[clang] [analyzer] Fix [[clang::suppress]] for tricky template specializations (PR #178441)

[Balázs Benics via cfe-commits]

================
@@ -165,6 +165,57 @@ bool BugSuppression::isSuppressed(const BugReport &R) {
          isSuppressed(UniqueingLocation, DeclWithIssue, {});
 }
 
+// For template specializations, returns the primary template definition or
+// partial specialization that was used to instantiate the specialization.
+// This ensures suppression attributes on templates apply to their
+// specializations.
+//
+// For example, given:
+//   template <typename T> class [[clang::suppress]] Wrapper { ... };
+//   Wrapper<int> w; // instantiates ClassTemplateSpecializationDecl
+//
+// When analyzing code in Wrapper<int>, this function maps the specialization
+// back to the primary template definition, allowing us to find the suppression
+// attribute.
+//
+// The function handles two cases:
+// 1. Instantiation from a class template - searches redeclarations to find
+//    the definition (not just a forward declaration).
+// 2. Instantiation from a partial specialization - returns it directly.
+//
+// For non-template-specialization decls, returns the input unchanged.
+static const Decl *
+preferTemplateDefinitionForTemplateSpecializations(const Decl *D) {
+  const auto *SpecializationDecl = dyn_cast<ClassTemplateSpecializationDecl>(D);
+  if (!SpecializationDecl)
+    return D;
+
+  auto InstantiatedFrom = SpecializationDecl->getInstantiatedFrom();
+  if (!InstantiatedFrom)
+    return D;
+
+  // This might be a class template.
+  if (const auto *Tmpl = InstantiatedFrom.dyn_cast<ClassTemplateDecl *>()) {
+    // Interestingly, the source template might be a forward declaration, so we
+    // need to find the definition redeclaration.
+    for (const auto *Redecl : Tmpl->redecls()) {
+      if (cast<ClassTemplateDecl>(Redecl)->isThisDeclarationADefinition()) {
+        return Redecl;
+      }
+    }
+    assert(false && "A redecl must be a definition");
----------------
steakhal wrote:

Applied in abfe124140d29f3d30bc40a9cf155a4b4158ac21

https://github.com/llvm/llvm-project/pull/178441