<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/97560>97560</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Typo correction lacks support for much of C
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            c,
            quality-of-implementation,
            clang:diagnostics
      </td>
    </tr>

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

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

<pre>
    If you look at the keywords we add in [`AddKeywordsToConsumer`](https://github.com/llvm/llvm-project/blob/82f9a5ba965dc1a40fe955b8205dd863bf6385cf/clang/lib/Sema/SemaLookup.cpp#L4966), you'll see we are missing quite a few: `_Generic`, `_BitInt`, `_Static_assert`, `_Thread_local`, `nullptr`, `constexpr`, etc are all missing and this shows up in our typo correction behavior: https://godbolt.org/z/9nsKKc4sq

However, it's not a simple matter of adding the keywords to the consumer. Clang supports implicit function declarations in C versions before C23, so `_Genreic(` in an expression context is handled as though the user called an undeclared function rather than an unknown id expression. Similar for `_BitInt` and `_Static_assert`. Further, the typo filter for declaration contexts uses heuristics to determine whether something is a statement or a declaration, and so it doesn't correctly handle `_Thrd_local int i` because the token after the typo `_Thrd_local` is `int` and not an identifier. This means `static _Thrd_local int i` can correct the typo because the leading `static` makes it clear that's a declaration and not a statement, but `_Thrd_local static int i;` cannot correct the typo.
</pre>
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