[clang] CTAD alias: fix transformation for require-clause expr Part2. (#93533)

In the #90961 fix, we miss a
case where the undeduced template parameters of the underlying deduction
guide are not transformed, which leaves incorrect depth/index
information, and causes crashes when evaluating constraints.

This patch fix this missing case.

Fixes #92596
Fixes #92212

Author: hokein

clang/lib/Sema/SemaTemplate.cpp

@@ -2743,7 +2743,7 @@ Expr *
 buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
                            TypeAliasTemplateDecl *AliasTemplate,
                            ArrayRef<DeducedTemplateArgument> DeduceResults,
-                           Expr *IsDeducible) {
+                           unsigned FirstUndeducedParamIdx, Expr *IsDeducible) {
   Expr *RC = F->getTemplateParameters()->getRequiresClause();
   if (!RC)
     return IsDeducible;
@@ -2803,8 +2803,22 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
 
   for (unsigned Index = 0; Index < DeduceResults.size(); ++Index) {
     const auto &D = DeduceResults[Index];
-    if (D.isNull())
+    if (D.isNull()) { // non-deduced template parameters of f
+      NamedDecl *TP = F->getTemplateParameters()->getParam(Index);
+      MultiLevelTemplateArgumentList Args;
+      Args.setKind(TemplateSubstitutionKind::Rewrite);
+      Args.addOuterTemplateArguments(TemplateArgsForBuildingRC);
+      // Rebuild the template parameter with updated depth and index.
+      NamedDecl *NewParam = transformTemplateParameter(
+          SemaRef, F->getDeclContext(), TP, Args,
+          /*NewIndex=*/FirstUndeducedParamIdx,
+          getTemplateParameterDepth(TP) + AdjustDepth);
+      FirstUndeducedParamIdx += 1;
+      assert(TemplateArgsForBuildingRC[Index].isNull());
+      TemplateArgsForBuildingRC[Index] = Context.getCanonicalTemplateArgument(
+          Context.getInjectedTemplateArg(NewParam));
       continue;
+    }
     TemplateArgumentLoc Input =
         SemaRef.getTrivialTemplateArgumentLoc(D, QualType(), SourceLocation{});
     TemplateArgumentLoc Output;
@@ -2820,8 +2834,8 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
   MultiLevelTemplateArgumentList ArgsForBuildingRC;
   ArgsForBuildingRC.setKind(clang::TemplateSubstitutionKind::Rewrite);
   ArgsForBuildingRC.addOuterTemplateArguments(TemplateArgsForBuildingRC);
-  // For 2), if the underlying F is instantiated from a member template, we need
-  // the entire template argument list, as the constraint AST in the
+  // For 2), if the underlying deduction guide F is nested in a class template,
+  // we need the entire template argument list, as the constraint AST in the
   // require-clause of F remains completely uninstantiated.
   //
   // For example:
@@ -2845,7 +2859,13 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
   // We add the outer template arguments which is [int] to the multi-level arg
   // list to ensure that the occurrence U in `C<U>` will be replaced with int
   // during the substitution.
-  if (F->getInstantiatedFromMemberTemplate()) {
+  //
+  // NOTE: The underlying deduction guide F is instantiated -- either from an
+  // explicitly-written deduction guide member, or from a constructor.
+  // getInstantiatedFromMemberTemplate() can only handle the former case, so we
+  // check the DeclContext kind.
+  if (F->getLexicalDeclContext()->getDeclKind() ==
+      clang::Decl::ClassTemplateSpecialization) {
     auto OuterLevelArgs = SemaRef.getTemplateInstantiationArgs(
         F, F->getLexicalDeclContext(),
         /*Final=*/false, /*Innermost=*/std::nullopt,
@@ -3063,6 +3083,7 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
         Context.getInjectedTemplateArg(NewParam));
     TransformedDeducedAliasArgs[AliasTemplateParamIdx] = NewTemplateArgument;
   }
+  unsigned FirstUndeducedParamIdx = FPrimeTemplateParams.size();
   //   ...followed by the template parameters of f that were not deduced
   //   (including their default template arguments)
   for (unsigned FTemplateParamIdx : NonDeducedTemplateParamsInFIndex) {
@@ -3131,8 +3152,9 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
 
     Expr *IsDeducible = buildIsDeducibleConstraint(
         SemaRef, AliasTemplate, FPrime->getReturnType(), FPrimeTemplateParams);
-    Expr *RequiresClause = buildAssociatedConstraints(
-        SemaRef, F, AliasTemplate, DeduceResults, IsDeducible);
+    Expr *RequiresClause =
+        buildAssociatedConstraints(SemaRef, F, AliasTemplate, DeduceResults,
+                                   FirstUndeducedParamIdx, IsDeducible);
 
     auto *FPrimeTemplateParamList = TemplateParameterList::Create(
         Context, AliasTemplate->getTemplateParameters()->getTemplateLoc(),

clang/test/AST/ast-dump-ctad-alias.cpp

@@ -53,6 +53,33 @@ Out2<double>::AInner t(1.0);
 // CHECK-NEXT: |       | `-BuiltinType {{.*}} 'double'
 // CHECK-NEXT: |       `-ParmVarDecl {{.*}} 'double'
 
+// GH92596
+template <typename T0>
+struct Out3 {
+  template<class T1, typename T2>
+  struct Foo {
+    // Deduction guide:
+    //   template <typename T1, typename T2, typename V>
+    //   Foo(V, T1) -> Foo<T1, T2>;
+    template<class V> requires Concept<T0, V> // V in require clause of Foo deduction guide: depth 1, index: 2
+    Foo(V, T1);
+  };
+};
+template<class T3>
+using AFoo3 = Out3<int>::Foo<T3, T3>;
+AFoo3 afoo3{0, 1};
+// Verify occurrence V in the require-clause is transformed (depth: 1 => 0, index: 2 => 1) correctly.
+
+// CHECK:      FunctionTemplateDecl {{.*}} implicit <deduction guide for AFoo3>
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.*}} class depth 0 index 0 T3
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.*}} class depth 0 index 1 V
+// CHECK-NEXT: |-BinaryOperator {{.*}} '<dependent type>' '&&'
+// CHECK-NEXT: | |-UnresolvedLookupExpr {{.*}} '<dependent type>' lvalue (no ADL) = 'Concept'
+// CHECK-NEXT: | | |-TemplateArgument type 'int'
+// CHECK-NEXT: | | | `-BuiltinType {{.*}} 'int'
+// CHECK-NEXT: | | `-TemplateArgument type 'type-parameter-0-1'
+// CHECK-NEXT: | |   `-TemplateTypeParmType {{.*}} 'type-parameter-0-1' dependent depth 0 index 1
+
 template <typename... T1>
 struct Foo {
   Foo(T1...);

clang/test/SemaCXX/cxx20-ctad-type-alias.cpp

@@ -266,7 +266,7 @@ template <typename U>
 using Bar = Foo<U>; // expected-note {{could not match 'Foo<type-parameter-0-0>' against 'int'}} \
                     // expected-note {{implicit deduction guide declared as 'template <typename U> requires __is_deducible(test18::Bar, Foo<type-parameter-0-0>) Bar(Foo<type-parameter-0-0>) -> Foo<type-parameter-0-0>'}} \
                     // expected-note {{candidate template ignored: constraints not satisfied}} \
-                    // expected-note {{implicit deduction guide declared as 'template <typename T> requires False<T> && __is_deducible(test18::Bar, Foo<int>) Bar(type-parameter-0-0) -> Foo<int>'}} \
+                    // expected-note {{implicit deduction guide declared as 'template <typename T> requires False<type-parameter-0-0> && __is_deducible(test18::Bar, Foo<int>) Bar(type-parameter-0-0) -> Foo<int>'}} \
                     // expected-note {{candidate function template not viable}} \
                     // expected-note {{implicit deduction guide declared as 'template <typename U> requires __is_deducible(test18::Bar, Foo<type-parameter-0-0>) Bar() -> Foo<type-parameter-0-0>'}}
 
@@ -414,4 +414,29 @@ struct A1 {
 template <typename U>
 using AFoo = A1<int>::A2<int>::Foo<U>;
 AFoo case3(1);
+
+// Case4: crashes on the constexpr evaluator due to the mixed-up index for the
+// template parameters `V`.
+template<class T, typename T2>
+struct Case4 {
+  template<class V> requires C<V>
+  Case4(V, T);
+};
+
+template<class T2>
+using ACase4 = Case4<T2, T2>;
+ACase4 case4{0, 1};
+
 } // namespace test24
+
+namespace GH92212 {
+template<typename T, typename...Us>
+struct A{
+  template<typename V> requires __is_same(V, int)
+  A(V);
+};
+
+template<typename...TS>
+using AA = A<int, TS...>;
+AA a{0};
+}