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[clang] Remove written template args from implicit var tpl spec #156329

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Merged
merged 1 commit into from
Sep 4, 2025
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[clang] Remove written template args from implicit var tpl spec #156329

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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -84,6 +84,9 @@ C++ Specific Potentially Breaking Changes
static_assert((b.*mp)() == 1); // newly rejected
static_assert((c.*mp)() == 1); // accepted

- ``VarTemplateSpecializationDecl::getTemplateArgsAsWritten()`` method now
returns ``nullptr`` for implicitly instantiated declarations.

ABI Changes in This Version
---------------------------

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4 changes: 2 additions & 2 deletions clang/include/clang/Sema/Sema.h
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Expand Up @@ -11662,7 +11662,8 @@ class Sema final : public SemaBase {
DeclResult CheckVarTemplateId(VarTemplateDecl *Template,
SourceLocation TemplateLoc,
SourceLocation TemplateNameLoc,
const TemplateArgumentListInfo &TemplateArgs);
const TemplateArgumentListInfo &TemplateArgs,
bool SetWrittenArgs);
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Rather than adding a new bool parameter, I think we better move the responsibility of setting the written args entirely out of CheckVarTemplateId, which would make this more similar to CheckTypeTemplateId.

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Setting the args to the CheckVarTemplateId result may change some previous declaration stored in the ASTContext when CheckVarTemplateId returns it and not a new one.

I cannot find CheckTypeTemplateId in the project (typo?)

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Err I meant CheckTemplateIdType, pretty unfortunate inconsistency in naming formulation.

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@mizvekov mizvekov Sep 2, 2025 •
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Right, that's another inconsistency with how CheckTemplateIdType operates and is used.

This may need some though, I don't want to propose a large refactoring to support such a simple change, but the bool parameter does not feel right.

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Seems like the difference is because CheckTemplateIdType returns template specialization type and not the specialization declaration.


/// Form a reference to the specialization of the given variable template
/// corresponding to the specified argument list, or a null-but-valid result
Expand Down Expand Up @@ -14022,7 +14023,6 @@ class Sema final : public SemaBase {
VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
VarTemplateDecl *VarTemplate, VarDecl *FromVar,
const TemplateArgumentList *PartialSpecArgs,
const TemplateArgumentListInfo &TemplateArgsInfo,
SmallVectorImpl<TemplateArgument> &Converted,
SourceLocation PointOfInstantiation,
LateInstantiatedAttrVec *LateAttrs = nullptr,
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3 changes: 1 addition & 2 deletions clang/include/clang/Sema/Template.h
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Expand Up @@ -723,9 +723,8 @@ enum class TemplateSubstitutionKind : char {
bool SubstQualifier(const TagDecl *OldDecl,
TagDecl *NewDecl);

Decl *VisitVarTemplateSpecializationDecl(
VarTemplateSpecializationDecl *VisitVarTemplateSpecializationDecl(
VarTemplateDecl *VarTemplate, VarDecl *FromVar,
const TemplateArgumentListInfo &TemplateArgsInfo,
ArrayRef<TemplateArgument> Converted,
VarTemplateSpecializationDecl *PrevDecl = nullptr);

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5 changes: 3 additions & 2 deletions clang/lib/Sema/SemaExprMember.cpp
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Expand Up @@ -1126,8 +1126,9 @@ Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
return ExprError();
}

DeclResult VDecl = CheckVarTemplateId(VarTempl, TemplateKWLoc,
MemberNameInfo.getLoc(), *TemplateArgs);
DeclResult VDecl =
CheckVarTemplateId(VarTempl, TemplateKWLoc, MemberNameInfo.getLoc(),
*TemplateArgs, /*SetWrittenArgs=*/false);
if (VDecl.isInvalid())
return ExprError();

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16 changes: 10 additions & 6 deletions clang/lib/Sema/SemaTemplate.cpp
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Expand Up @@ -4542,7 +4542,8 @@ static bool IsLibstdcxxStdFormatKind(Preprocessor &PP, VarDecl *Var) {
DeclResult
Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
SourceLocation TemplateNameLoc,
const TemplateArgumentListInfo &TemplateArgs) {
const TemplateArgumentListInfo &TemplateArgs,
bool SetWrittenArgs) {
assert(Template && "A variable template id without template?");

// Check that the template argument list is well-formed for this template.
Expand Down Expand Up @@ -4725,10 +4726,12 @@ Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
// in DoMarkVarDeclReferenced().
// FIXME: LateAttrs et al.?
VarTemplateSpecializationDecl *Decl = BuildVarTemplateInstantiation(
Template, InstantiationPattern, PartialSpecArgs, TemplateArgs,
CTAI.CanonicalConverted, TemplateNameLoc /*, LateAttrs, StartingScope*/);
Template, InstantiationPattern, PartialSpecArgs, CTAI.CanonicalConverted,
TemplateNameLoc /*, LateAttrs, StartingScope*/);
if (!Decl)
return true;
if (SetWrittenArgs)
Decl->setTemplateArgsAsWritten(TemplateArgs);

if (AmbiguousPartialSpec) {
// Partial ordering did not produce a clear winner. Complain.
Expand Down Expand Up @@ -4760,7 +4763,7 @@ ExprResult Sema::CheckVarTemplateId(
const TemplateArgumentListInfo *TemplateArgs) {

DeclResult Decl = CheckVarTemplateId(Template, TemplateLoc, NameInfo.getLoc(),
*TemplateArgs);
*TemplateArgs, /*SetWrittenArgs=*/false);
if (Decl.isInvalid())
return ExprError();

Expand Down Expand Up @@ -10707,8 +10710,9 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
TemplateArgumentListInfo TemplateArgs =
makeTemplateArgumentListInfo(*this, *D.getName().TemplateId);

DeclResult Res = CheckVarTemplateId(PrevTemplate, TemplateLoc,
D.getIdentifierLoc(), TemplateArgs);
DeclResult Res =
CheckVarTemplateId(PrevTemplate, TemplateLoc, D.getIdentifierLoc(),
TemplateArgs, /*SetWrittenArgs=*/true);
if (Res.isInvalid())
return true;

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31 changes: 18 additions & 13 deletions clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
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Expand Up @@ -4542,14 +4542,17 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
PrevDecl->getPointOfInstantiation(), Ignored))
return nullptr;

return VisitVarTemplateSpecializationDecl(InstVarTemplate, D,
VarTemplateArgsInfo,
CTAI.CanonicalConverted, PrevDecl);
if (VarTemplateSpecializationDecl *VTSD = VisitVarTemplateSpecializationDecl(
InstVarTemplate, D, CTAI.CanonicalConverted, PrevDecl)) {
VTSD->setTemplateArgsAsWritten(VarTemplateArgsInfo);
return VTSD;
}
return nullptr;
}

Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
VarTemplateSpecializationDecl *
TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
VarTemplateDecl *VarTemplate, VarDecl *D,
const TemplateArgumentListInfo &TemplateArgsInfo,
ArrayRef<TemplateArgument> Converted,
VarTemplateSpecializationDecl *PrevDecl) {

Expand All @@ -4570,7 +4573,6 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
VarTemplateSpecializationDecl *Var = VarTemplateSpecializationDecl::Create(
SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
VarTemplate, DI->getType(), DI, D->getStorageClass(), Converted);
Var->setTemplateArgsAsWritten(TemplateArgsInfo);
if (!PrevDecl) {
void *InsertPos = nullptr;
VarTemplate->findSpecialization(Converted, InsertPos);
Expand Down Expand Up @@ -5880,7 +5882,6 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
VarTemplateSpecializationDecl *Sema::BuildVarTemplateInstantiation(
VarTemplateDecl *VarTemplate, VarDecl *FromVar,
const TemplateArgumentList *PartialSpecArgs,
const TemplateArgumentListInfo &TemplateArgsInfo,
SmallVectorImpl<TemplateArgument> &Converted,
SourceLocation PointOfInstantiation, LateInstantiatedAttrVec *LateAttrs,
LocalInstantiationScope *StartingScope) {
Expand Down Expand Up @@ -5922,9 +5923,8 @@ VarTemplateSpecializationDecl *Sema::BuildVarTemplateInstantiation(

// TODO: Set LateAttrs and StartingScope ...

return cast_or_null<VarTemplateSpecializationDecl>(
Instantiator.VisitVarTemplateSpecializationDecl(
VarTemplate, FromVar, TemplateArgsInfo, Converted));
return Instantiator.VisitVarTemplateSpecializationDecl(VarTemplate, FromVar,
Converted);
}

VarTemplateSpecializationDecl *Sema::CompleteVarTemplateSpecializationDecl(
Expand Down Expand Up @@ -6340,10 +6340,15 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
TemplateArgInfo.addArgument(Arg);
}

Var = cast_or_null<VarDecl>(Instantiator.VisitVarTemplateSpecializationDecl(
VarSpec->getSpecializedTemplate(), Def, TemplateArgInfo,
VarSpec->getTemplateArgs().asArray(), VarSpec));
VarTemplateSpecializationDecl *VTSD =
Instantiator.VisitVarTemplateSpecializationDecl(
VarSpec->getSpecializedTemplate(), Def,
VarSpec->getTemplateArgs().asArray(), VarSpec);
Var = VTSD;

if (Var) {
VTSD->setTemplateArgsAsWritten(TemplateArgInfo);

llvm::PointerUnion<VarTemplateDecl *,
VarTemplatePartialSpecializationDecl *> PatternPtr =
VarSpec->getSpecializedTemplateOrPartial();
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19 changes: 19 additions & 0 deletions clang/unittests/AST/DeclTest.cpp
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Expand Up @@ -586,3 +586,22 @@ namespace x::y {
ASSERT_NE(FD, nullptr);
ASSERT_EQ(FD->getQualifiedNameAsString(), "x::y::Foo::Foo<T>");
}

TEST(Decl, NoWrittenArgsInImplicitlyInstantiatedVarSpec) {
const char *Code = R"cpp(
template <typename>
int VarTpl;

void fn() {
(void)VarTpl<char>;
}
)cpp";

auto AST = tooling::buildASTFromCode(Code);
ASTContext &Ctx = AST->getASTContext();

const auto *VTSD = selectFirst<VarTemplateSpecializationDecl>(
"id", match(varDecl(isTemplateInstantiation()).bind("id"), Ctx));
ASSERT_NE(VTSD, nullptr);
EXPECT_EQ(VTSD->getTemplateArgsAsWritten(), nullptr);
}