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[Clang] Don't form a type constraint if the concept is invalid #122065

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Jan 8, 2025
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[Clang] Don't form a type constraint if the concept is invalid #122065

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3127761
[Clang] Don't form a type constraint if the concept is invalid
zyn0217 Jan 8, 2025
2021962
Fix the serialization for invalid constraints
zyn0217 Jan 8, 2025
6b59c7a
fixup! Fix the serialization for invalid constraints
zyn0217 Jan 8, 2025
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3 changes: 3 additions & 0 deletions clang/lib/Sema/SemaTemplate.cpp
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Expand Up @@ -4557,6 +4557,9 @@ Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
const TemplateArgumentListInfo *TemplateArgs) {
assert(NamedConcept && "A concept template id without a template?");

if (NamedConcept->isInvalidDecl())
return ExprError();

llvm::SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
if (CheckTemplateArgumentList(
NamedConcept, ConceptNameInfo.getLoc(),
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3 changes: 2 additions & 1 deletion clang/lib/Serialization/ASTReaderDecl.cpp
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Expand Up @@ -2663,7 +2663,8 @@ void ASTDeclReader::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {

D->setDeclaredWithTypename(Record.readInt());

if (D->hasTypeConstraint()) {
bool TypeConstraintInitialized = D->hasTypeConstraint() && Record.readBool();
if (TypeConstraintInitialized) {
ConceptReference *CR = nullptr;
if (Record.readBool())
CR = Record.readConceptReference();
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5 changes: 3 additions & 2 deletions clang/lib/Serialization/ASTWriterDecl.cpp
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Expand Up @@ -1951,7 +1951,8 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
Record.push_back(D->wasDeclaredWithTypename());

const TypeConstraint *TC = D->getTypeConstraint();
assert((bool)TC == D->hasTypeConstraint());
if (D->hasTypeConstraint())
Record.push_back(/*TypeConstraintInitialized=*/TC != nullptr);
if (TC) {
auto *CR = TC->getConceptReference();
Record.push_back(CR != nullptr);
Expand All @@ -1969,7 +1970,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
if (OwnsDefaultArg)
Record.AddTemplateArgumentLoc(D->getDefaultArgument());

if (!TC && !OwnsDefaultArg &&
if (!D->hasTypeConstraint() && !OwnsDefaultArg &&
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The logic here is a little tricky. The new condition is really "it has a constraint and it does not matter if it is initialized".

I feel like this deserves a comment.

It also makes me wonder if "initialized" is the right word here, isn't it really that it was invalid?

I am just thinking of folks coming to maintain this code in the future and understanding the intent and I don't think the intent is 💯 clear as written.

D->getDeclContext() == D->getLexicalDeclContext() &&
!D->isInvalidDecl() && !D->hasAttrs() &&
!D->isTopLevelDeclInObjCContainer() && !D->isImplicit() &&
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12 changes: 12 additions & 0 deletions clang/test/SemaTemplate/concepts.cpp
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Expand Up @@ -1165,3 +1165,15 @@ concept C = invalid; // expected-error {{use of undeclared identifier 'invalid'}
bool val2 = C<int>;

} // namespace GH109780

namespace GH121980 {

template <class>
concept has_member_difference_type; // expected-error {{expected '='}}

template <has_member_difference_type> struct incrementable_traits; // expected-note {{declared here}}

template <has_member_difference_type Tp>
struct incrementable_traits<Tp>; // expected-error {{not more specialized than the primary}}

}
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