report cycles with slight overlap as before

Signed-off-by: Arseniy Alekseyev <aalekseyev@janestreet.com>

src/dag/dag.ml

@@ -78,7 +78,11 @@ module Make(Value : Value) : S with type value := Value.t = struct
     match IC.add_edge_or_detect_cycle g v w with
     | IC.EdgeAdded -> ()
     | IC.EdgeCreatesCycle compute_cycle ->
-      raise (Cycle (List.rev (compute_cycle ())))
+      raise (Cycle (
+        let path = (compute_cycle ()) in
+        assert (List.hd path == w);
+        assert (Option.value_exn (List.last path) == v);
+        List.rev path @ [ v ]))
 
   let children node = node.info.deps
 

test/blackbox-tests/test-cases/loop/run.t

@@ -13,16 +13,16 @@ does show a cycle.
 
   $ dune build --display short result1
   Dependency cycle between the following files:
-      _build/default/input
-  --> _build/default/result2
+      _build/default/result2
   --> _build/default/input
+  --> _build/default/result2
   [1]
 
   $ dune build --display short result1 --debug-dependency-path
   Dependency cycle between the following files:
-      _build/default/input
-  --> _build/default/result2
+      _build/default/result2
   --> _build/default/input
+  --> _build/default/result2
   -> required by result2
   -> required by input
   -> required by result1

test/unit-tests/dag.mlt

@@ -101,7 +101,8 @@ val node41 : node = (6: k=1) (child 4 1) []
                                                              ]]]];
                   (2: k=1) (child 1 1) []]
 - : string list option =
-Some ["child 4 1"; "child 3 1"; "child 2 1"; "child 1 2"; "root"]
+Some
+ ["child 4 1"; "child 3 1"; "child 2 1"; "child 1 2"; "root"; "child 4 1"]
 - : node =
 (1: k=2) (root) [(3: k=2) (child 1 2) [(4: k=2) (child 2 1) [(5: k=2) (child 3 1) [
                                                              (6: k=2) (child 4 1) [
@@ -220,11 +221,11 @@ cycle_test `a
 ;;
 
 [%%expect{|
-- : int list = [23; 22; 21; 20; 14; 13; 12; 11]
+- : int list = [23; 22; 21; 20; 14; 13; 12; 11; 23]
 |}]
 ;;
 cycle_test `b
 ;;
 [%%expect{|
-- : int list = [23; 22; 21; 20; 14; 13; 12; 11]
+- : int list = [23; 22; 21; 20; 14; 13; 12; 11; 23]
 |}]

test/unit-tests/memoize.mlt

@@ -168,7 +168,7 @@ with
 !stack |> List.map ~f:(fun st -> Stack_frame.name st, Stack_frame.input st);;
 
 [%%expect{|
-- : int list option = Some [2; 1; 0]
+- : int list option = Some [2; 1; 0; 2]
 - : int = 4
 - : (string * Sexp.t) list =
 [("cycle", Atom "2"); ("cycle", Atom "1"); ("cycle", Atom "0");