[clang] [alpha.webkit.UnretainedLocalVarsChecker] Treat the collection of a fast enumeration as the origin of its element (PR #230818)

[Balázs Benics via cfe-commits]

================
@@ -574,6 +574,91 @@ void ns() {
 
 }
 
+namespace fast_enumeration {
+
+NSArray *provideArray();
+
+void iterateLocal() {
+  RetainPtr<NSArray> array = provideArray();
+  for (SomeObj *obj in array.get())
+    [obj doWork];
+}
+
+void iterateLocalInNestedScope() {
+  RetainPtr<NSArray> array = provideArray();
+  {
+    for (SomeObj *obj in array.get()) {
+      for (SomeObj *otherObj in array.get())
+        [otherObj doWork];
+      [obj doWork];
+    }
+  }
+}
+
+void iterateLocalWithRangeBasedFor() {
+  RetainPtr<NSArray> array = provideArray();
+  for (SomeObj *obj : array.get())
+    [obj doWork];
+}
+
+void iterateLocalWithId() {
+  RetainPtr<NSArray> array = provideArray();
+  for (id obj in array.get())
+    [obj doWork];
+}
+
+void iterateLocalClearedInBody() {
+  RetainPtr<NSArray> array = provideArray();
+  for (SomeObj *obj in array.get()) {
+    // expected-warning at -1{{Local variable 'obj' is a raw pointer to RetainPtr-capable type 'SomeObj' [alpha.webkit.UnretainedLocalVarsChecker]}}
+    array = nullptr;
+    [obj doWork];
+  }
+}
+
+void iterateLocalClearedAfterLoop() {
+  RetainPtr<NSArray> array = provideArray();
+  for (SomeObj *obj in array.get())
+    [obj doWork];
+  array = nullptr;
+}
+
+void iterateParam(NSArray *array) {
+  for (SomeObj *obj in array)
+    [obj doWork];
+}
+
+void iterateParamReassigned(NSArray *array) {
+  for (SomeObj *obj in array) {
----------------
steakhal wrote:

I don't think this matching works for structured-bindings declaring one or multiple binding decls.
```c++
  for (auto [obj] in array) {
```

https://github.com/llvm/llvm-project/pull/230818