Lin: Print commands that trigger unexpected exceptions

CHANGES.md

@@ -1,5 +1,11 @@
 # Changes
 
+## Next version
+
+- #324: When a command causes an unexpectedly uncaught exception,
+        display that command along with the exception itself in both
+        `Lin` and `STM`
+
 ## 0.2
 
 - #342: Add two submodules of combinators in `Util`:

lib/STM.ml

@@ -170,15 +170,15 @@ struct
     let rec interp_agree s sut cs = match cs with
       | [] -> true
       | c::cs ->
-        let res = Spec.run c sut in
+        let res = try Spec.run c sut with e -> Util.wrap_uncaught_exn Spec.show_cmd c e in
         let b   = Spec.postcond c s res in
         let s'  = Spec.next_state c s in
         b && interp_agree s' sut cs
 
     let rec check_disagree s sut cs = match cs with
       | [] -> None
       | c::cs ->
-        let res = Spec.run c sut in
+        let res = try Spec.run c sut with e -> Util.wrap_uncaught_exn Spec.show_cmd c e in
         let b   = Spec.postcond c s res in
         let s'  = Spec.next_state c s in
         if b

lib/lin.ml

@@ -479,6 +479,8 @@ module MakeCmd (ApiSpec : Spec) : Internal.CmdSpec = struct
       apply_f (f arg) rem state
 
   let run cmd state =
-    let Cmd { args ; rty ; f ; _ } = cmd in
-    Res (rty, apply_f f args state)
+    try
+      let (Cmd { args; rty; f; _ }) = cmd in
+      Res (rty, apply_f f args state)
+    with e -> Util.wrap_uncaught_exn show_cmd cmd e
 end

lib/util.ml

@@ -75,6 +75,23 @@ let protect (f : 'a -> 'b) (a : 'a) : ('b, exn) result =
   try Result.Ok (f a)
   with e -> Result.Error e
 
+exception Uncaught_exception of string * exn
+
+let print_uncaught_exception e =
+  match e with
+  | Uncaught_exception (cmd, exc) ->
+      Some
+        (Format.sprintf "%s raised but not caught while running %s"
+           (Printexc.to_string exc) cmd)
+  | _ -> None
+
+let _ =
+  Printexc.register_printer print_uncaught_exception
+
+let wrap_uncaught_exn show x e =
+  let bt = Printexc.get_raw_backtrace () in
+  Printexc.raise_with_backtrace (Uncaught_exception (show x, e)) bt
+
 module Pp = struct
   open Format
 

lib/util.mli

@@ -41,6 +41,20 @@ val print_triple_vertical :
 val protect : ('a -> 'b) -> 'a -> ('b, exn) result
 (** [protect f] turns an [exception] throwing function into a [result] returning function. *)
 
+exception Uncaught_exception of string * exn
+(** [Uncaught_exception (cmd, exc)] is used to signal that the
+    exception [exc] was not caught (but should have been) during the
+    execution of [cmd]. That exception will be printed as:
+    ["... raised but not caught while running " ^ cmd]. *)
+
+val wrap_uncaught_exn : ('a -> string) -> 'a -> exn -> 'b
+(** [wrap_uncaught_exn show x e] wraps the exception [e] into an
+    [Uncaught_exception] with the command as pretty-printed by
+    [show x] and raises that [Uncaught_exception].
+    [wrap_uncaught_exn] preserves the current backtrace so it
+    must be called from the exception handler, like so:
+    [try ... with e -> wrap_uncaught_exn show x e] *)
+
 module Pp : sig
   (** Pretty-printing combinators that generate valid OCaml syntax for common
       types along with combinators for user-defined types *)

test/dune

@@ -54,3 +54,30 @@
  (libraries qcheck-stm.sequential threads.posix)
  (action
   (with-accepted-exit-codes 1 (run ./%{test} --verbose --seed 229109553))))
+
+(test
+ (name uncaught_lin)
+ (package qcheck-lin)
+ (modules uncaught_lin)
+ (libraries qcheck-lin.domain)
+ (enabled_if (>= %{ocaml_version} 5))
+ (action
+  (pipe-outputs
+   (with-accepted-exit-codes 1
+    (run %{test} --no-colors --verbose --seed 260395858))
+   ; filter out output that is not deterministic enough across
+   ; versions and platforms
+   (run sed -e "/^[[]/d" -e "s/ ([0-9]* shrink steps)//"))))
+
+(test
+ (name uncaught_stm)
+ (package qcheck-stm)
+ (modules uncaught_stm)
+ (libraries qcheck-stm.sequential)
+ (action
+  (pipe-outputs
+   (with-accepted-exit-codes 1
+    (run %{test} --no-colors --verbose --seed 260395858))
+   ; filter out output that is not deterministic enough across
+   ; versions and platforms
+   (run sed -e "/^[[]/d" -e "s/ ([0-9]* shrink steps)//"))))

test/uncaught_lin.expected

@@ -0,0 +1,32 @@
+random seed: 260395858
+generated error fail pass / total     time test name
+
+=== Error ======================================================================
+
+Test Lin DSL test of uncaught exceptions errored on:
+
+                           |             
+                     always_fail t       
+                           |             
+                .---------------------.
+                |                     |             
+
+
+exception Failure("unexpected") raised but not caught while running always_fail t
+
+
+=== Error ======================================================================
+
+Test neg Lin DSL test of uncaught exceptions errored on:
+
+                           |             
+                     always_fail t       
+                           |             
+                .---------------------.
+                |                     |             
+
+
+exception Failure("unexpected") raised but not caught while running always_fail t
+
+================================================================================
+failure (0 tests failed, 2 tests errored, ran 2 tests)

test/uncaught_lin.ml

@@ -0,0 +1,24 @@
+(* Test of the behaviour of Lin tests with uncaught exceptions *)
+
+let always_fail () = failwith "unexpected"
+
+module UncaughtExcConf = struct
+  open Lin
+
+  type t = unit
+
+  let init () = ()
+  let cleanup _ = ()
+  let api = [ val_ "always_fail" always_fail (t @-> returning unit) ]
+end
+
+module UncaughtExc_domain = Lin_domain.Make (UncaughtExcConf)
+
+let _ =
+  QCheck_base_runner.run_tests_main
+    [
+      UncaughtExc_domain.lin_test ~count:10
+        ~name:"Lin DSL test of uncaught exceptions";
+      UncaughtExc_domain.neg_lin_test ~count:10
+        ~name:"neg Lin DSL test of uncaught exceptions";
+    ]

test/uncaught_stm.expected

@@ -0,0 +1,24 @@
+random seed: 260395858
+generated error fail pass / total     time test name
+
+=== Error ======================================================================
+
+Test STM test of uncaught exceptions errored on:
+
+   AlwaysFail ()
+
+
+exception Failure("unexpected") raised but not caught while running AlwaysFail ()
+
+
+=== Error ======================================================================
+
+Test neg STM test of uncaught exceptions errored on:
+
+   AlwaysFail ()
+
+
+exception Failure("unexpected") raised but not caught while running AlwaysFail ()
+
+================================================================================
+failure (0 tests failed, 2 tests errored, ran 2 tests)

test/uncaught_stm.ml

@@ -0,0 +1,32 @@
+(* Test of the behaviour of STM tests with uncaught exceptions *)
+
+let always_fail () = failwith "unexpected"
+
+module UncaughtExcConf : STM.Spec = struct
+  open STM
+
+  type sut = unit
+  type state = unit
+  type cmd = AlwaysFail of sut
+
+  let show_cmd = function AlwaysFail () -> "AlwaysFail ()"
+  let arb_cmd _ = QCheck.(make ~print:show_cmd (Gen.pure (AlwaysFail ())))
+  let init_state = ()
+  let next_state _ _ = ()
+  let init_sut _ = ()
+  let cleanup _ = ()
+  let precond _ _ = true
+  let run c s = match c with AlwaysFail () -> Res (unit, always_fail s)
+
+  let postcond c _ r =
+    match (c, r) with AlwaysFail (), Res ((Unit, _), _) -> true | _ -> false
+end
+
+module UE = STM_sequential.Make (UncaughtExcConf)
+
+let _ =
+  QCheck_base_runner.run_tests_main
+    [
+      UE.agree_test ~count:10 ~name:"STM test of uncaught exceptions";
+      UE.neg_agree_test ~count:10 ~name:"neg STM test of uncaught exceptions";
+    ]