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

[Haojian Wu via cfe-commits]

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@@ -2612,44 +2669,312 @@ struct ConvertConstructorToDeductionGuideTransform {
     SemaRef.CurrentInstantiationScope->InstantiatedLocal(OldParam, NewParam);
     return NewParam;
   }
+};
 
-  FunctionTemplateDecl *buildDeductionGuide(
-      TemplateParameterList *TemplateParams, CXXConstructorDecl *Ctor,
-      ExplicitSpecifier ES, TypeSourceInfo *TInfo, SourceLocation LocStart,
-      SourceLocation Loc, SourceLocation LocEnd,
-      llvm::ArrayRef<TypedefNameDecl *> MaterializedTypedefs = {}) {
-    DeclarationNameInfo Name(DeductionGuideName, Loc);
-    ArrayRef<ParmVarDecl *> Params =
-        TInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams();
+// Find all template parameters that appear in the given DeducedArgs.
+// Return the indices of the template parameters in the TemplateParams.
+SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
+    ArrayRef<NamedDecl *> TemplateParams,
+    ArrayRef<TemplateArgument> DeducedArgs) {
+  struct FindAppearedTemplateParams
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hokein wrote:

OK, I'm not sure `Type` is the best fit, I'd stay close with template params.  Renamed it to `TemplateParamsReferencedFinder` (if we want to use a less-verbose name, I'm fine with `Finder` since this is a structure defined in a function body).

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