ocaml/libs: List.last and List.head now return options

Previously an exception was raised for last, head is a new function.

Also adds a latest_release to datamodel_types that can't fail after the
module has been loaded. (the list is populated so it won't fail when the
module is loaded either)

Signed-off-by: Pau Ruiz Safont <[email protected]>

Author: psafont

ocaml/idl/datamodel_types.ml

@@ -359,6 +359,9 @@ let release_order_full =
 let release_order =
   List.filter (fun x -> x.code_name <> None) release_order_full
 
+let latest_release =
+  Xapi_stdext_std.Listext.List.last release_order |> Option.get
+
 exception Unknown_release of string
 
 exception UnspecifiedRelease

ocaml/idl/datamodel_types.mli

@@ -80,6 +80,8 @@ val release_order_full : api_release list
 
 val release_order : api_release list
 
+val latest_release : api_release
+
 exception Unknown_release of string
 
 exception UnspecifiedRelease

ocaml/idl/dm_api.ml

@@ -369,6 +369,7 @@ let check api emergency_calls =
   let are_in_vsn_order ps =
     let release_lt x y = release_leq x y && x <> y in
     let in_since releases =
+      let last = code_name_of_release latest_release in
       (* been in since the lowest of releases *)
       List.fold_left
         (fun sofar r ->
@@ -378,8 +379,7 @@ let check api emergency_calls =
           | r ->
               if release_lt r sofar then r else sofar
         )
-        (Xapi_stdext_std.Listext.List.last release_order |> code_name_of_release)
-        releases
+        last releases
     in
     let rec check_vsns max_release_sofar ps =
       match ps with

ocaml/libs/xapi-stdext/lib/xapi-stdext-std/listext.ml

@@ -75,13 +75,9 @@ module List = struct
     in
     loop 0 list
 
-  let rec last = function
-    | [] ->
-        invalid_arg "last: empty list"
-    | [x] ->
-        x
-    | _ :: xs ->
-        last xs
+  let head = function [] -> None | x :: _ -> Some x
+
+  let rec last = function [] -> None | [x] -> Some x | _ :: xs -> last xs
 
   let split_at n list =
     let rec loop i acc = function

ocaml/libs/xapi-stdext/lib/xapi-stdext-std/listext.mli

@@ -33,9 +33,11 @@ module List : sig
   element being the rest of elements of the list (or [] if the list is
   shorter). The results with negative values of [n] are the same as using 0. *)
 
-  val last : 'a list -> 'a
-  (** [last l] returns the last element of a list or raise Invalid_argument if 
-    the list is empty *)
+  val head : 'a list -> 'a option
+  (** [head l] returns the first element of [lst] or None if [lst] is empty *)
+
+  val last : 'a list -> 'a option
+  (** [last lst] returns the last element of [lst] or None if [lst] is empty *)
 
   val rev_mapi : (int -> 'a -> 'b) -> 'a list -> 'b list
   (** [rev_map f l] gives the same result as {!Stdlib.List.rev}[ (]

ocaml/libs/xapi-stdext/lib/xapi-stdext-std/listext_test.ml

@@ -14,7 +14,7 @@
 module Listext = Xapi_stdext_std.Listext.List
 
 let test_last_list tested_f (name, case, expected) =
-  let check () = Alcotest.(check @@ int) name expected (tested_f case) in
+  let check () = Alcotest.(check @@ option int) name expected (tested_f case) in
   (name, `Quick, check)
 
 let test_list tested_f (name, case, expected) =
@@ -31,10 +31,6 @@ let test_split_at_list tested_f (name, case, expected) =
   in
   (name, `Quick, check)
 
-let test_error tested_f (name, case, expected) =
-  let check () = Alcotest.check_raises name expected (tested_f case) in
-  (name, `Quick, check)
-
 let test_iteri_right =
   let specs =
     [
@@ -114,8 +110,7 @@ let test_drop =
   ("drop", tests)
 
 let test_last =
-  let specs = [([1], 0, 1); ([1; 2; 3], 1, 3)] in
-  let error_specs = [([], -1, Invalid_argument "last: empty list")] in
+  let specs = [([1], 0, Some 1); ([1; 2; 3], 1, Some 3); ([], -1, None)] in
   let test_good (whole, number, expected) =
     let name =
       Printf.sprintf "get last %i from [%s]" number
@@ -124,16 +119,7 @@ let test_last =
     test_last_list Listext.last (name, whole, expected)
   in
   let tests = List.map test_good specs in
-  let error_test (whole, number, error) =
-    let name =
-      Printf.sprintf "last [%s] with %i fails"
-        (String.concat "; " (List.map string_of_int whole))
-        number
-    in
-    test_error (fun ls () -> ignore (Listext.last ls)) (name, whole, error)
-  in
-  let error_tests = List.map error_test error_specs in
-  ("last", tests @ error_tests)
+  ("last", tests)
 
 let test_split_at =
   let specs =