[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;
+
+  // Iterate through builtin function format attributes. Then check
+  // if parent function has these attributes. If parent function does
+  // not have builtin function format attribut, emit warning.
----------------
aaronpuchert wrote:

This seems to be missing an important ingredient, unless I'm overlooking it: we only want to diagnose if the format string and the var args are forwarded. Simply calling one of these functions does not mean that we need to propagate the attribute, e.g. if we're calling it with a string literal.

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