<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/146429>146429</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] -Wformat size_t issues: suggests `%zf` for "broken" namespaced size_t, doesn't recognize `sizeof(...)`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          rprichard
      </td>
    </tr>
</table>

<pre>
    From https://godbolt.org/z/zssKGfhxW (reduced from https://godbolt.org/z/3G6qjb4KT):

```c++
#include <stdio.h>

namespace foo4 {
    using size_t = unsigned char;
}

namespace foo5 {
    using size_t = float;
}

void test_func(unsigned long s) {
    // Clang suggests replacing %zu with %zu.
    printf("%zu\n", foo4::size_t {});

    // Clang suggests replacing %zu with %zf, a nonsensical specifier
    printf("%u\n", foo5::size_t {});

    // Clang suggests %lu instead of %zu.
    printf("%u\n", sizeof(int));
}
```

Maybe `FormatSpecifier::namedTypeToLengthModifier` ought to ignore a type if it's in a namespace?

Alternatively, it could check whether the typedef refers to the expected integer type.

It might be nice if `sizeof(...)` was regarded as "having size_t type" for the purposes of -Wformat.

</pre>
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