feat: Enhance mutability checks

Signed-off-by: Kakadu <Kakadu@pm.me>

CHANGES

@@ -18,6 +18,7 @@
 - #15: Split 'string_concat' lint to check separately patterns 'a^b^c' (level=Allow) and 'List.fold_left (^)' (level=Warn).
   (reported by @edwintorok)
 - #16: Calculate test coverage.
+- The lint 'mutable_hashtables' now check for mutability in general: references, mutable record fields, etc.
 
 
 ## 1.0.0 (24-03-2023)

src/typed/Hashtables.ml

@@ -12,6 +12,8 @@ type input = Tast_iterator.iterator
 
 let lint_source = LINT.FPCourse
 let lint_id = "mutable_hashtables"
+
+(* TODO: rename that it checks mutability in general *)
 let level = LINT.Warn
 
 let documentation =
@@ -95,6 +97,21 @@ let run _ fallback =
         let loc = typ.Typedtree.ctyp_loc in
         check loc pat_typ typ;
         fallback.typ self typ)
+  ; type_declaration =
+      (fun self td ->
+        fallback.type_declaration self td;
+        match td.Typedtree.typ_type.Types.type_kind with
+        | Types.Type_abstract | Type_open -> ()
+        | Type_record (labels, _) ->
+          List.iter labels ~f:(function
+            | { ld_mutable = Mutable; ld_loc = loc; _ } ->
+              CollectedLints.add
+                ~loc
+                (report loc.Location.loc_start.Lexing.pos_fname ~loc ())
+            | _ -> ())
+        | Type_variant _ ->
+          (* TODO(Kakadu): Algbraic constuctors could have mutable record arguments *)
+          ())
   ; expr =
       (fun self expr ->
         let loc = expr.Typedtree.exp_loc in

tests/typed/hashtables.t/Hashtables.ml

@@ -17,3 +17,8 @@ let get_unique_identity_code () =
   let code = !last_identity in
   last_identity := code + 1;
   code
+
+module BindsMap = Map.Make(String)
+type env = int option ref BindsMap.t
+
+type args = { mutable count: int }

tests/typed/hashtables.t/run.t

@@ -24,3 +24,11 @@
   18 |   last_identity := code + 1;
          ^^^^^^^^^^^^^
   Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standart tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.
+  File "Hashtables.ml", line 22, characters 11-25:
+  22 | type env = int option ref BindsMap.t
+                  ^^^^^^^^^^^^^^
+  Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standart tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.
+  File "Hashtables.ml", line 24, characters 14-32:
+  24 | type args = { mutable count: int }
+                     ^^^^^^^^^^^^^^^^^^
+  Alert zanuda-linter: Using mutable data structures for teaching purposes is usually discouraged. Replace Hashtables by standart tree-like maps or consider Hash-Array Mapped Tries (HAMT). Use mutable `ref`erences and mutable structure fields only if it is really required. In all places where it is needed indeed, describe in a comment why it is needed there.