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

[Aaron Ballman via cfe-commits]

================
@@ -7096,6 +7096,111 @@ static void handleSwiftAsyncAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     checkSwiftAsyncErrorBlock(S, D, ErrorAttr, AsyncAttr);
 }
 
+// This function is called only if function call is not inside template body.
+// TODO: Add call for function calls inside template body.
+// Check if parent function misses format attribute. If misses, emit warning.
+void Sema::DiagnoseMissingFormatAttributes(const FunctionDecl *FDecl,
+                                           ArrayRef<const Expr *> Args,
+                                           SourceLocation Loc) {
+  assert(FDecl);
+
+  const FunctionDecl *ParentFuncDecl = getCurFunctionDecl();
+  if (!ParentFuncDecl)
+    return;
+
+  // If function is a member of struct/union/class, format attribute argument
+  // indexing starts from 2. Otherwise, it starts from 1.
+  const unsigned int FormatArgumentIndexOffset =
+      isInstanceMethod(FDecl) ? 2 : 1;
+  const unsigned int ParentFunctionFormatArgumentIndexOffset =
+      isInstanceMethod(ParentFuncDecl) ? 2 : 1;
+
+  // Check if function has format attribute with forwarded format string.
+  IdentifierInfo *AttrType;
+  const ParmVarDecl *FormatArg;
+  if (!llvm::any_of(
+          FDecl->specific_attrs<FormatAttr>(), [&](const FormatAttr *Attr) {
+            const int FormatIndexOffseted =
+                Attr->getFormatIdx() - FormatArgumentIndexOffset;
+            if (FormatIndexOffseted < 0 ||
+                (unsigned)FormatIndexOffseted >= Args.size())
+              return false;
+
+            const DeclRefExpr *FormatArgExpr = dyn_cast_or_null<DeclRefExpr>(
+                Args[FormatIndexOffseted]->IgnoreParenCasts());
----------------
AaronBallman wrote:

```suggestion
            const auto *FormatArgExpr = dyn_cast<DeclRefExpr>(
                Args[FormatIndexOffseted]->IgnoreParenCasts());
```
Can drop the `or_null` because we're relying on `Args[FormatIndexOffseted]` to be non-null already.

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