[clang] [clang] Catch missing format attributes (PR #70024)

[Aaron Puchert via cfe-commits]

================
@@ -435,6 +435,86 @@ bool Sema::ConstantFoldAttrArgs(const AttributeCommonInfo &CI,
   return true;
 }
 
+// Warn if parent function does not have builtin function format attribute.
+void Sema::DiagnoseMissingFormatAttributes(NamedDecl *FDecl,
+                                           SourceLocation Loc) {
+  if (!FDecl)
+    return;
+
+  auto *FD = dyn_cast_or_null<FunctionDecl>(FDecl);
+  if (!FD)
+    return;
+
+  unsigned BuiltinID = FD->getBuiltinID(/*ConsiderWrappers=*/true);
+  
+  // Function is not builtin if it's builtin ID is 0.
+  if (!BuiltinID)
+    return;
+
+  // Check if function is one with format attribute.
+  switch (BuiltinID) {
+  case Builtin::BIprintf:
+  case Builtin::BIfprintf:
+  case Builtin::BIsprintf:
+  case Builtin::BIscanf:
+  case Builtin::BIfscanf:
+  case Builtin::BIsscanf:
+  case Builtin::BIvprintf:
+  case Builtin::BIvfprintf:
+  case Builtin::BIvsprintf:
+    break;
+  default: {
+    // In C99 mode check functions below.
+    if (!getLangOpts().C99)
+      return;
+    switch (BuiltinID) {
+    case Builtin::BIsnprintf:
+    case Builtin::BIvsnprintf:
+    case Builtin::BIvscanf:
+    case Builtin::BIvfscanf:
+    case Builtin::BIvsscanf:
+      break;
+    default:
+      return;
+    }
+  }
+  }
+
+  Scope *ParentScope = getCurScope() ? getCurScope()->getFnParent() : nullptr;
+  if (!ParentScope)
+    return;
+
+  DeclContext *ParentScopeEntity = ParentScope->getEntity();
+  if (!ParentScopeEntity)
+    return;
+  if (ParentScopeEntity->getDeclKind() != Decl::Kind::Function)
+    return;
+
+  FunctionDecl *ParentFuncDecl = static_cast<FunctionDecl *>(ParentScopeEntity);
+  if (!ParentFuncDecl)
+    return;
+  if (!ParentFuncDecl->isVariadic())
+    return;
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aaronpuchert wrote:

Couldn't we use `getCurFunctionDecl`?

https://github.com/llvm/llvm-project/pull/70024