[clang] [Clang] Improve diagnostics to show the correct position for `[[maybe_unused]]` before a using-alias (PR #223910)

[Younan Zhang via cfe-commits]

================
@@ -469,382 +753,400 @@ features cannot lower the translation-unit ABI level;
   against or converted to a null pointer, the same as a bare function name.
   (#GH46362)
 
-- Clang now attempts to print enumerator names rather than C-style cast expressions
-  in more diagnostics.
-
-- `-Wunsafe-buffer-usage` now warns about unsafe two-parameter constructors of
-  `std::string_view` (pointer and size), consistent with the existing warning for `std::span`.
-
-- `-Wno-unsafe-buffer-usage-in-static-sized-array` now also suppresses warnings
-  for pointer arithmetic on statically-sized arrays when the offset is a
-  non-negative constant within the array bounds.
-
-- `-Wc++98-compat` now diagnoses explicit conversion functions in C++20 and
-  later, matching the behavior in C++11 through C++17. (#GH161689)
+- Added a clearer diagnostic for uninitialized decomposition declarations. (#GH90107)
 
-- Added `-Wcounter-extension` as a diagnostic group under `-Wc2y-extensions` to
-  control `__COUNTER__` being diagnosed as an extension. This allows `-pedantic`
-  users to disable the diagnostic with `-Wno-counter-extension` without having
-  to disable all pedantic diagnostics. (#GH196557)
+- Fixed missing sentinel attribute diagnostic discrepancy with explicit object
+  parameters in variadic functions. (#GH200007)
 
-- Clang now diagnoses more details when a constraint evaluates to false.
-
-- `-Wpointer-arith` no longer reports subtraction of pointers to a variably
-  modified type, such as `int[n]`, as a subtraction of pointers to a type of
-  zero size, unless the size is provably zero: a zero-sized base element or a
-  dimension that is a zero integer constant, as in `struct Empty vla[n]` or
-  `int vla[n][0]`. (#GH28328)
-
-- Fixed a missing `-Wconstant-conversion` diagnostic for signed `char` arrays.
-
-- Clang now diagnoses passing wrong vector type as a mask to `__builtin_shufflevector`. (#GH218132)
-
-- `-Wdelete-abstract-non-virtual-dtor` and `-Wdelete-non-abstract-non-virtual-dtor`
-  no longer warn when the selected deallocation function is a destroying
-  `operator delete`, since such a delete expression never invokes the
-  destructor. (#GH65524)
-
-- Fixed a false-positive `-Wshadow` warning when a variable in an
-  inline-defined friend function shares the name of a non-static class
-  member variable. (#GH221190)
-
-- Clang now diagnoses matrix logical operations are only supported for HLSL. (GH222381)
+- Suggests the correct location for an attribute written before the `using`
+  keyword of an alias-declaration, with a fix-it, e.g. for
+  `[[maybe_unused]] using T = int;`.
----------------
zyn0217 wrote:

```suggestion
- Suggests the correct location for an attribute written before the `using`
  keyword of an alias-declaration. (#GH155787)
```

https://github.com/llvm/llvm-project/pull/223910