[clang] [alpha.webkit.UncountedLocalVarsChecker] Warn the use of a raw pointer/reference when the guardian variable gets mutated. (PR #113859)

[Rashmi Mudduluru via cfe-commits]

================
@@ -83,6 +83,77 @@ void foo7(RefCountable* obj) {
   bar.obj->method();
 }
 
+void foo8(RefCountable* obj) {
+  RefPtr<RefCountable> foo;
+  {
+    RefCountable *bar = foo.get();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    foo = nullptr;
+    bar->method();
+  }
+  RefPtr<RefCountable> baz;
+  {
+    RefCountable *bar = baz.get();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    baz = obj;
+    bar->method();
+  }
+  foo = nullptr;
+  {
+    RefCountable *bar = foo.get();
+    // No warning. It's okay to mutate RefPtr in an outer scope.
+    bar->method();
+  }
+  foo = obj;
+  {
+    RefCountable *bar = foo.get();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    foo.releaseNonNull();
+    bar->method();
+  }
+  {
+    RefCountable *bar = foo.get();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    foo = obj ? obj : nullptr;
+    bar->method();
+  }
+}
+
+void foo9(RefCountable& o) {
+  Ref<RefCountable> guardian(o);
+  {
+    RefCountable &bar = guardian.get();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    guardian = o; // We don't detect that we're setting it to the same value.
+    bar.method();
+  }
+  {
+    RefCountable *bar = guardian.ptr();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    Ref<RefCountable> other(*bar); // We don't detect other has the same value as guardian.
+    guardian.swap(other);
+    bar->method();
+  }
+  {
+    RefCountable *bar = guardian.ptr();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    Ref<RefCountable> other(static_cast<Ref<RefCountable>&&>(guardian));
+    bar->method();
+  }
+  {
+    RefCountable *bar = guardian.ptr();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    guardian.leakRef();
+    bar->method();
+  }
+  {
+    RefCountable *bar = guardian.ptr();
+    // expected-warning at -1{{Local variable 'bar' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    guardian = o.trivial() ? o : *bar;
----------------
t-rasmud wrote:

Ah ok, that makes sense. Thank you for the explanation. Can we have a test case where the warning is expected? Maybe the following?
```
{
    RefCountable *bar = foo->trivial()? foo.get() : nullptr;
}
```

https://github.com/llvm/llvm-project/pull/113859