[libc++][cmath] Adding [[nodicard]]
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H-G-Hristov
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[[nodicard]][[nodicard]]
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.htm - https://wg21.link/c.math
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H-G-Hristov
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Dec 16, 2025
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| // Some tests rely on Clang's behaviour of adding `[[gnu::const]]` to the double overload of most of the functions | ||
| // below. Without that attribute being added implicitly, this test can't be checked consistently because its result | ||
| // depends on whether we're getting libc++'s own `std::foo(double)` or the underlying C library's `foo(double)`, e.g. | ||
| // std::fabs(double). | ||
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| // Functions | ||
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| std::fabs(0.F); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}} | ||
| std::fabs(0.); // expected-warning-re 0-1 {{ignoring return value of function declared with {{.*}} attribute}} |
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@frederick-vs-ja @philnik777 I need an advice about the double overloads. Some functions as std::fabs seem to fall into the category as explained in the comment above and produce the respective warning but some don't seem to do that on Clang. I'm not sure how to handle the tests for these overloads (I've added 0-1). Thanks for any advice!
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I'm not convinced we should extend the annotations in cmath for now. The current ones have been added to reflect what Clang diagnoses on its own and I'm hesitant to do anything more, since any functions not annotated currently have side-effects.
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[[nodiscard]]should be applied to functions where discarding the return value is most likely a correctness issue.