[main_random]: take an optional parameter [timeout]; return number of discovered failures.

src/Engine.ml

@@ -1419,8 +1419,8 @@ let log scenario fuel =
 
 (* -------------------------------------------------------------------------- *)
 
-(* [main_random_loop prologue clock fuel] performs an unbounded number of test
-   runs in random mode. *)
+(* [main_random_loop prologue clock fuel accu] performs an unbounded number of
+   test runs in random mode. *)
 
 (* While the tests run, we print information roughly every second. We print
    how many tests have been performed so far, our overall average speed, and
@@ -1435,7 +1435,14 @@ let log scenario fuel =
 (* For each value of [fuel], we use an explicit infinite loop to perform an
    unbounded number of runs. *)
 
-let rec main_random_loop prologue clock fuel =
+(* If the clock [clock] has no time limit, then [main_random_loop] never
+   terminates. If this clock has a time limit then [main_random_loop]
+   terminates once the time limit has been reached, and it returns the number
+   of failure scenarios that have been discovered and logged along the way.
+   The accumulator [accu] records the number of failure scenarios discovered
+   so far. *)
+
+let rec main_random_loop prologue clock fuel (accu : int) : int =
   try
     (* An infinite loop. *)
     while true do
@@ -1443,14 +1450,19 @@ let rec main_random_loop prologue clock fuel =
       run prologue fuel;
       (* Tick the clock and, once in a while, display statistics. *)
       tick clock fuel
-    done
-  with Abort (scenario, fuel) ->
-    log scenario fuel;
-    (* We have been able to find a problem with a certain amount of
-       fuel. Try again, with this amount. This restricts our search
-       space, and (with luck) we might now be able to find an even
-       shorter scenario. *)
-    main_random_loop prologue clock fuel
+    done;
+    (* This cannot happen. *)
+    assert false
+  with
+  | Abort (scenario, fuel) ->
+      log scenario fuel;
+      (* We have been able to find a problem with a certain amount of
+         fuel. Try again, with this amount. This restricts our search
+         space, and (with luck) we might now be able to find an even
+         shorter scenario. *)
+      main_random_loop prologue clock fuel (accu + 1)
+  | Clock.Timeout ->
+      accu
 
 (* [main_random prologue fuel] performs an unbounded number of test
    runs in random mode. *)
@@ -1464,12 +1476,12 @@ let rec main_random_loop prologue clock fuel =
    The main reason for this change is to allow imposing a time limit
    on the whole process. *)
 
-let main_random prologue fuel =
+let main_random ?timeout prologue fuel : int =
   let source = None in
   Gen.with_source source @@ fun () ->
   let granularity = 1000 in
-  let clock = Clock.make granularity in
-  main_random_loop prologue clock fuel
+  let clock = Clock.make ?timeout granularity in
+  main_random_loop prologue clock fuel 0
 
 (* -------------------------------------------------------------------------- *)
 
@@ -1505,4 +1517,5 @@ let main ?prologue:(prologue=none) fuel =
   | Some _ ->
       main_afl source prologue fuel
   | None ->
-      main_random prologue fuel
+      let (failures : int) = main_random prologue fuel in
+      ignore failures