<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/60866>60866</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang-format] QualifierOrder should support All of C++'s declaration specifiers.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    Clang format supports a limited number of [C++'s *decl-specifier*s (and children)](https://eel.is/c++draft/dcl.spec.general) in its [QualifierOrder](https://github.com/llvm/llvm-project/blob/main/clang/docs/ClangFormatStyleOptions.rst#id231) option. It should support all of them and, optionally, alias the ones which are similar to each other when not explicitly included in QualifierOrder.

Here's a list of qualifiers that could be added:
- typedef
- consteval
- constinit
- thread_local
- extern
- mutable
- signed
- unsigned
- long
- short
- decltype
- auto

Sticking the aliasing behind a new flag will keep backwards compatibility, or forgo it completely and require each qualifier be included if the user wants to reorder it (e.g. "static, extern, mutable, thread_local, constexpr, constinit, consteval, signed, unsigned, short, long, type, decltype, auto").

The way I envision the aliasing working is:
```cpp
// With a QualifierOrder: "inline, constexpr, static, type"

// Current behavior:
int inline static consteval long example0();
// becomes (`consteval` is unrecognized)
inline static int consteval long example0();

// New proposed behavior:
// `consteval` and `constinit` will be treated as `constexpr`
// `mutable`, `extern`, and `thread_local` will be treated as `static`
//   Note: `extern "C"` and `extern "C++"` are linkage-specifications 
//   and can't be freely reordered in a decl-specifier-seq
// `decltype` and `auto` will be treated as `type`
static inline decltype(12) constinit example1 = 12;
// becomes
inline constinit static decltype(12) example1 = 12;


// With a QualifierOrder: "static, const, type"

// Current behavior:
int static volatile const example2;
// becomes (it gives up if a qualifier that isn't in QualifierOrder is encountered)
static int volatile const example2;

// New proposed behavior:
// `volatile` will be treated as `const` if not in QualifierOrder
int volatile const example3;
// becomes
const volatile int example3;


// With a QualifierOrder: "short, signed, type"

// New proposed behavior:
// `short` and `long` can match to each other before `type`.
// `signed` and `unsigned` can match to each other before `type`.
unsigned long int long example4;
// becomes
long long unsigned int example4;


// With a QualifierOrder: "thread_local, signed, short, type, static, long"

// New proposed behavior:
// if a qualifier and its alias are both present, prefer the place it's explicitly named.
extern thread_local unsigned long example5;
// becomes
thread_local unsigned extern long example5;
``` 
</pre>
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