always catch internal cancellations

Author: majocha

src/Compiler/Utilities/Cancellable.fs

@@ -157,8 +157,9 @@ type CancellableBuilder() =
                     match Cancellable.run ct comp with
                     | ValueOrCancelled.Value res -> ValueOrCancelled.Value(Choice1Of2 res)
                     | ValueOrCancelled.Cancelled exn -> ValueOrCancelled.Cancelled exn
-                with err ->
-                    ValueOrCancelled.Value(Choice2Of2 err)
+                with
+                | :? OperationCanceledException as exn when ct.IsCancellationRequested -> ValueOrCancelled.Cancelled exn
+                | err -> ValueOrCancelled.Value(Choice2Of2 err)
 
             match compRes with
             | ValueOrCancelled.Value res ->
@@ -179,8 +180,9 @@ type CancellableBuilder() =
                     match Cancellable.run ct body with
                     | ValueOrCancelled.Value res -> ValueOrCancelled.Value(Choice1Of2 res)
                     | ValueOrCancelled.Cancelled exn -> ValueOrCancelled.Cancelled exn
-                with err ->
-                    ValueOrCancelled.Value(Choice2Of2 err)
+                with
+                | :? OperationCanceledException as exn when ct.IsCancellationRequested -> ValueOrCancelled.Cancelled exn
+                | err -> ValueOrCancelled.Value(Choice2Of2 err)
 
             match compRes with
             | ValueOrCancelled.Value res ->
@@ -201,8 +203,9 @@ type CancellableBuilder() =
                     match Cancellable.run ct comp with
                     | ValueOrCancelled.Value res -> ValueOrCancelled.Value(Choice1Of2 res)
                     | ValueOrCancelled.Cancelled exn -> ValueOrCancelled.Cancelled exn
-                with err ->
-                    ValueOrCancelled.Value(Choice2Of2 err)
+                with
+                | :? OperationCanceledException as exn when ct.IsCancellationRequested -> ValueOrCancelled.Cancelled exn
+                | err -> ValueOrCancelled.Value(Choice2Of2 err)
 
             match compRes with
             | ValueOrCancelled.Value res ->