'member'}}
+wint_t wi0;  // expected-error{{unknown type name 'wint_t'}}
+
+#define __need_ptrdiff_t
+#include <stddef.h>
+
+ptrdiff_t p1;
+size_t s1;  // expected-error{{unknown type}}
+rsize_t r1; // expected-error{{unknown type}}
+wchar_t wc1;
+void* v1 = NULL;                        // expected-error{{undeclared identifier}}
+nullptr_t n1;                           // expected-error{{unknown type}}
+static void f1(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m1;                         // expected-error{{unknown type}}
+size_t o1 = offsetof(
+    struct astruct,
+    member); // expected-error{{unknown type}} expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi1; // expected-error{{unknown type}}
+
+// The "must be declared before used" errors are only emitted the first time a
+// known-but-not-visible type is seen. At this point the _Builtin_stddef module
+// has been built and all of the types tried, so most of the errors won't be
+// repeated below in modules. The types still aren't available, just the errors
+// aren't repeated. e.g. rsize_t still isn't available, if r1 above got deleted,
+// its error would move to r2 below.
+
+#define __need_size_t
+#include <stddef.h>
+
+ptrdiff_t p2;
+size_t s2;
+rsize_t r2; // expected-error{{unknown type}}
+wchar_t wc2;
+void* v2 = NULL;                        // expected-error{{undeclared identifier}}
+nullptr_t n2;                           // expected-error{{unknown type}}
+static void f2(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m2;                         // expected-error{{unknown type}}
+size_t o2 =
+    offsetof(struct astruct, member); // expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi2;                           // expected-error{{unknown type}}
+
+#define __need_rsize_t
+#include <stddef.h>
+
+ptrdiff_t p3;
+size_t s3;
+rsize_t r3;
+wchar_t wc3;
+void* v3 = NULL;                        // expected-error{{undeclared identifier}}
+nullptr_t n3;                           // expected-error{{unknown type}}
+static void f3(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m3;                         // expected-error{{unknown type}}
+size_t o3 =
+    offsetof(struct astruct, member); // expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi3;                           // expected-error{{unknown type}}
+
+#define __need_wchar_t
+#include <stddef.h>
+
+ptrdiff_t p4;
+size_t s4;
+rsize_t r4;
+wchar_t wc4;
+void* v4 = NULL;                        // expected-error{{undeclared identifier}}
+nullptr_t n4;                           // expected-error{{unknown type}}
+static void f4(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m4;                         // expected-error{{unknown type}}
+size_t o4 =
+    offsetof(struct astruct, member); // expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi4;                           // expected-error{{unknown type}}
+
+#define __need_NULL
+#include <stddef.h>
+
+ptrdiff_t p5;
+size_t s5;
+rsize_t r5;
+wchar_t wc5;
+void* v5 = NULL;
+nullptr_t n5;                           // expected-error{{unknown type}}
+static void f5(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m5;                         // expected-error{{unknown type}}
+size_t o5 =
+    offsetof(struct astruct, member); // expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi5;                           // expected-error{{unknown type}}
+
+// nullptr_t doesn't get declared before C23 because its definition
+// depends on nullptr.
+#define __need_nullptr_t
+#include <stddef.h>
+
+ptrdiff_t p6;
+size_t s6;
+rsize_t r6;
+wchar_t wc6;
+void* v6 = NULL;
+nullptr_t n6;
+static void f6(void) { unreachable(); } // expected-error{{undeclared identifier}}
+max_align_t m6;                         // expected-error{{unknown type}}
+size_t o6 =
+    offsetof(struct astruct, member); // expected-error{{expected expression}} expected-error{{undeclared identifier}}
+wint_t wi6;                           // expected-error{{unknown type}}
+
+#define __need_unreachable
+#include <stddef.h>
+
+ptrdiff_t p7;
+size_t s7;
+rsize_t r7;
+wchar_t wc7;
+void* v7 = NULL;
+nullptr_t n7;
+static void f7(void) { unreachable(); }
----------------
ian-twilightcoder wrote:

Should this be allowed? Should the clang version of stddef.h never declare the `unreachable` macro even if `__need_unreachable` is set? `__need_unreachable` is new in LLVM 18.

https://github.com/llvm/llvm-project/pull/86252