release/21.x: [Clang] Fix a partial ordering bug involving CTAD injected template arguments (#149782)

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -5525,6 +5525,15 @@ static TemplateDeductionResult CheckDeductionConsistency(
   // FIXME: A substitution can be incomplete on a non-structural part of the
   // type. Use the canonical type for now, until the TemplateInstantiator can
   // deal with that.
+
+  // Workaround: Implicit deduction guides use InjectedClassNameTypes, whereas
+  // the explicit guides don't. The substitution doesn't transform these types,
+  // so let it transform their specializations instead.
+  bool IsDeductionGuide = isa<CXXDeductionGuideDecl>(FTD->getTemplatedDecl());
+  if (IsDeductionGuide) {
+    if (auto *Injected = P->getAs<InjectedClassNameType>())
+      P = Injected->getInjectedSpecializationType();
+  }
   QualType InstP = S.SubstType(P.getCanonicalType(), MLTAL, FTD->getLocation(),
                                FTD->getDeclName(), &IsIncompleteSubstitution);
   if (InstP.isNull() && !IsIncompleteSubstitution)
@@ -5539,9 +5548,15 @@ static TemplateDeductionResult CheckDeductionConsistency(
   if (auto *PA = dyn_cast<PackExpansionType>(A);
       PA && !isa<PackExpansionType>(InstP))
     A = PA->getPattern();
-  if (!S.Context.hasSameType(
-          S.Context.getUnqualifiedArrayType(InstP.getNonReferenceType()),
-          S.Context.getUnqualifiedArrayType(A.getNonReferenceType())))
+  auto T1 = S.Context.getUnqualifiedArrayType(InstP.getNonReferenceType());
+  auto T2 = S.Context.getUnqualifiedArrayType(A.getNonReferenceType());
+  if (IsDeductionGuide) {
+    if (auto *Injected = T1->getAs<InjectedClassNameType>())
+      T1 = Injected->getInjectedSpecializationType();
+    if (auto *Injected = T2->getAs<InjectedClassNameType>())
+      T2 = Injected->getInjectedSpecializationType();
+  }
+  if (!S.Context.hasSameType(T1, T2))
     return TemplateDeductionResult::NonDeducedMismatch;
   return TemplateDeductionResult::Success;
 }

clang/test/SemaTemplate/deduction-guide.cpp

@@ -966,3 +966,19 @@ Expand<Type, Invocable<>> _{};
 // CHECK-NEXT:   | `-ParmVarDecl {{.+}} 'T...' pack
 
 }
+
+namespace GH134613 {
+template <typename R> struct Foo {
+  using value_type = R;
+
+  Foo() = default;
+  Foo(Foo<Foo<R>> &&rhs) {}
+};
+
+void main() {
+  auto r1 = Foo(Foo<Foo<int>>{});
+
+  static_assert(__is_same(decltype(r1)::value_type, int));
+}
+
+}