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[Clang] Handle default template arguments for alias CTAD guides (#134807)
It's possible that some deduced template arguments come from default arguments, not just from the return type. So we need to recursively visit the default arguments of the parameter if it's referenced, thereby the template parameter referenced by the defualt arguments could come along to the synthesized deduction guide. Fixes #134471
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‎clang/docs/ReleaseNotes.rst

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@@ -471,6 +471,7 @@ Bug Fixes to C++ Support
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- Clang no longer crashes when trying to unify the types of arrays with
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certain differences in qualifiers (this could happen during template argument
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deduction or when building a ternary operator). (#GH97005)
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- Fixed type alias CTAD issues involving default template arguments. (#GH134471)
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- The initialization kind of elements of structured bindings
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direct-list-initialized from an array is corrected to direct-initialization.
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- Clang no longer crashes when a coroutine is declared ``[[noreturn]]``. (#GH127327)

‎clang/lib/Sema/SemaTemplateDeductionGuide.cpp

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@@ -690,6 +690,26 @@ SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
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SemaRef.MarkUsedTemplateParameters(
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DeducedArgs, TemplateParamsList->getDepth(), ReferencedTemplateParams);
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auto MarkDefaultArgs = [&](auto *Param) {
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if (!Param->hasDefaultArgument())
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return;
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SemaRef.MarkUsedTemplateParameters(
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Param->getDefaultArgument().getArgument(),
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TemplateParamsList->getDepth(), ReferencedTemplateParams);
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};
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for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
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if (!ReferencedTemplateParams[Index])
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continue;
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auto *Param = TemplateParamsList->getParam(Index);
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if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(Param))
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MarkDefaultArgs(TTPD);
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else if (auto *NTTPD = dyn_cast<NonTypeTemplateParmDecl>(Param))
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MarkDefaultArgs(NTTPD);
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else
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MarkDefaultArgs(cast<TemplateTemplateParmDecl>(Param));
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}
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SmallVector<unsigned> Results;
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for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
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if (ReferencedTemplateParams[Index])

‎clang/test/SemaTemplate/deduction-guide.cpp

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@@ -1,4 +1,4 @@
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// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s --strict-whitespace
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// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s --strict-whitespace -dump-input=always
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template<auto ...> struct X {};
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template<template<typename X, X> typename> struct Y {};
@@ -771,3 +771,118 @@ D d(24);
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// CHECK-NEXT: `-ParmVarDecl {{.+}} 'U'
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} // namespace GH132616_DeductionGuide
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namespace GH133132 {
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template <class _Ty>
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struct A {};
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template <class T = int, class U = T>
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using AA = A<U>;
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AA a{};
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// CHECK-LABEL: Dumping GH133132::<deduction guide for AA>:
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// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for AA>
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// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 0 T
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// CHECK-NEXT: | `-TemplateArgument type 'int'
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// CHECK-NEXT: | `-BuiltinType {{.+}} 'int'
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// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
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// CHECK-NEXT: | `-TemplateArgument type 'T':'type-parameter-0-0'
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// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'T' dependent depth 0 index 0
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// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'T'
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// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
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// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::AA' dependent
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// CHECK-NEXT: | | `-name: 'GH133132::AA'
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// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} AA
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// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
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// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
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// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
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// CHECK-NEXT: | `-TemplateArgument type 'U':'type-parameter-0-1'
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// CHECK-NEXT: | `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
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// CHECK-NEXT: | |-FunctionTemplate {{.+}} '<deduction guide for A>'
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// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
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// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'U'
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// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for AA> 'auto () -> A<U>'
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// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for AA> 'auto () -> A<int>' implicit_instantiation
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// CHECK-NEXT: |-TemplateArgument type 'int'
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// CHECK-NEXT: | `-BuiltinType {{.+}} 'int'
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// CHECK-NEXT: `-TemplateArgument type 'int'
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// CHECK-NEXT: `-BuiltinType {{.+}} 'int'
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template <template <class> class _X>
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struct B {};
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template <template <class> class _X = A, template <class> class _Y = _X>
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using BB = B<_Y>;
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BB b{};
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// CHECK-LABEL: Dumping GH133132::<deduction guide for BB>:
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// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for BB>
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// CHECK-NEXT: |-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
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// CHECK-NEXT: | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
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// CHECK-NEXT: | `-TemplateArgument {{.+}} template 'A':'GH133132::A' qualified
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// CHECK-NEXT: | `-ClassTemplateDecl {{.+}} A
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// CHECK-NEXT: |-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
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// CHECK-NEXT: | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
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// CHECK-NEXT: | `-TemplateArgument {{.+}} template '_X':'template-parameter-0-0' qualified
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// CHECK-NEXT: | `-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
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// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
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// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::BB' dependent
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// CHECK-NEXT: | | `-name: 'GH133132::BB'
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// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} BB
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// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'B<_Y>' dependent
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// CHECK-NEXT: | |-name: 'B':'GH133132::B' qualified
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// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} B
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// CHECK-NEXT: | `-TemplateArgument template '_Y':'template-parameter-0-1' subst index 0
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// CHECK-NEXT: | |-parameter: TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
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// CHECK-NEXT: | |-associated FunctionTemplate {{.+}} '<deduction guide for B>'
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// CHECK-NEXT: | `-replacement: '_Y':'template-parameter-0-1' qualified
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// CHECK-NEXT: | `-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
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// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for BB> 'auto () -> B<_Y>'
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// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for BB> 'auto () -> B<GH133132::A>' implicit_instantiation
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// CHECK-NEXT: |-TemplateArgument template 'GH133132::A'
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// CHECK-NEXT: | `-ClassTemplateDecl {{.+}} A
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// CHECK-NEXT: `-TemplateArgument template 'GH133132::A'
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// CHECK-NEXT: `-ClassTemplateDecl {{.+}} A
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template <int N = 42, class U = A<decltype(N)>>
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using CC = A<U>;
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CC c{};
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// CHECK-LABEL: Dumping GH133132::<deduction guide for CC>:
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// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for CC>
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// CHECK-NEXT: |-NonTypeTemplateParmDecl {{.+}} 'int' depth 0 index 0 N
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// CHECK-NEXT: | `-TemplateArgument {{.+}} expr '42'
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// CHECK-NEXT: | `-IntegerLiteral {{.+}} 'int' 42
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// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
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// CHECK-NEXT: | `-TemplateArgument type 'A<decltype(N)>'
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// CHECK-NEXT: | `-ElaboratedType {{.+}} 'A<decltype(N)>' sugar dependent
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// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<decltype(N)>' dependent
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// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
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// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
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// CHECK-NEXT: | `-TemplateArgument type 'decltype(N)'
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// CHECK-NEXT: | `-DecltypeType {{.+}} 'decltype(N)' dependent
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// CHECK-NEXT: | `-DeclRefExpr {{.+}} 'int' NonTypeTemplateParm {{.+}} 'N' 'int'
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// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
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// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::CC' dependent
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// CHECK-NEXT: | | `-name: 'GH133132::CC'
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// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} CC
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// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
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// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
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// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
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// CHECK-NEXT: | `-TemplateArgument type 'U':'type-parameter-0-1'
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// CHECK-NEXT: | `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
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// CHECK-NEXT: | |-FunctionTemplate {{.+}} '<deduction guide for A>'
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// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
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// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'U'
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// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for CC> 'auto () -> A<U>'
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// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for CC> 'auto () -> A<GH133132::A<int>>' implicit_instantiation
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// CHECK-NEXT: |-TemplateArgument integral '42'
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// CHECK-NEXT: `-TemplateArgument type 'GH133132::A<int>'
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// CHECK-NEXT: `-RecordType {{.+}} 'GH133132::A<int>'
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// CHECK-NEXT: `-ClassTemplateSpecialization {{.+}} 'A'
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}

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