internal: prepare to store OpQueue results in the queue itself

crates/rust-analyzer/src/op_queue.rs

@@ -1,29 +1,37 @@
-//! Bookkeeping to make sure only one long-running operation is executed.
+//! Bookkeeping to make sure only one long-running operation is being executed
+//! at a time.
 
-pub(crate) struct OpQueue<D> {
-    op_scheduled: Option<D>,
+pub(crate) struct OpQueue<Args, Output> {
+    op_scheduled: Option<Args>,
     op_in_progress: bool,
+    last_op_result: Output,
 }
 
-impl<D> Default for OpQueue<D> {
+impl<Args, Output: Default> Default for OpQueue<Args, Output> {
     fn default() -> Self {
-        Self { op_scheduled: None, op_in_progress: false }
+        Self { op_scheduled: None, op_in_progress: false, last_op_result: Default::default() }
     }
 }
 
-impl<D> OpQueue<D> {
-    pub(crate) fn request_op(&mut self, data: D) {
+impl<Args, Output> OpQueue<Args, Output> {
+    pub(crate) fn request_op(&mut self, data: Args) {
         self.op_scheduled = Some(data);
     }
-    pub(crate) fn should_start_op(&mut self) -> Option<D> {
+    pub(crate) fn should_start_op(&mut self) -> Option<Args> {
         if self.op_in_progress {
             return None;
         }
         self.op_in_progress = self.op_scheduled.is_some();
         self.op_scheduled.take()
     }
-    pub(crate) fn op_completed(&mut self) {
+    pub(crate) fn op_completed(&mut self, result: Output) {
         assert!(self.op_in_progress);
         self.op_in_progress = false;
+        self.last_op_result = result;
+    }
+
+    #[allow(unused)]
+    pub(crate) fn last_op_result(&self) -> &Output {
+        &self.last_op_result
     }
 }