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

[via cfe-commits]

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@@ -980,19 +986,69 @@ getRHSTemplateDeclAndArgs(Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate) {
   return {Template, AliasRhsTemplateArgs};
 }
 
+// Build the type for a deduction guide generated from an inherited constructor
+// [over.match.class.deduct]p1.10:
+// ... the set contains the guides of A with the return type R
+// of each guide replaced with `typename CC<R>::type` ...
+std::pair<TypeSourceInfo *, QualType>
+buildInheritedConstructorDeductionGuideType(
+    Sema &SemaRef, TypeSourceInfo *DerivedClassMapperType,
+    TemplateDecl *DeducingTemplate, TypeSourceInfo *SourceGuideTSI) {
+  auto &Context = SemaRef.Context;
+  const auto *FPT = SourceGuideTSI->getType()->getAs<FunctionProtoType>();
+  assert(FPT && "Source Guide type should be a FunctionProtoType");
+
+  // This substitution can fail in cases where the source return type
+  // is not dependent and the derived class is not deducible
+  Sema::SFINAETrap Trap(SemaRef);
+
+  MultiLevelTemplateArgumentList Args;
+  Args.addOuterTemplateArguments(DeducingTemplate,
+                                 TemplateArgument(FPT->getReturnType()), false);
+  Args.addOuterRetainedLevels(DeducingTemplate->getTemplateDepth());
+  TypeSourceInfo *ReturnTypeTSI =
+      SemaRef.SubstType(DerivedClassMapperType, Args,
+                        DeducingTemplate->getBeginLoc(), DeclarationName());
+  if (!ReturnTypeTSI || Trap.hasErrorOccurred())
+    return {nullptr, QualType()};
+  QualType ReturnType = ReturnTypeTSI->getType();
+
+  TypeLocBuilder TLB;
+  TLB.pushFullCopy(ReturnTypeTSI->getTypeLoc());
+
+  QualType FT = Context.getFunctionType(ReturnType, FPT->getParamTypes(),
+                                        FPT->getExtProtoInfo());
+  FunctionProtoTypeLoc NewTL = TLB.push<FunctionProtoTypeLoc>(FT);
+  const auto &TL = SourceGuideTSI->getTypeLoc().getAs<FunctionProtoTypeLoc>();
+  NewTL.setLocalRangeBegin(TL.getLocalRangeBegin());
+  NewTL.setLParenLoc(TL.getLParenLoc());
+  NewTL.setRParenLoc(TL.getRParenLoc());
+  NewTL.setExceptionSpecRange(TL.getExceptionSpecRange());
+  NewTL.setLocalRangeEnd(TL.getLocalRangeEnd());
+  for (unsigned I = 0, E = NewTL.getNumParams(); I != E; ++I)
+    NewTL.setParam(I, TL.getParam(I));
+
+  TypeSourceInfo *TSI = TLB.getTypeSourceInfo(Context, FT);
+  return {TSI, ReturnType};
+}
+
 // Build deduction guides for a type alias template from the given underlying
 // deduction guide F.
-FunctionTemplateDecl *
-BuildDeductionGuideForTypeAlias(Sema &SemaRef,
-                                TypeAliasTemplateDecl *AliasTemplate,
-                                FunctionTemplateDecl *F, SourceLocation Loc) {
+FunctionTemplateDecl *BuildDeductionGuideForTypeAlias(
+    Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate,
+    FunctionTemplateDecl *F, SourceLocation Loc,
+    TemplateDecl *DeducingTemplate = nullptr,
+    TypeSourceInfo *DerivedClassMapperType = nullptr) {
   LocalInstantiationScope Scope(SemaRef);
   Sema::InstantiatingTemplate BuildingDeductionGuides(
       SemaRef, AliasTemplate->getLocation(), F,
       Sema::InstantiatingTemplate::BuildingDeductionGuidesTag{});
   if (BuildingDeductionGuides.isInvalid())
     return nullptr;
 
+  if (!DeducingTemplate)
+    DeducingTemplate = AliasTemplate;
----------------
antangelo wrote:

Done

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