[clang] [clang] CTAD: Fix require-clause is not transformed. (PR #89378)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Haojian Wu (hokein)

<details>
<summary>Changes</summary>

Fixes https://github.com/llvm/llvm-project/issues/89013

When building the deduction guide, we use the TemplateArgsForBuildingFPrime to transform the require-clause from the underlying class deduction guide. However, we do this at the wrong place where not all elements of TemplateArgsForBuildingFPrime are initialized. The fix involves rearranging the transformRequireClause call to the correct location.

As part of the fix, we extend the TemplateInstantiator to support more types in the template-rewrite mode. Otherwise, we will encounter an assertion error when attempting to rewrite the template type parameter type like D with a complex type like Derived<U>.

---
Full diff: https://github.com/llvm/llvm-project/pull/89378.diff


4 Files Affected:

- (modified) clang/lib/Sema/SemaTemplate.cpp (+14-13) 
- (modified) clang/lib/Sema/SemaTemplateInstantiate.cpp (+1-4) 
- (modified) clang/test/SemaCXX/cxx20-ctad-type-alias.cpp (+18) 
- (modified) clang/test/SemaTemplate/deduction-guide.cpp (+28) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d4976f9d0d11d8..4bda31ba67c02d 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2962,19 +2962,6 @@ void DeclareImplicitDeductionGuidesForTypeAlias(
           Context.getCanonicalTemplateArgument(
               Context.getInjectedTemplateArg(NewParam));
     }
-    // Substitute new template parameters into requires-clause if present.
-    Expr *RequiresClause =
-        transformRequireClause(SemaRef, F, TemplateArgsForBuildingFPrime);
-    // FIXME: implement the is_deducible constraint per C++
-    // [over.match.class.deduct]p3.3:
-    //    ... and a constraint that is satisfied if and only if the arguments
-    //    of A are deducible (see below) from the return type.
-    auto *FPrimeTemplateParamList = TemplateParameterList::Create(
-        Context, AliasTemplate->getTemplateParameters()->getTemplateLoc(),
-        AliasTemplate->getTemplateParameters()->getLAngleLoc(),
-        FPrimeTemplateParams,
-        AliasTemplate->getTemplateParameters()->getRAngleLoc(),
-        /*RequiresClause=*/RequiresClause);
 
     // To form a deduction guide f' from f, we leverage clang's instantiation
     // mechanism, we construct a template argument list where the template
@@ -3020,6 +3007,20 @@ void DeclareImplicitDeductionGuidesForTypeAlias(
             F, TemplateArgListForBuildingFPrime, AliasTemplate->getLocation(),
             Sema::CodeSynthesisContext::BuildingDeductionGuides)) {
       auto *GG = cast<CXXDeductionGuideDecl>(FPrime);
+      // Substitute new template parameters into requires-clause if present.
+      Expr *RequiresClause =
+          transformRequireClause(SemaRef, F, TemplateArgsForBuildingFPrime);
+      // FIXME: implement the is_deducible constraint per C++
+      // [over.match.class.deduct]p3.3:
+      //    ... and a constraint that is satisfied if and only if the arguments
+      //    of A are deducible (see below) from the return type.
+      auto *FPrimeTemplateParamList = TemplateParameterList::Create(
+          Context, AliasTemplate->getTemplateParameters()->getTemplateLoc(),
+          AliasTemplate->getTemplateParameters()->getLAngleLoc(),
+          FPrimeTemplateParams,
+          AliasTemplate->getTemplateParameters()->getRAngleLoc(),
+          /*RequiresClause=*/RequiresClause);
+
       buildDeductionGuide(SemaRef, AliasTemplate, FPrimeTemplateParamList,
                           GG->getCorrespondingConstructor(),
                           GG->getExplicitSpecifier(), GG->getTypeSourceInfo(),
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 7cd428de0bb32d..63894cc3cdd538 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -2501,10 +2501,7 @@ TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
       assert(Arg.getKind() == TemplateArgument::Type &&
              "unexpected nontype template argument kind in template rewrite");
       QualType NewT = Arg.getAsType();
-      assert(isa<TemplateTypeParmType>(NewT) &&
-             "type parm not rewritten to type parm");
-      auto NewTL = TLB.push<TemplateTypeParmTypeLoc>(NewT);
-      NewTL.setNameLoc(TL.getNameLoc());
+      TLB.pushTrivial(SemaRef.Context, NewT, TL.getNameLoc());
       return NewT;
     }
 
diff --git a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
index 6f04264a655ad5..508a3a5da76a91 100644
--- a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
+++ b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
@@ -289,3 +289,21 @@ using String = Array<char, N>;
 // Verify no crash on constructing the aggregate deduction guides.
 String s("hello");
 } // namespace test21
+
+// GH89013
+namespace test22 {
+class Base {};
+template <typename T>
+class Derived final : public Base {};
+
+template <typename T, typename D>
+requires __is_base_of(Base, D)
+struct Foo {
+  explicit Foo(D) {}
+};
+
+template <typename U>
+using AFoo = Foo<int, Derived<U>>;
+
+AFoo a(Derived<int>{});
+} // namespace test22
diff --git a/clang/test/SemaTemplate/deduction-guide.cpp b/clang/test/SemaTemplate/deduction-guide.cpp
index 58f08aa1eed650..29cc5a9b996f95 100644
--- a/clang/test/SemaTemplate/deduction-guide.cpp
+++ b/clang/test/SemaTemplate/deduction-guide.cpp
@@ -260,3 +260,31 @@ AG ag = {1};
 // CHECK:   |-TemplateArgument type 'int'
 // CHECK:   | `-BuiltinType {{.*}} 'int'
 // CHECK:   `-ParmVarDecl {{.*}} 'int'
+
+template <typename D>
+requires (sizeof(D) == 4)
+struct Foo {
+  Foo(D);
+};
+
+template <typename U>
+using AFoo = Foo<G<U>>;
+// Verify that the require-clause from the Foo deduction guide is transformed.
+// The D occurrence should be rewritten to G<type-parameter-0-0>.
+//
+// CHECK-LABEL: Dumping <deduction guide for AFoo>
+// CHECK: FunctionTemplateDecl {{.*}} implicit <deduction guide for AFoo>
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.*}} typename depth 0 index 0 U
+// CHECK-NEXT: |-ParenExpr {{.*}} 'bool'
+// CHECK-NEXT: | `-BinaryOperator {{.*}} 'bool' '=='
+// CHECK-NEXT: |   |-UnaryExprOrTypeTraitExpr {{.*}} 'unsigned long' sizeof 'G<type-parameter-0-0>'
+// CHECK-NEXT: |   `-ImplicitCastExpr {{.*}} 'unsigned long' <IntegralCast>
+// CHECK-NEXT: |     `-IntegerLiteral {{.*}} 'int' 4
+// CHECK-NEXT: |-CXXDeductionGuideDecl {{.*}} implicit <deduction guide for AFoo> 'auto (G<type-parameter-0-0>) -> Foo<G<type-parameter-0-0>>'
+// CHECK-NEXT: | `-ParmVarDecl {{.*}} 'G<type-parameter-0-0>'
+// CHECK-NEXT: `-CXXDeductionGuideDecl {{.*}} implicit used <deduction guide for AFoo> 'auto (G<int>) -> Foo<G<int>>' implicit_instantiation
+// CHECK-NEXT:   |-TemplateArgument type 'int'
+// CHECK-NEXT:   | `-BuiltinType {{.*}} 'int'
+// CHECK-NEXT:   `-ParmVarDecl {{.*}} 'G<int>'
+
+AFoo aa(G<int>{});

``````````

</details>


https://github.com/llvm/llvm-project/pull/89378