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[Clang] Fix parsing of pack-index-specifier with template-id pattern #3

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[Clang] Fix parsing of pack-index-specifier with template-id pattern #3

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5b04344
[Clang] Fix parsing of pack-index-specifier with template-id pattern
sdkrystian Jan 28, 2026
c5443af
[FOLD] add tests
sdkrystian Jan 28, 2026
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47 changes: 37 additions & 10 deletions clang/lib/Parse/ParseDeclCXX.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1147,8 +1147,9 @@ void Parser::AnnotateExistingDecltypeSpecifier(const DeclSpec &DS,
}

SourceLocation Parser::ParsePackIndexingType(DeclSpec &DS) {
assert(Tok.isOneOf(tok::annot_pack_indexing_type, tok::identifier) &&
"Expected an identifier");
assert(Tok.isOneOf(tok::annot_pack_indexing_type, tok::identifier,
tok::annot_template_id) &&
"Expected an identifier or template-id");

TypeResult Type;
SourceLocation StartLoc;
Expand Down Expand Up @@ -1180,15 +1181,41 @@ SourceLocation Parser::ParsePackIndexingType(DeclSpec &DS) {
return Tok.getEndLoc();
}

ParsedType Ty = Actions.getTypeName(*Tok.getIdentifierInfo(),
Tok.getLocation(), getCurScope());
if (!Ty) {
DS.SetTypeSpecError();
return Tok.getEndLoc();
}
Type = Ty;
if (Tok.is(tok::annot_template_id)) {
TemplateIdAnnotation *TemplateId = takeTemplateIdAnnotation(Tok);
StartLoc = TemplateId->TemplateNameLoc;

StartLoc = ConsumeToken();
ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
TemplateId->NumArgs);
CXXScopeSpec SS;
TypeResult Ty =
TemplateId->isInvalid()
? TypeError()
: Actions.ActOnTemplateIdType(
getCurScope(), ElaboratedTypeKeyword::None,
/*ElaboratedKeywordLoc=*/SourceLocation(), SS,
TemplateId->TemplateKWLoc, TemplateId->Template,
TemplateId->Name, TemplateId->TemplateNameLoc,
TemplateId->LAngleLoc, TemplateArgsPtr, TemplateId->RAngleLoc,
/*IsCtorOrDtorName=*/false, /*IsClassName=*/false,
ImplicitTypenameContext::No);
Comment on lines +1195 to +1201
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@mizvekov mizvekov Jan 28, 2026

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This needs rewiring for nested name and elaborated keyword support, with additional tests covering those cases.

AST dump tests and ast-print roundtrip tests would make good confirmation this works.


if (Ty.isInvalid()) {
DS.SetTypeSpecError();
return TemplateId->RAngleLoc;
}
Type = Ty;
ConsumeAnnotationToken();
} else {
ParsedType Ty = Actions.getTypeName(*Tok.getIdentifierInfo(),
Tok.getLocation(), getCurScope());
if (!Ty) {
DS.SetTypeSpecError();
return Tok.getEndLoc();
}
Type = Ty;
StartLoc = ConsumeToken();
}
EllipsisLoc = ConsumeToken();
BalancedDelimiterTracker T(*this, tok::l_square);
T.consumeOpen();
Expand Down
31 changes: 31 additions & 0 deletions clang/lib/Parse/ParseExprCXX.cpp
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Expand Up @@ -324,6 +324,37 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
continue;
}

// Handle template-id pack-index-specifier
if (Tok.is(tok::annot_template_id) && NextToken().is(tok::ellipsis) &&
GetLookAheadToken(2).is(tok::l_square) &&
!GetLookAheadToken(3).is(tok::r_square)) {
SourceLocation Start = Tok.getLocation();
DeclSpec DS(AttrFactory);
SourceLocation CCLoc;
SourceLocation EndLoc = ParsePackIndexingType(DS);
if (DS.getTypeSpecType() == DeclSpec::TST_error)
return false;

QualType Pattern = Sema::GetTypeFromParser(DS.getRepAsType());
QualType Type =
Actions.ActOnPackIndexingType(Pattern, DS.getPackIndexingExpr(),
DS.getBeginLoc(), DS.getEllipsisLoc());

if (Type.isNull())
return false;

if (!TryConsumeToken(tok::coloncolon, CCLoc)) {
AnnotateExistingIndexedTypeNamePack(ParsedType::make(Type), Start,
EndLoc);
return false;
}
if (Actions.ActOnCXXNestedNameSpecifierIndexedPack(SS, DS, CCLoc,
std::move(Type)))
SS.SetInvalid(SourceRange(Start, CCLoc));
HasScopeSpecifier = true;
continue;
}

if (Tok.is(tok::annot_template_id) && NextToken().is(tok::coloncolon)) {
// We have
//
Expand Down
27 changes: 27 additions & 0 deletions clang/test/Parser/cxx2c-pack-indexing.cpp
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Expand Up @@ -83,3 +83,30 @@ void foo() {
}

}

namespace TemplateIdPackIndexing {

template <typename T>
struct Inner {
using type = T;
static constexpr int value = 42;
};

template <template<typename> typename... TT>
struct Test {
using type = TT<int>...[0]::type;
static constexpr auto value = TT<int>...[0]::value;
};

static_assert(Test<Inner>::value == 42);

template <template<typename> typename... TT>
struct Test2 {
template <typename U>
using type = typename TT<U>...[0]::template rebind<U>;
};

template <template<typename> typename... TT, typename U>
auto test_unannotated() -> typename TT<U>...[0]::type;

}