[clang] [libcxx] [Clang] Implement CWG2369 "Ordering between constraints and substitution" (PR #102857)

[Matheus Izvekov via cfe-commits]

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@@ -13051,11 +13051,14 @@ class Sema final : public SemaBase {
   /// instantiation arguments.
   ///
   /// \param DC In the event we don't HAVE a declaration yet, we instead provide
-  ///  the decl context where it will be created.  In this case, the `Innermost`
-  ///  should likely be provided.  If ND is non-null, this is ignored.
+  ///  the decl context where it will be created.  In this case, the \p
+  ///  Innermost should likely be provided.  If \p ND is non-null and \p
+  ///  Innermost is NULL, this is ignored.
   ///
   /// \param Innermost if non-NULL, specifies a template argument list for the
-  /// template declaration passed as ND.
+  /// template declaration passed as \p ND. The next declaration context would
+  /// be switched to \p DC if present; otherwise, it would be the semantic
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mizvekov wrote:

It means the visitation order. In order to collect the instantiation arguments, we start with a declaration and walk up toward its template parents. This function could use a refactor and be smarter in figuring out how to walk up from ND alone, so that the DC parameter becomes unnecessary and could be removed.

https://github.com/llvm/llvm-project/pull/102857