array elements are global (#67)

testsuite/tests/typing-local/local.ml

@@ -2573,3 +2573,39 @@ Line 3, characters 23-24:
                            ^
 Error: This value escapes its region
 |}]
+
+
+(* test of arrays *)
+(* as elements of arrays are mutable *)
+(* it is only safe for them to be at global mode *)
+(* cf: similarly reference cell can contain only global values *)
+
+(* on construction of array, we ensure elements are global *)
+
+let f (local_ x : string) = 
+  [|x; "foo"|]
+[%%expect{|
+Line 2, characters 4-5:
+2 |   [|x; "foo"|]
+        ^
+Error: This value escapes its region
+|}]
+
+let f (x : string) = 
+  [|x; "foo"|]
+[%%expect{|
+val f : string -> string array = <fun>
+|}]  
+
+
+(* on pattern matching of array, 
+   elements are strengthened to global 
+  even if array itself is local *)
+let f (local_ a : string array) = 
+  match a with
+  | [| x; _ |] -> ref x
+  | _ -> ref "foo"
+
+[%%expect{|
+val f : local_ string array -> string ref = <fun>
+|}]  

testsuite/tests/typing-local/nosyntax.ml

@@ -28,7 +28,10 @@ let local_ref (f : lfn -> unit) =
   f (fun s -> let _ = [|s;s;s|] in 1)
 
 [%%expect{|
-val local_ref : (lfn -> unit) -> unit = <fun>
+Line 2, characters 24-25:
+2 |   f (fun s -> let _ = [|s;s;s|] in 1)
+                            ^
+Error: This value escapes its region
 |}]
 
 type foo = {

typing/typecore.ml

@@ -2250,7 +2250,8 @@ and type_pat_aux
       end
   | Ppat_array spl ->
       let ty_elt = solve_Ppat_array ~refine loc env expected_ty in
-      map_fold_cont (fun p -> type_pat Value p ty_elt) spl (fun pl ->
+      map_fold_cont (fun p -> type_pat ~alloc_mode:(simple_pat_mode Value_mode.global)
+       Value p ty_elt) spl (fun pl ->
         rvp k {
         pat_desc = Tpat_array pl;
         pat_loc = loc; pat_extra=[];
@@ -4152,7 +4153,7 @@ and type_expect_
       let to_unify = Predef.type_array ty in
       with_explanation (fun () ->
         unify_exp_types loc env to_unify (generic_instance ty_expected));
-      let argument_mode = mode_subcomponent expected_mode in
+      let argument_mode = mode_global in
       let argl =
         List.map
           (fun sarg -> type_expect env argument_mode sarg (mk_expected ty))