[clang] [-Wunsafe-buffer-usage] Add FixableGadget for AddAssign in UnspecifiedUntypedContext (PR #71862)

[Artem Dergachev via cfe-commits]

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@@ -1312,21 +1353,29 @@ PointerInitGadget::getFixits(const Strategy &S) const {
   return std::nullopt;
 }
 
+static bool isNonNegativeIntegerExpr(const Expr *Expr, const VarDecl *VD,
+                                     const ASTContext &Ctx) {
+  if (auto ConstVal = Expr->getIntegerConstantExpr(Ctx)) {
+    if (ConstVal->isNegative())
+      return false;
+  } else if (!Expr->getType()->isUnsignedIntegerType())
+    return false;
+  return true;
+}
+
 std::optional<FixItList>
 ULCArraySubscriptGadget::getFixits(const Strategy &S) const {
   if (const auto *DRE =
           dyn_cast<DeclRefExpr>(Node->getBase()->IgnoreImpCasts()))
     if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
       switch (S.lookup(VD)) {
       case Strategy::Kind::Span: {
+        
         // If the index has a negative constant value, we give up as no valid
         // fix-it can be generated:
         const ASTContext &Ctx = // FIXME: we need ASTContext to be passed in!
             VD->getASTContext();
-        if (auto ConstVal = Node->getIdx()->getIntegerConstantExpr(Ctx)) {
-          if (ConstVal->isNegative())
-            return std::nullopt;
-        } else if (!Node->getIdx()->getType()->isUnsignedIntegerType())
+        if (!isNonNegativeIntegerExpr(Node->getIdx(), VD, Ctx))
----------------
haoNoQ wrote:

I'm starting to like how these checks live in `getFixits()`, as opposed to the matcher. It's not like we'll ever be able to fix the signed case, but this way they'll show up in debug statistics as "gadget refused to produce a fix", which is better than the generic "it never matched". We could even make a dedicated debug message for this failure specifically!

https://github.com/llvm/llvm-project/pull/71862