[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[Haojian Wu via cfe-commits]

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@@ -1216,10 +1308,225 @@ void DeclareImplicitDeductionGuidesForTypeAlias(
             ->getDeductionCandidateKind() == DeductionCandidate::Aggregate)
       continue;
 
-    BuildDeductionGuideForTypeAlias(SemaRef, AliasTemplate, F, Loc);
+    BuildDeductionGuideForTypeAlias(SemaRef, AliasTemplate, F, Loc,
+                                    DeducingTemplate, DerivedClassMapperType);
   }
 }
 
+void DeclareImplicitDeductionGuidesFromInheritedConstructors(
+    Sema &SemaRef, TemplateDecl *Template, ClassTemplateDecl *Pattern,
+    TypeSourceInfo *BaseTSI, unsigned BaseIdx) {
+  auto &Context = SemaRef.Context;
+  DeclContext *DC = Template->getDeclContext();
+  const auto *BaseTST = BaseTSI->getType()->getAs<TemplateSpecializationType>();
+  if (!BaseTST)
+    return;
+  SourceLocation BaseLoc = BaseTSI->getTypeLoc().getBeginLoc();
+
+  TemplateDecl *BaseTD = BaseTST->getTemplateName().getAsTemplateDecl();
+  if (!BaseTD)
+    return;
+
+  // Subsitute any parameters with default arguments not present in the base,
+  // since partial specializations cannot have default parameters
----------------
hokein wrote:

Can you explain this comment? I'm afraid that I might not completely understand it.

> since partial specializations cannot have default parameters

This is a good point. I think the `partial specialization` here means the the partial specialization of `template <typename> class CC;` which is referred in the standard.

And it is illegal to have default template arguments in a class template partial specialization (in the current implementation, the partial specialization still has the default argument in its template parameters, see my another comment around `PartialSpecTPL`).


https://github.com/llvm/llvm-project/pull/98788