Fix diagnostics cancellation interrupt race

NEWS.md

@@ -1,5 +1,7 @@
 # languageserver 0.3.18
 
+- Retire persistent `callr` workers when cancelling tasks so a late interrupt
+  cannot leak into the next diagnostics run.
 - Add preferred quick fixes for common `lintr` diagnostics and a conflict-aware
   `source.fixAll` action, while making multi-line `nolint` actions apply to every
   affected line.

R/task.R

@@ -90,9 +90,11 @@ Task <- R6::R6Class("Task",
             private$cancelled <- TRUE
             if (!is.null(private$session)) {
                 if (!identical(Sys.getenv("R_COVR"), "true")) {
-                    # Do not close the session, it is persistent and managed by TaskManager.
-                    # Just try to interrupt the ongoing computation.
-                    private$session$interrupt()
+                    # An interrupt can arrive after this call has completed and
+                    # interrupt the next task on the persistent session. Retire
+                    # the worker instead so cancellation cannot leak across tasks.
+                    private$session$kill(
+                        grace = 0, close_connections = FALSE)
                 }
             } else if (!is.null(private$process) && private$process$is_alive()) {
                 if (identical(Sys.getenv("R_COVR"), "true")) {

tests/testthat/test-task.R

@@ -158,6 +158,32 @@ test_that("TaskManager refreshes pending task recency", {
     tm$stop()
 })
 
+test_that("Task cancellation retires its persistent session", {
+    withr::local_envvar(R_COVR = "false")
+    state <- "idle"
+    killed <- FALSE
+    interrupted <- FALSE
+    session <- list(
+        call = function(...) state <<- "busy",
+        get_state = function() state,
+        read = function() NULL,
+        kill = function(grace, close_connections) {
+            expect_equal(grace, 0)
+            expect_false(close_connections)
+            killed <<- TRUE
+            state <<- "finished"
+        },
+        interrupt = function() interrupted <<- TRUE
+    )
+    task <- create_task(function() NULL, list())
+
+    task$start(session)
+    task$kill()
+
+    expect_true(killed)
+    expect_false(interrupted)
+})
+
 test_that("TaskManager does not overprovision while a session starts", {
     tm <- TaskManager$new(
         "starting", use_session = TRUE, min_idle_sessions = 0,