[clang] [clang] Implement CTAD for type alias template. (PR #77890)

[Haojian Wu via cfe-commits]

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@@ -10636,6 +10889,113 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
   // clear on this, but they're not found by name so access does not apply.
   Guides.suppressDiagnostics();
 
+  SmallVector<DeclAccessPair> GuidesCandidates;
+  if (AliasTemplate) {
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hokein wrote:

Yes, and this is not the proper place to construct deduction guides for alias templates (they should live in `DeclareImplicitDeductionGuides`).

https://github.com/llvm/llvm-project/pull/77890