GH58368: Correct concept checking in a lambda defined in concept

As that bug reports, the problem here is that the lambda's
'context-decl' was not set to the concept, and the lambda picked up
template arguments from the concept.  SO, we failed to get the correct
template arguments in SemaTemplateInstantiate.

However, a Concept Specialization is NOT a decl, its an expression, so
we weren't able to put the concept in the decl tree like we needed.
This patch introduces a ConceptSpecializationDecl, which is the smallest
type possible to use for this purpose, containing only the template
arguments.

The net memory impliciation of this is turning a
trailing-objects into a pointer to a type with trailing-objects,  so it
should be minor.

As future work, we may consider giving this type more responsibility, or
figuring out how to better merge duplicates, but as this is just a
template-argument collection at the moment, there isn't much value to
it.

Differential Revision: https://reviews.llvm.org/D136451

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTCommon.cpp b/clang/lib/Serialization/ASTCommon.cpp
index 53e4c88..152037d 100644
--- a/clang/lib/Serialization/ASTCommon.cpp
+++ b/clang/lib/Serialization/ASTCommon.cpp
@@ -430,6 +430,7 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::Decomposition:
   case Decl::Binding:
   case Decl::Concept:
+  case Decl::ImplicitConceptSpecialization:
   case Decl::LifetimeExtendedTemporary:
   case Decl::RequiresExprBody:
   case Decl::UnresolvedUsingIfExists: