[clang] de528d6 - [Clang] Handle default template arguments for alias CTAD guides (#134807)
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Wed Apr 16 19:08:53 PDT 2025
Author: Younan Zhang
Date: 2025-04-17T10:08:50+08:00
New Revision: de528d689f3a2305c051528993fe30295f2a0cd9
URL: https://github.com/llvm/llvm-project/commit/de528d689f3a2305c051528993fe30295f2a0cd9
DIFF: https://github.com/llvm/llvm-project/commit/de528d689f3a2305c051528993fe30295f2a0cd9.diff
LOG: [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 https://github.com/llvm/llvm-project/issues/134471
Added:
Modified:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaTemplateDeductionGuide.cpp
clang/test/SemaTemplate/deduction-guide.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 07ff1251fc1ad..0bf5e07ec5dfd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -471,6 +471,7 @@ Bug Fixes to C++ Support
- Clang no longer crashes when trying to unify the types of arrays with
certain
diff erences in qualifiers (this could happen during template argument
deduction or when building a ternary operator). (#GH97005)
+- Fixed type alias CTAD issues involving default template arguments. (#GH134471)
- The initialization kind of elements of structured bindings
direct-list-initialized from an array is corrected to direct-initialization.
- Clang no longer crashes when a coroutine is declared ``[[noreturn]]``. (#GH127327)
diff --git a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
index b4863cefc3fb4..29c5736a9bf9e 100644
--- a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
+++ b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
@@ -690,6 +690,26 @@ SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
SemaRef.MarkUsedTemplateParameters(
DeducedArgs, TemplateParamsList->getDepth(), ReferencedTemplateParams);
+ auto MarkDefaultArgs = [&](auto *Param) {
+ if (!Param->hasDefaultArgument())
+ return;
+ SemaRef.MarkUsedTemplateParameters(
+ Param->getDefaultArgument().getArgument(),
+ TemplateParamsList->getDepth(), ReferencedTemplateParams);
+ };
+
+ for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
+ if (!ReferencedTemplateParams[Index])
+ continue;
+ auto *Param = TemplateParamsList->getParam(Index);
+ if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(Param))
+ MarkDefaultArgs(TTPD);
+ else if (auto *NTTPD = dyn_cast<NonTypeTemplateParmDecl>(Param))
+ MarkDefaultArgs(NTTPD);
+ else
+ MarkDefaultArgs(cast<TemplateTemplateParmDecl>(Param));
+ }
+
SmallVector<unsigned> Results;
for (unsigned Index = 0; Index < TemplateParamsList->size(); ++Index) {
if (ReferencedTemplateParams[Index])
diff --git a/clang/test/SemaTemplate/deduction-guide.cpp b/clang/test/SemaTemplate/deduction-guide.cpp
index 2888453a12f5b..dabd0cf12f77e 100644
--- a/clang/test/SemaTemplate/deduction-guide.cpp
+++ b/clang/test/SemaTemplate/deduction-guide.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s --strict-whitespace
+// 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
template<auto ...> struct X {};
template<template<typename X, X> typename> struct Y {};
@@ -771,3 +771,118 @@ D d(24);
// CHECK-NEXT: `-ParmVarDecl {{.+}} 'U'
} // namespace GH132616_DeductionGuide
+
+namespace GH133132 {
+
+template <class _Ty>
+struct A {};
+
+template <class T = int, class U = T>
+using AA = A<U>;
+
+AA a{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for AA>:
+// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for AA>
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 0 T
+// CHECK-NEXT: | `-TemplateArgument type 'int'
+// CHECK-NEXT: | `-BuiltinType {{.+}} 'int'
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
+// CHECK-NEXT: | `-TemplateArgument type 'T':'type-parameter-0-0'
+// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'T' dependent depth 0 index 0
+// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'T'
+// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::AA' dependent
+// CHECK-NEXT: | | `-name: 'GH133132::AA'
+// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} AA
+// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
+// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT: | `-TemplateArgument type 'U':'type-parameter-0-1'
+// CHECK-NEXT: | `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
+// CHECK-NEXT: | |-FunctionTemplate {{.+}} '<deduction guide for A>'
+// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
+// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'U'
+// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for AA> 'auto () -> A<U>'
+// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for AA> 'auto () -> A<int>' implicit_instantiation
+// CHECK-NEXT: |-TemplateArgument type 'int'
+// CHECK-NEXT: | `-BuiltinType {{.+}} 'int'
+// CHECK-NEXT: `-TemplateArgument type 'int'
+// CHECK-NEXT: `-BuiltinType {{.+}} 'int'
+
+template <template <class> class _X>
+struct B {};
+
+template <template <class> class _X = A, template <class> class _Y = _X>
+using BB = B<_Y>;
+
+BB b{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for BB>:
+// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for BB>
+// CHECK-NEXT: |-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT: | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
+// CHECK-NEXT: | `-TemplateArgument {{.+}} template 'A':'GH133132::A' qualified
+// CHECK-NEXT: | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT: |-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
+// CHECK-NEXT: | |-TemplateTypeParmDecl {{.+}} class depth 0 index 0
+// CHECK-NEXT: | `-TemplateArgument {{.+}} template '_X':'template-parameter-0-0' qualified
+// CHECK-NEXT: | `-TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::BB' dependent
+// CHECK-NEXT: | | `-name: 'GH133132::BB'
+// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} BB
+// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'B<_Y>' dependent
+// CHECK-NEXT: | |-name: 'B':'GH133132::B' qualified
+// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} B
+// CHECK-NEXT: | `-TemplateArgument template '_Y':'template-parameter-0-1' subst index 0
+// CHECK-NEXT: | |-parameter: TemplateTemplateParmDecl {{.+}} depth 0 index 0 _X
+// CHECK-NEXT: | |-associated FunctionTemplate {{.+}} '<deduction guide for B>'
+// CHECK-NEXT: | `-replacement: '_Y':'template-parameter-0-1' qualified
+// CHECK-NEXT: | `-TemplateTemplateParmDecl {{.+}} depth 0 index 1 _Y
+// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for BB> 'auto () -> B<_Y>'
+// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for BB> 'auto () -> B<GH133132::A>' implicit_instantiation
+// CHECK-NEXT: |-TemplateArgument template 'GH133132::A'
+// CHECK-NEXT: | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT: `-TemplateArgument template 'GH133132::A'
+// CHECK-NEXT: `-ClassTemplateDecl {{.+}} A
+
+template <int N = 42, class U = A<decltype(N)>>
+using CC = A<U>;
+
+CC c{};
+
+// CHECK-LABEL: Dumping GH133132::<deduction guide for CC>:
+// CHECK-NEXT: FunctionTemplateDecl {{.+}} implicit <deduction guide for CC>
+// CHECK-NEXT: |-NonTypeTemplateParmDecl {{.+}} 'int' depth 0 index 0 N
+// CHECK-NEXT: | `-TemplateArgument {{.+}} expr '42'
+// CHECK-NEXT: | `-IntegerLiteral {{.+}} 'int' 42
+// CHECK-NEXT: |-TemplateTypeParmDecl {{.+}} class depth 0 index 1 U
+// CHECK-NEXT: | `-TemplateArgument type 'A<decltype(N)>'
+// CHECK-NEXT: | `-ElaboratedType {{.+}} 'A<decltype(N)>' sugar dependent
+// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<decltype(N)>' dependent
+// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT: | `-TemplateArgument type 'decltype(N)'
+// CHECK-NEXT: | `-DecltypeType {{.+}} 'decltype(N)' dependent
+// CHECK-NEXT: | `-DeclRefExpr {{.+}} 'int' NonTypeTemplateParm {{.+}} 'N' 'int'
+// CHECK-NEXT: |-TypeTraitExpr {{.+}} 'bool' __is_deducible
+// CHECK-NEXT: | |-DeducedTemplateSpecializationType {{.+}} 'GH133132::CC' dependent
+// CHECK-NEXT: | | `-name: 'GH133132::CC'
+// CHECK-NEXT: | | `-TypeAliasTemplateDecl {{.+}} CC
+// CHECK-NEXT: | `-TemplateSpecializationType {{.+}} 'A<U>' dependent
+// CHECK-NEXT: | |-name: 'A':'GH133132::A' qualified
+// CHECK-NEXT: | | `-ClassTemplateDecl {{.+}} A
+// CHECK-NEXT: | `-TemplateArgument type 'U':'type-parameter-0-1'
+// CHECK-NEXT: | `-SubstTemplateTypeParmType {{.+}} 'U' sugar dependent class depth 0 index 0 _Ty
+// CHECK-NEXT: | |-FunctionTemplate {{.+}} '<deduction guide for A>'
+// CHECK-NEXT: | `-TemplateTypeParmType {{.+}} 'U' dependent depth 0 index 1
+// CHECK-NEXT: | `-TemplateTypeParm {{.+}} 'U'
+// CHECK-NEXT: |-CXXDeductionGuideDecl {{.+}} implicit <deduction guide for CC> 'auto () -> A<U>'
+// CHECK-NEXT: `-CXXDeductionGuideDecl {{.+}} implicit used <deduction guide for CC> 'auto () -> A<GH133132::A<int>>' implicit_instantiation
+// CHECK-NEXT: |-TemplateArgument integral '42'
+// CHECK-NEXT: `-TemplateArgument type 'GH133132::A<int>'
+// CHECK-NEXT: `-RecordType {{.+}} 'GH133132::A<int>'
+// CHECK-NEXT: `-ClassTemplateSpecialization {{.+}} 'A'
+
+}
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