[clang] [clang-tools-extra] [clang] Implement CWG2398 provisional TTP matching to class templates (PR #94981)

[Matheus Izvekov via cfe-commits]

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@@ -1371,11 +1371,17 @@ class TemplateDiff {
   /// argument info into a tree.
   void DiffTemplate(const TemplateSpecializationType *FromTST,
                     const TemplateSpecializationType *ToTST) {
+    // FIXME: With P3310R0, A TST formed from a DeducedTemplateName might
+    // differ in template arguments which were not written.
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mizvekov wrote:

It's still possible these types might appear in diagnostics, even if they don't make it to the final program.

https://github.com/llvm/llvm-project/pull/94981