[clang-tidy] modernize-use-using suggested for extern "C" typedefs

[LegalizeAdulthood]

Repro: https://godbolt.org/z/6jdqMrjKs

The following code:

extern "C"
{
typedef int int_t;
}

should not issue any warnings with modernize-use-using because the typedef is inside an extern "C" block.

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Richard Thomson (LegalizeAdulthood)

Repro: https://godbolt.org/z/6jdqMrjKs

The following code:

extern "C"
{
typedef int int_t;
}

should not issue any warnings with modernize-use-using because the typedef is inside an extern "C" block.

[LegalizeAdulthood]

This is common inside headers that are declaring a C API (and therefore use typedef) which is to be available for C or C++ clients.

[frederick-vs-ja]

IIUC the example is still putting the typedef declaration in .cpp source file. Can we show an example where the typedef declaration is put into a header (available in both C and C++) and the header is included by a C++ source file?

[vbvictor]

modernize-use-using has an option IgnoreExternC, does it cover all your cases? https://godbolt.org/z/G876fbKda