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[clang][headers] Including stddef.h always redefines NULL (#99727)
stddef.h always includes __stddef_null.h. This is fine in modules because it's not possible to re-include the pcm, and it's necessary to export the _Builtin_stddef.null submodule. However, without modules it causes NULL to always get redefined which disrupts some C++ code. Rework the inclusion of __stddef_null.h so that with not building with modules it's only included if __need_NULL is set by the includer, or it's the first time stddef.h is being included. (cherry picked from commit 92a9d48)
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| Original file line number | Diff line number | Diff line change |
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| // RUN: rm -rf %t | ||
| // RUN: split-file %s %t | ||
| // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/no-lsv -I%t %t/stddef.cpp -verify | ||
| // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-local-submodule-visibility -fmodules-cache-path=%t/lsv -I%t %t/stddef.cpp -verify | ||
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| //--- stddef.cpp | ||
| #include <b.h> | ||
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| void *pointer = NULL; | ||
| size_t size = 0; | ||
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| // When building with modules, a pcm is never re-imported, so re-including | ||
| // stddef.h will not re-import _Builtin_stddef.null to restore the definition of | ||
| // NULL, even though stddef.h will unconditionally include __stddef_null.h when | ||
| // building with modules. | ||
| #undef NULL | ||
| #include <stddef.h> | ||
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| void *anotherPointer = NULL; // expected-error{{use of undeclared identifier 'NULL'}} | ||
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| // stddef.h needs to be a `textual` header to support clients doing things like | ||
| // this. | ||
| // | ||
| // #define __need_NULL | ||
| // #include <stddef.h> | ||
| // | ||
| // As a textual header designed to be included multiple times, it can't directly | ||
| // declare anything, or those declarations would go into every module that | ||
| // included it. e.g. if stddef.h contained all of its declarations, and modules | ||
| // A and B included stddef.h, they would both have the declaration for size_t. | ||
| // That breaks Swift, which uses the module name as part of the type name, i.e. | ||
| // A.size_t and B.size_t are treated as completely different types in Swift and | ||
| // cannot be interchanged. To fix that, stddef.h (and stdarg.h) are split out | ||
| // into a separate file per __need macro that can be normal headers in explicit | ||
| // submodules. That runs into yet another wrinkle though. When modules build, | ||
| // declarations from previous submodules leak into subsequent ones when not | ||
| // using local submodule visibility. Consider if stddef.h did the normal thing. | ||
| // | ||
| // #ifndef __STDDEF_H | ||
| // #define __STDDEF_H | ||
| // // include all of the sub-headers | ||
| // #endif | ||
| // | ||
| // When SM builds without local submodule visibility, it will precompile a.h | ||
| // first. When it gets to b.h, the __STDDEF_H declaration from precompiling a.h | ||
| // will leak, and so when b.h includes stddef.h, it won't include any of its | ||
| // sub-headers, and SM.B will thus not import _Builtin_stddef or make any of its | ||
| // submodules visible. Precompiling b.h will be fine since it sees all of the | ||
| // declarations from a.h including stddef.h, but clients that only include b.h | ||
| // will not see any of the stddef.h types. stddef.h thus has to make sure to | ||
| // always include the necessary sub-headers, even if they've been included | ||
| // already. They all have their own header guards to allow this. | ||
| // __stddef_null.h is extra special, so this test makes sure to cover NULL plus | ||
| // one of the normal stddef.h types. | ||
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| //--- module.modulemap | ||
| module SM { | ||
| module A { | ||
| header "a.h" | ||
| export * | ||
| } | ||
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| module B { | ||
| header "b.h" | ||
| export * | ||
| } | ||
| } | ||
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| //--- a.h | ||
| #include <stddef.h> | ||
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| //--- b.h | ||
| #include <stddef.h> |