| Issue |
135913
|
| Summary |
Incorrect format string determination from manifestly constant-evaluated contexts
|
| Labels |
clang:diagnostics
|
| Assignees |
|
| Reporter |
hubert-reinterpretcast
|
Clang does not observe the surrounding manifestly constant-evaluated context when attempting `-Wformat` diagnostics.
In the case below, the program semantics uses the `"%d\n"` format string.
Clang diagnoses on the basis of the `"%!\n"` string instead.
https://godbolt.org/z/cGsM5Mjn5
### Source (`<stdin>`)
```cpp
#include <stdio.h>
#include <stdarg.h>
constexpr auto const_string() {
if consteval {
return "%d\n";
}
return "%!\n";
}
constexpr auto getvprintf [[gnu::format(__printf__, 1, 0)]](const char *format) {
return [=](va_list vp) {
return vprintf(format, vp);
};
}
constexpr auto myvprintf = getvprintf(const_string());
void q(int x, ...) {
va_list ap;
va_start(ap, x);
myvprintf(ap);
va_end(ap);
}
int main(void) {
q(0, 42);
}
```
### Compiler invocation command
```
clang++ -fsyntax-only -Wall -Wextra -pedantic -std=c++2c -xc++ -
```
### Actual compiler output
```
<stdin>:17:39: warning: invalid conversion specifier '!' [-Wformat-invalid-specifier]
17 | constexpr auto myvprintf = getvprintf(const_string());
| ^~~~~~~~~~~~~~
<stdin>:8:12: note: format string is defined here
8 | return "%!\n";
| ~^
1 warning generated.
```
### Expected compiler output
(No warning)
### Compiler version info (`clang++ -v`)
```
clang version 21.0.0git (https://github.com/llvm/llvm-project.git 77f0708b9d4feee8b8a67a5f571be741be4e26af)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/wandbox/clang-head/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/13
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/14
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/14
Candidate multilib: .;@m64
Selected multilib: .;@m64
```
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