Test for clearing state on non-const method (independent of accessors)

Also fix a warning about copies in for-each loop.

Author: jvoung

clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp

@@ -603,7 +603,7 @@ void handleNonConstMemberCall(const CallExpr *CE,
                               LatticeTransferState &State) {
   // When a non-const member function is called, reset some state.
   if (RecordLoc != nullptr) {
-    for (const auto [Field, FieldLoc] : RecordLoc->children()) {
+    for (const auto& [Field, FieldLoc] : RecordLoc->children()) {
       if (isSupportedOptionalType(Field->getType())) {
         auto *FieldRecordLoc = cast_or_null<RecordStorageLocation>(FieldLoc);
         if (FieldRecordLoc) {

clang/unittests/Analysis/FlowSensitive/UncheckedOptionalAccessModelTest.cpp

@@ -2167,6 +2167,26 @@ TEST_P(UncheckedOptionalAccessTest, OptionalReturnedFromFuntionCall) {
   )");
 }
 
+TEST_P(UncheckedOptionalAccessTest, OptionalFieldModified) {
+  ExpectDiagnosticsFor(
+      R"(
+    #include "unchecked_optional_access_test.h"
+
+    struct Foo {
+      $ns::$optional<std::string> opt;
+      void clear();  // assume this may modify the opt field's state
+    };
+
+    void target(Foo& foo) {
+      if (foo.opt) {
+        foo.opt.value();
+        foo.clear();
+        foo.opt.value();  // [[unsafe]]
+      }
+    }
+  )");
+}
+
 TEST_P(UncheckedOptionalAccessTest, StdSwap) {
   ExpectDiagnosticsFor(
       R"(