sberg added inline comments.
================
Comment at: clang/include/clang/Basic/Attr.td:2996
let Spellings = [GCC<"warn_unused">];
- let Subjects = SubjectList<[Record]>;
+ let Subjects = SubjectList<[Record, CXXConstructor]>;
let Documentation = [Undocumented];
----------------
aaron.ballman wrote:
> I'm confused -- if you want this to behave like `nodiscard`, why aren't these
> changes for `warn_unused_result` (which is what implements `nodiscard`)? I
> don't think this should go on `warn_unused` because that's for the
> declaration of the type as a unit and not written on functions.
>
> I think you don't need any changes to Attr.td for this functionality.
`[[nodiscard]]` and `__attribute__((warn_unused))` already have different
semantics when applied to a class: While both warn about unused expression
results (`-Wunused-value`), only the latter warns about unused variables
(`-Wunused-variable`). This patch keeps that difference, just extends it to
individual constructors:
```
$ cat test.cc
struct [[nodiscard]] S1 {
S1(int) {}
S1(double) {}
};
struct S2 {
[[nodiscard]] S2(int) {}
S2(double) {}
};
struct __attribute__((warn_unused)) S3 {
S3(int) {}
S3(double) {}
};
struct S4 {
__attribute__((warn_unused)) S4(int) {}
S4(double) {}
};
int main() {
S1(0); // expected-warning {{ignoring temporary}}
S1(0.0); // expected-warning {{ignoring temporary}}
S2(0); // expected-warning {{ignoring temporary}}
S2(0.0);
S3(0); // expected-warning {{expression result unused}}
S3(0.0); // expected-warning {{expression result unused}}
S4(0); // expected-warning {{expression result unused}}
S4(0.0);
S1 s1a(0);
S1 s1b(0.0);
S2 s2a(0);
S2 s2b(0.0);
S3 s3a(0); // expected-warning {{unused variable}}
S3 s3b(0.0); // expected-warning {{unused variable}}
S4 s4a(0); // expected-warning {{unused variable}}
S4 s4b(0.0);
}
```
```
$ clang++ -Wunused-value -Wunused-variable -fsyntax-only -Xclang -verify test.cc
```
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D148505/new/
https://reviews.llvm.org/D148505
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