Cancellable: fix leaking cancellation token

docs/release-notes/.FSharp.Compiler.Service/9.0.300.md

@@ -7,6 +7,7 @@
 * Fix missing nullness warning when static upcast dropped nullness ([Issue #18232](https://github.com/dotnet/fsharp/issues/18232), [PR #18261](https://github.com/dotnet/fsharp/pull/18261))
 * Cancellable: only cancel on OCE with own token ([PR #18277](https://github.com/dotnet/fsharp/pull/18277))
 * Cancellable: set token in more places ([PR #18283](https://github.com/dotnet/fsharp/pull/18283))
+* Cancellable: fix leaking cancellation token ([PR #18295](https://github.com/dotnet/fsharp/pull/18295))
 * Fix NRE when accessing nullable fields of types within their equals/hash/compare methods ([PR #18296](https://github.com/dotnet/fsharp/pull/18296))
 
 ### Added

src/Compiler/Driver/CompilerImports.fs

@@ -2255,7 +2255,6 @@ and [<Sealed>] TcImports
             r: AssemblyResolution
         ) : Async<(_ * (unit -> AvailableImportedAssembly list)) option> =
         async {
-            do! Cancellable.UseToken()
             CheckDisposed()
             let m = r.originalReference.Range
             let fileName = r.resolvedPath
@@ -2327,7 +2326,6 @@ and [<Sealed>] TcImports
         async {
             CheckDisposed()
 
-
             let tcConfig = tcConfigP.Get ctok
 
             let runMethod =

src/Compiler/Service/BackgroundCompiler.fs

@@ -500,11 +500,11 @@ type internal BackgroundCompiler
         }
 
     let getOrCreateBuilder (options, userOpName) : Async<IncrementalBuilder option * FSharpDiagnostic[]> =
-        match tryGetBuilder options with
-        | Some getBuilder ->
-            async {
-                do! Cancellable.UseToken()
+        async {
+            use! _holder = Cancellable.UseToken()
 
+            match tryGetBuilder options with
+            | Some getBuilder ->
                 match! getBuilder with
                 | builderOpt, creationDiags when builderOpt.IsNone || not builderOpt.Value.IsReferencesInvalidated ->
                     return builderOpt, creationDiags
@@ -520,8 +520,8 @@ type internal BackgroundCompiler
                             checkFileInProjectCache.RemoveAnySimilar(ltok, key)))
 
                     return! createAndGetBuilder (options, userOpName)
-            }
-        | _ -> createAndGetBuilder (options, userOpName)
+            | _ -> return! createAndGetBuilder (options, userOpName)
+        }
 
     let getSimilarOrCreateBuilder (options, userOpName) =
         match tryGetSimilarBuilder options with

src/Compiler/Service/ServiceAnalysis.fs

@@ -302,7 +302,7 @@ module UnusedOpens =
     /// Async to allow cancellation.
     let getUnusedOpens (checkFileResults: FSharpCheckFileResults, getSourceLineStr: int -> string) : Async<range list> =
         async {
-            do! Cancellable.UseToken()
+            use! _holder = Cancellable.UseToken()
 
             if checkFileResults.OpenDeclarations.Length = 0 then
                 return []

src/Compiler/Service/TransparentCompiler.fs

@@ -1610,6 +1610,8 @@ type internal TransparentCompiler
         caches.ParseAndCheckFileInProject.Get(
             projectSnapshot.FileKeyWithExtraFileSnapshotVersion fileName,
             async {
+                use! _holder = Cancellable.UseToken()
+
                 use _ =
                     Activity.start "ComputeParseAndCheckFileInProject" [| Activity.Tags.fileName, fileName |> Path.GetFileName |> (!!) |]
 
@@ -1861,6 +1863,7 @@ type internal TransparentCompiler
         caches.AssemblyData.Get(
             projectSnapshot.SignatureKey,
             async {
+                use! _holder = Cancellable.UseToken()
 
                 try
 
@@ -1908,6 +1911,7 @@ type internal TransparentCompiler
         caches.ParseAndCheckProject.Get(
             projectSnapshot.FullKey,
             async {
+                use! _holder = Cancellable.UseToken()
 
                 match! ComputeBootstrapInfo projectSnapshot with
                 | None, creationDiags ->
@@ -1980,6 +1984,8 @@ type internal TransparentCompiler
 
     let tryGetSink (fileName: string) (projectSnapshot: ProjectSnapshot) =
         async {
+            use! _holder = Cancellable.UseToken()
+
             match! ComputeBootstrapInfo projectSnapshot with
             | None, _ -> return None
             | Some bootstrapInfo, _creationDiags ->

src/Compiler/Utilities/Cancellable.fs

@@ -21,7 +21,7 @@ type Cancellable =
     static member UseToken() =
         async {
             let! ct = Async.CancellationToken
-            tokenHolder.Value <- ValueSome ct
+            return Cancellable.UsingToken ct
         }
 
     static member UsingToken(ct) =

src/Compiler/Utilities/Cancellable.fsi

@@ -5,7 +5,7 @@ open System.Threading
 
 [<Sealed>]
 type Cancellable =
-    static member internal UseToken: unit -> Async<unit>
+    static member internal UseToken: unit -> Async<IDisposable>
 
     /// For use in testing only. Cancellable.token should be set only by the cancellable computation.
     static member internal UsingToken: CancellationToken -> IDisposable