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[C++20] [Modules] Set the feature testing macro to 1 #161034

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Merged
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Sep 29, 2025
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[C++20] [Modules] Set the feature testing macro to 1 #161034

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5 changes: 4 additions & 1 deletion clang/lib/Frontend/InitPreprocessor.cpp
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Expand Up @@ -742,7 +742,10 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
Builder.defineMacro("__cpp_impl_coroutine", "201902L");
Builder.defineMacro("__cpp_designated_initializers", "201707L");
Builder.defineMacro("__cpp_impl_three_way_comparison", "201907L");
//Builder.defineMacro("__cpp_modules", "201907L");
// Intentionally to set __cpp_modules to 1.
// See https://github.com/llvm/llvm-project/issues/71364 for details.
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I am a bit uncomfortable just putting a link w/o at least a TL;DR; giving a high level explanation here.

// Builder.defineMacro("__cpp_modules", "201907L");
Builder.defineMacro("__cpp_modules", "1");
Builder.defineMacro("__cpp_using_enum", "201907L");
}
// C++23 features.
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2 changes: 1 addition & 1 deletion clang/test/Lexer/cxx-features.cpp
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Expand Up @@ -148,7 +148,7 @@

// init_captures checked below

#if check(modules, 0, 0, 0, 0, 0, 0, 0)
#if check(modules, 0, 0, 0, 0, 1, 1, 1)
// FIXME: 201907 in C++20
#error "wrong value for __cpp_modules"
#endif
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