review: add clarification on other join type's swap_inputs()

Author: 2010YOUY01

datafusion/physical-plan/src/joins/cross_join.rs

@@ -192,6 +192,12 @@ impl CrossJoinExec {
     ///
     /// This is not a public API and is for internal use only; see [API policy] for details.
     ///
+    /// Direct use of this API in downstream projects is discouraged because
+    /// correctness depends on strict preconditions. See the notes above for
+    /// correct usage.
+    ///
+    /// This API may change frequently as internal join optimizations evolve.
+    ///
     /// [API policy]: https://datafusion.apache.org/contributor-guide/api-health.html#internal-public-apis
     #[doc(hidden)]
     pub fn swap_inputs(&self) -> Result<Arc<dyn ExecutionPlan>> {

datafusion/physical-plan/src/joins/nested_loop_join.rs

@@ -481,6 +481,12 @@ impl NestedLoopJoinExec {
     ///
     /// This is not a public API and is for internal use only; see [API policy] for details.
     ///
+    /// Direct use of this API in downstream projects is discouraged because
+    /// correctness depends on strict preconditions. See the notes above for
+    /// correct usage.
+    ///
+    /// This API may change frequently as internal join optimizations evolve.
+    ///
     /// [API policy]: https://datafusion.apache.org/contributor-guide/api-health.html#internal-public-apis
     #[doc(hidden)]
     pub fn swap_inputs(&self) -> Result<Arc<dyn ExecutionPlan>> {

datafusion/physical-plan/src/joins/sort_merge_join/exec.rs

@@ -349,6 +349,19 @@ impl SortMergeJoinExec {
     /// This function should be called BEFORE inserting any repartitioning
     /// operators on the join's children. Check [`super::super::HashJoinExec::swap_inputs`]
     /// for more details.
+    ///
+    /// # Public Only for Internal Use:
+    ///
+    /// This is not a public API and is for internal use only; see [API policy] for details.
+    ///
+    /// Direct use of this API in downstream projects is discouraged because
+    /// correctness depends on strict preconditions. See the notes above for
+    /// correct usage.
+    ///
+    /// This API may change frequently as internal join optimizations evolve.
+    ///
+    /// [API policy]: https://datafusion.apache.org/contributor-guide/api-health.html#internal-public-apis
+    #[doc(hidden)]
     pub fn swap_inputs(&self) -> Result<Arc<dyn ExecutionPlan>> {
         let left = self.left();
         let right = self.right();