[clang] [LifetimeSafety] Avoid suggesting lifetimebound attribute on primary templates declarations (PR #203866)

[via cfe-commits]

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@@ -82,6 +82,39 @@ class LifetimeChecker {
     llvm_unreachable("unhandled causing fact in PointerUnion");
   }
 
+  /// For an explicit specialization, returns the source-level specialization
+  /// declaration to target for attribute placement, if one exists. Skips
+  /// implicit specialization redeclarations that are backed by the template
+  /// pattern. In other cases, returns nullptr.
+  static const FunctionDecl *
+  getExplicitSpecializationDeclForAttr(const FunctionDecl *FDef) {
+    if (FDef->getTemplateSpecializationKindForInstantiation() !=
+        TSK_ExplicitSpecialization)
+      return nullptr;
+
+    auto IsImplicitTemplateSpecialization = [](const FunctionDecl *Redecl,
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NeKon69 wrote:

Well, as far as can I see, there is no reliable way to distinguish between clang-generated instantiations and user written ones, that is mostly because they both fall under the same `TSK_ExplicitSpecialization` category..

https://github.com/llvm/llvm-project/pull/203866