flan/test/test_session.ml

(* The session: the declarations a running process was built from, plus every
   change accepted since (NEXT.md, the dev loop).

   Two halves. First, what a session refuses — every case here is a change that
   would compile, load, install, and then be wrong, because a cell is a bare
   pointer and storage that already exists already has a shape. Second, that
   refusing leaves the session usable, which is the failure people actually hit:
   one typo must not poison every later evaluation. *)

open Flan

let failures = ref 0
let fail fmt = Printf.ksprintf (fun s -> incr failures; print_endline ("FAIL  " ^ s)) fmt

let has hay needle =
  let n = String.length needle and h = String.length hay in
  let rec go i = i + n <= h && (String.sub hay i n = needle || go (i + 1)) in
  go 0

(* Every rejection is asserted on its reason, not just on the failure: the
   reason is the part that has to survive a refactor. *)
let refuses ?(file = "programs/reload.flan") name src reason =
  let t, _ = Session.create ~file in
  match Session.eval t src with
  | _ -> fail "%s was accepted" name
  | exception Loc.Error (_, msg) ->
    if not (has msg reason) then
      fail "%s\n        said: %S\n     wanted it to mention: %S" name msg reason

let () =
  (* A cell carries no signature, so every call site compiled before the change
     still passes the old arguments through it. *)
  (* [outer] is called only from C, and [spare] is read by nothing, so the
     checker has no complaint about either change and the session is the only
     thing that can refuse them. A change something else in the program uses is
     an ordinary type error first, which is a different and louder failure. *)
  refuses "a changed parameter type"
    "(defn outer [x i64] i64 (bump))"
    "changes signature";
  refuses "a changed return type"
    "(defn outer [] i32 (i32 (bump)))"
    "changes signature";
  refuses "a changed arity"
    "(defn outer [a i64 b i64] i64 (bump))"
    "changes signature";
  (* The storage exists and has a shape: reusing it reads at the wrong offsets,
     and replacing it discards the state the reload exists to preserve. *)
  refuses "a retyped global"
    "(defvar spare i32)"
    "changes type";
  (* Values of the type are already in the running program's memory. *)
  (* A defconst is folded into its call sites — into an array length, at worst,
     which is decided before any type resolves — so its value lives in the
     program's code and not only in its storage. *)
  refuses "a changed defconst"
    "(defconst folded i64 8)"
    "changes value";
  (* An enum member is erased to an i32 literal in the caller, so the same
     applies. It is compared over declarations because Tast.program carries no
     enums at all, for exactly that reason. *)
  refuses "a changed enum member"
    "(defenum Colour [red 0 green 2])"
    "changes its members";
  refuses ~file:"programs/values.flan" "a restructured struct"
    "(defstruct P [x i32 y i32])"
    "changes layout";

  (* An ordinary redefinition, and what the session works out about it. *)
  let t, _ = Session.create ~file:"programs/reload.flan" in
  let c = Session.eval t "(defn bump [] i64 (set counter (+ counter 5)) counter)" in
  if not c.Session.installs then fail "a redefined function had nothing to install";
  if c.Session.fns <> [ "bump" ] then
    fail "redefining bump reported %s" (String.concat " " c.Session.fns);
  (* The prelude is in the checked program and in no accumulated AST, so a
     session that derived [known] from declarations would call print-line
     through a registry cell nobody ever publishes. *)
  if not (has c.Session.ir "@\"flan.cell.print-line\" = external global ptr") then
    fail "the prelude was treated as new";
  if has c.Session.ir "flan_dev_cell" then
    fail "a name the host has went through the registry";

  (* A form that does not check must leave the session exactly as it was. This
     is the one that decides whether a REPL survives a typo. *)
  (match Session.eval t "(defn bump [] i64 nonsense)" with
   | _ -> fail "an unresolvable name was accepted"
   | exception Loc.Error _ -> ());
  (match Session.eval t "(defn bump [] i64 (set counter (+ counter 6)) counter)" with
   | c -> if c.Session.fns <> [ "bump" ] then fail "the session did not recover"
   | exception Loc.Error (_, m) -> fail "the session was poisoned by a typo: %s" m);

  (* A declaration the program already has, with no body and no new storage,
     is accepted and has nothing to send. Building a module for it would report
     success for a change that cannot have taken effect, and would cost the
     program a reload it did not need. *)
  (match Session.eval t "(defvar counter i64)" with
   | c -> if c.Session.installs then fail "an empty change claimed to install"
   | exception Loc.Error (_, m) -> fail "redeclaring a var unchanged: %s" m);

  (* A new global carries its declared initial value, copied once when the
     storage is allocated and never again — calloc alone would make it zero. *)
  let c = Session.eval t "(defvar started i64 42) (defn read-started [] i64 started)" in
  if not (has c.Session.ir "@\".init.") then
    fail "a new global's initialiser was dropped";
  if not c.Session.installs then fail "adding a global had nothing to install";

  (* Names the process was never built with go through the registry instead of
     binding to a symbol, and adding one is allowed where retyping one is not. *)
  let c = Session.eval t "(defvar fresh i64) (defn use-fresh [] i64 (set fresh 3) fresh)" in
  if not (List.mem "fresh" c.Session.names && List.mem "use-fresh" c.Session.fns) then
    fail "adding a var and a function reported %s" (String.concat " " c.Session.names);
  if not (has c.Session.ir "call ptr @flan_dev_global") then
    fail "a new global did not go through the registry";
  (* And once added, it is part of the session: a later form can use it. *)
  (match Session.eval t "(defn use-fresh [] i64 (set fresh 4) fresh)" with
   | _ -> ()
   | exception Loc.Error (_, m) -> fail "a name added earlier was forgotten: %s" m);

  (* A file with imports, re-evaluated whole — the C-c C-k case. The session
      keeps the *expanded* declarations, so the package's names are replaced in
      place rather than appended a second time and rejected as duplicates. *)
  let t, _ = Session.create ~file:"../sand.flan" in
  let src = In_channel.with_open_bin "../sand.flan" In_channel.input_all in
  (match Session.eval t src with
   | c ->
     if not (List.mem "game-draw" c.Session.fns) then
       fail "reloading sand.flan did not include its own functions"
   | exception Loc.Error (_, m) ->
     fail "reloading a file with imports failed: %s" m);

  (* A form typed into a file that is *imported as a package* has to be
     qualified the way the import qualified it, or it splices as a brand-new
     unrelated name: the evaluation reports success and the running program
     goes on calling the one it already had. The alias is chosen by the
     importer and written nowhere in the file, so the path is the only thing
     that can decide it — which is why it is derived here and not sent by the
     editor. *)
  let t, _ = Session.create ~file:"../sand.flan" in
  (match
     Session.eval ~origin:"../sand-sim/sim.flan" t
       "(defn settle [row i32 col i32] Unit (do))"
   with
   | c ->
     if c.Session.fns <> [ "sim/settle" ] then
       fail "a form from a package file reported %s, wanted sim/settle"
         (String.concat " " c.Session.fns)
   | exception Loc.Error (_, m) -> fail "redefining sim/settle: %s" m);
  (* And a file that is not a package keeps its names as written. *)
  (match Session.eval ~origin:"../sand.flan" t "(defn game-draw [] Unit (do))" with
   | c ->
     if c.Session.fns <> [ "game-draw" ] then
       fail "a form from the program's own file reported %s"
         (String.concat " " c.Session.fns)
   | exception Loc.Error (_, m) -> fail "redefining game-draw: %s" m);

  if !failures = 0 then print_endline "session: all tests passed"
  else begin
    Printf.printf "\n%d failure(s)\n" !failures;
    exit 1
  end