A refused dyn view of a global names its own defining form as the fix, and every dyn fix is spelled in the syntax the code was written in

lib/check.ml

@@ -3454,7 +3454,13 @@ let view_elem_lit loc (k : int64) =
 (* A fix is spelled in the syntax of the file the mistake is in: the checker
    sees one AST for both, so the location's file is the only thing left that
    says which one the reader is looking at. *)
-let fln_source (loc : Loc.t) = Filename.check_suffix loc.Loc.file ".fln"
+let fln_source (loc : Loc.t) = Source.indented_at loc
+
+(* Which form defined each mutable global, [defonce] or [def], so a fix that
+   rewrites the definition keeps the form the programmer chose. Filled where
+   globals are collected; a name missing from it (a defconst) is given
+   [defonce]. *)
+let global_forms : (string, Ast.reinit) Hashtbl.t = Hashtbl.create 16
 
 (* The function being checked and its parameters, by slot. A stack because
    a generic's copy is checked from inside the body that called it. *)
@@ -3496,6 +3502,18 @@ let view_refusal kind loc (e : Tast.expr) reason =
       ( Printf.sprintf "%s is a %s parameter" n ty,
         Printf.sprintf "Declare %s as dyn in %s's parameters: %s%s" n f n
           (if fln then ": dyn" else " dyn") )
+    | None, Some n when (match e.Tast.e with Tast.Global _ -> true | _ -> false) ->
+      let every =
+        match e.Tast.e with
+        | Tast.Global g -> Hashtbl.find_opt global_forms g = Some Ast.Every
+        | _ -> false
+      in
+      ( Printf.sprintf "%s is a %s" n ty,
+        Printf.sprintf "Define %s as a dyn value, as in %s" n
+          (if fln then
+             Printf.sprintf "%s %s: dyn = [...]" (if every then "def" else "once") n
+           else
+             Printf.sprintf "(%s %s dyn [...])" (if every then "def" else "defonce") n) )
     | None, Some n ->
       ( Printf.sprintf "%s is a %s" n ty,
         Printf.sprintf "Build %s as a dyn value where it is made, as in %s" n
@@ -14601,6 +14619,7 @@ let collect env (decls : Ast.decl list) =
                (match k with Ast.Once -> "defonce" | Ast.Every -> "def") n
          in
          Hashtbl.replace env.globals n (ty, false);
+         Hashtbl.replace global_forms n k;
          Hashtbl.replace env.global_locs n loc
        | Ast.Defconst (n, Some t, _) ->
          Hashtbl.replace env.globals n (resolve env t, true);

test/test_syntax.ml

@@ -610,6 +610,28 @@ let () =
   checks "view-param-fix.fln"
     "fn take(d) -> i32 = 1\n\nfn give(n: i32, v: dyn) -> i32\n  take(v)\n\n\
      fn main() -> i32 = 0\n";
+  (* A global's fix redefines it, in the form it was defined with. *)
+  let show_flan = "(defn show [d dyn] i32 1)\n" in
+  refused "view-global.flan"
+    ("(defonce gs [2 i32] [1 2])\n" ^ show_flan ^ "(defn main [] i32 (show gs))\n")
+    [ "gs is a [2 i32]"; "as in (defonce gs dyn [...])" ];
+  refused "view-global-def.flan"
+    ("(def gs [2 i32] [1 2])\n" ^ show_flan ^ "(defn main [] i32 (show gs))\n")
+    [ "as in (def gs dyn [...])" ];
+  refused "view-global.fln"
+    "once gs: [2 i32] = [1 2]\n\nfn show(d) -> i32 = 1\n\nfn main() -> i32 = show(gs)\n"
+    [ "gs is a [2 i32]"; "as in once gs: dyn = [...]" ];
+  checks "view-global-fix.flan"
+    ("(defonce gs dyn [1 2])\n(def hs dyn [1 2])\n" ^ show_flan
+     ^ "(defn main [] i32 (show gs) (show hs))\n");
+  checks "view-global-fix.fln"
+    "once gs: dyn = [1 2]\n\nfn show(d) -> i32 = 1\n\nfn main() -> i32 = show(gs)\n";
+  (* The fix is spelled in the syntax the code was sent in, not the one the
+     file's name implies: an editor request from an indented buffer. *)
+  Source.with_code ~syntax:Source.Indented ~at:None (fun () ->
+    refused "unit-tail-request.flan"
+      "(defn f [coll] dyn (let [i 1] (while (< i 3) (++ i))))\n(defn main [] () (f 1))\n"
+      [ "fn f(...) -> ()" ]);
   (* The fix both of them name. *)
   checks "view-fix.fln"
     (poke_fln ^ "fn main() -> ()\n  let d: dyn = [6 2 4 9]\n  poke(d)\n  poke(the(dyn, [1 2]))\n");