Make `absl::StatusOr::AssignStatus` public. Recommend against using it outside…

Make `absl::StatusOr::AssignStatus` public. Recommend against using it outside of generic programming (attempt #2 after internal fix)

PiperOrigin-RevId: 529796927
Change-Id: I755b7d907f96f4a05d01620503bf0862ce35e847

absl/status/statusor.h

@@ -612,6 +612,21 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
     return this->data_;
   }
 
+  // StatusOr<T>::AssignStatus()
+  //
+  // Sets the status of `absl::StatusOr<T>` to the given non-ok status value.
+  //
+  // NOTE: We recommend using the constructor and `operator=` where possible.
+  // This method is intended for use in generic programming, to enable setting
+  // the status of a `StatusOr<T>` when `T` may be `Status`. In that case, the
+  // constructor and `operator=` would assign into the inner value of type
+  // `Status`, rather than status of the `StatusOr` (b/280392796).
+  //
+  // REQUIRES: !Status(std::forward<U>(v)).ok(). This requirement is DCHECKed.
+  // In optimized builds, passing absl::OkStatus() here will have the effect
+  // of passing absl::StatusCode::kInternal as a fallback.
+  using internal_statusor::StatusOrData<T>::AssignStatus;
+
  private:
   using internal_statusor::StatusOrData<T>::Assign;
   template <typename U>

absl/status/statusor_test.cc

@@ -1844,4 +1844,37 @@ TEST(StatusOr, AssignmentFromTypeConvertibleToStatus) {
   }
 }
 
+TEST(StatusOr, StatusAssignmentFromStatusError) {
+  absl::StatusOr<absl::Status> statusor;
+  statusor.AssignStatus(absl::CancelledError());
+
+  EXPECT_FALSE(statusor.ok());
+  EXPECT_EQ(statusor.status(), absl::CancelledError());
+}
+
+#if GTEST_HAS_DEATH_TEST
+TEST(StatusOr, StatusAssignmentFromStatusOk) {
+  EXPECT_DEBUG_DEATH(
+      {
+        absl::StatusOr<absl::Status> statusor;
+        // This will DCHECK.
+        statusor.AssignStatus(absl::OkStatus());
+        // In optimized mode, we are actually going to get error::INTERNAL for
+        // status here, rather than crashing, so check that.
+        EXPECT_FALSE(statusor.ok());
+        EXPECT_EQ(statusor.status().code(), absl::StatusCode::kInternal);
+      },
+      "An OK status is not a valid constructor argument to StatusOr<T>");
+}
+#endif
+
+TEST(StatusOr, StatusAssignmentFromTypeConvertibleToStatus) {
+  CustomType<MyType, kConvToStatus> v;
+  absl::StatusOr<MyType> statusor;
+  statusor.AssignStatus(v);
+
+  EXPECT_FALSE(statusor.ok());
+  EXPECT_EQ(statusor.status(), static_cast<absl::Status>(v));
+}
+
 }  // namespace