[Clang] Missing deduction error diagnostic in C when array size is different

[to268]

Since type inference was implemented in Clang for C23, it appears that we do not check if there is a mismatch between the declared type and the deduced type in C, as we do in C++.

For example: auto s[3] = "abc" is deduced as char[4] and therefore should not be compatible with char[3], but we do not enforce this check in C mode and end up with char[4] instead of bailing out with char[3] != char[4].

Godbolt C example
Godbolt C++ example

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Guillot Tony (to268)

Since [type inference](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3007.htm) was implemented in Clang for C23, it appears that we do not check if there is a mismatch between the declared type and the deduced type in C, as we do in C++.

For example: auto s[3] = "abc" is deduced as char[4] and therefore should not be compatible with char[3], but we do not enforce this check in C mode and end up with char[4] instead of bailing out with char[3] != char[4].

Godbolt C example
Godbolt C++ example