https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113051
Bug ID: 113051
Summary: -Wformat-signedness wrongly triggers for values from
template arguments
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: adam.f.badura at gmail dot com
Target Milestone: ---
Consider sample code (https://godbolt.org/z/7T3vGefEq):
```
#include <cinttypes>
#include <cstdio>
template<std::uint8_t i>
auto foo()
{
return std::printf("%u\n", i);
}
auto bar(std::uint8_t i)
{
return std::printf("%u\n", i);
}
void test()
{
foo<11>();
bar(11);
}
```
When compiled with
```
-std=c++17 -Wformat=1 -Wformat-signedness
```
on GCC 10.2 (where I detected it) and GCC trunk (as on Compiler Explorer from
the link) I'm getting the following warning:
```
<source>: In instantiation of 'auto foo() [with unsigned char i = 11]':
<source>:17:10: required from here
17 | foo<11>();
| ~~~~~~~^~
<source>:7:24: warning: format '%u' expects argument of type 'unsigned int',
but argument 2 has type 'int' [-Wformat=]
7 | return std::printf("%u\n", i);
| ~^
| |
| unsigned int
| %u
```
The warning is not reported in `bar` but is reported in `foo` where the
argument comes from the template.
As an attempt to work around the problem I have tried to explicitly force the
type of `i` in `foo` to `std::uint8_t` (https://godbolt.org/z/eK5TTx93o) and
`std::uint16_t` (https://godbolt.org/z/rqY6n58n8), but it didn't help. Only
forcing `std::uint32_t` helped (https://godbolt.org/z/j7MY7YTeG).
