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-Wunused-const-variable incorrectly warns for exported lambda #85122

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davidstone opened this issue Mar 13, 2024 · 2 comments
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-Wunused-const-variable incorrectly warns for exported lambda #85122

davidstone opened this issue Mar 13, 2024 · 2 comments
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@ChuanqiXu9
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clang:diagnostics New/improved warning or error message in Clang, but not in clang-tidy or static analyzer clang:modules C++20 modules and Clang Header Modules false-positive Warning fires when it should not lambda C++11 lambda expressions

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@davidstone
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Compiling the following translation unit with -Wunused-const-variable:

export module a;

export constexpr auto a = []{};

causes clang to report

<source>:3:23: warning: unused variable 'a' [-Wunused-const-variable]
    3 | export constexpr auto a = []{};
      |                       ^
1 warning generated.
Compiler returned: 0

See it live: https://godbolt.org/z/555Y3q9fe

Anything exported from a module should never be considered unused.
@EugeneZelenko EugeneZelenko added clang:diagnostics New/improved warning or error message in Clang, but not in clang-tidy or static analyzer false-positive Warning fires when it should not lambda C++11 lambda expressions and removed new issue labels Mar 13, 2024
@shafik
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shafik commented Mar 13, 2024

CC @ChuanqiXu9

@ChuanqiXu9 ChuanqiXu9 self-assigned this Mar 14, 2024
@tbaederr tbaederr added the clang:modules C++20 modules and Clang Header Modules label Mar 14, 2024
@llvmbot
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llvmbot commented Mar 14, 2024

@llvm/issue-subscribers-clang-modules

Author: David Stone (davidstone)

Compiling the following translation unit with `-Wunused-const-variable`: 
export module a;

export constexpr auto a = []{};

causes clang to report

&lt;source&gt;:3:23: warning: unused variable 'a' [-Wunused-const-variable]
    3 | export constexpr auto a = []{};
      |                       ^
1 warning generated.
Compiler returned: 0

See it live: https://godbolt.org/z/555Y3q9fe

Anything exported from a module should never be considered unused.

tmatheson-arm pushed a commit to tmatheson-arm/llvm-project that referenced this issue Apr 22, 2024
@ChuanqiXu9 @tmatheson-arm
[C++20] [Modules] Mark exported all declarations as used
0ab9676 
Close llvm#85122

As the title suggested, it looks pretty sensible.
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clang:diagnostics New/improved warning or error message in Clang, but not in clang-tidy or static analyzer clang:modules C++20 modules and Clang Header Modules false-positive Warning fires when it should not lambda C++11 lambda expressions
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