;;; test-flan-dev.el --- Drive the client against a running program  -*- lexical-binding: t; -*-

;; Run as:  emacs -Q --batch -L emacs -l emacs/test-flan-dev.el -- <socket> <flan-file>
;;
;; This is the client half of test_dev.ml.  The OCaml test proves the daemon
;; answers correctly; this proves the elisp actually talks to it — the framing,
;; the reply reader, and C-c C-c picking the right form out of a buffer.  A
;; protocol bug that only shows up under Emacs' coding systems would pass the
;; OCaml test and fail here, which is the whole reason it exists.

;;; Code:

(require 'flan-mode)
(require 'flan-dev)
(require 'flan-repl)

(defvar test-flan--failures 0)

(defmacro test-flan--said (&rest body)
  "Run BODY and return the last thing it put in the echo area.
`current-message' is nil under --batch, so the echo area is watched where it
is written instead — the real `message' call the real command makes."
  `(let* ((said nil)
          (probe (lambda (fmt &rest args)
                   (when fmt (setq said (apply #'format fmt args))))))
     (advice-add 'message :before probe)
     (unwind-protect (progn ,@body)
       (advice-remove 'message probe))
     said))

(defun test-flan--check (name ok)
  (if ok (message "  ok   %s" name)
    (setq test-flan--failures (1+ test-flan--failures))
    (message "  FAIL %s" name)))

(let* ((args (cdr (member "--" command-line-args)))
       (socket (nth 0 args))
       (file   (nth 1 args))
       (flan   (nth 2 args))
       ;; The buffer above is a copy in a temporary directory; this is the
       ;; program where it actually lives, which is the one a second daemon
       ;; can be started on — an `import' is resolved from the importing
       ;; file's own directory, and a copy in /tmp has no packages above it.
       (program (nth 3 args)))
  (find-file file)
  ;; The copy comes out of a build directory, so it may arrive read-only.
  ;; Set the flag directly: `read-only-mode' asks about the file on disk, and
  ;; a question in a batch run is a hang waiting to happen.
  (setq buffer-read-only nil)
  (test-flan--check "flan-mode is on for a .flan file" (eq major-mode 'flan-mode))

  (test-flan--check "the modeline says so before connecting"
                    (and (eq (flan-dev-state) 'off)
                         (string-match-p "off" (flan-dev-mode-line))))

  (flan-connect socket)
  (test-flan--check "connected" (process-live-p flan-dev--connection))
  (test-flan--check "the modeline says a program is there"
                    (and (eq (flan-dev-state) 'live)
                         (string-match-p "live" (flan-dev-mode-line))))
  (test-flan--check "and says nothing in a buffer that is not Flan's"
                    (with-temp-buffer (null (flan-dev-mode-line))))
  ;; Buffer-locally, so that someone who loads this and never opens a .flan
  ;; file is not evaluating it on every redisplay of every buffer they have.
  (test-flan--check "the indicator is in this buffer's modeline"
                    (member '(:eval (flan-dev-mode-line)) mode-line-misc-info))
  (test-flan--check "and not in everyone else's"
                    (with-temp-buffer
                      (not (member '(:eval (flan-dev-mode-line))
                                   mode-line-misc-info))))

  ;; A daemon restarted while Emacs was not looking is the ordinary case.  The
  ;; socket outlives this connection, so dropping the process and asking again
  ;; is the same situation the client meets after a restart, and it must come
  ;; back rather than fail.
  (delete-process flan-dev--connection)
  (test-flan--check "a dead connection reads as lost, not as never-connected"
                    (and (eq (flan-dev-state) 'lost)
                         (string-match-p "lost" (flan-dev-mode-line))))
  (let ((r (flan-dev--request '(:op "describe"))))
    (test-flan--check "the next request reconnects on its own"
                      (and (process-live-p flan-dev--connection)
                           (member "step" (plist-get r :fns)))))
  ;; ...and knows the program's names again.  An empty cache after a reconnect
  ;; is honest but silent: eldoc goes quiet and M-. falls through to another
  ;; backend, with nothing said about why.
  (test-flan--check "and knows the program's names again"
                    (assoc "step" flan-dev--defs))

  ;; But a socket nobody is listening on is refused by name, rather than
  ;; retried forever or reported as some other failure.
  (let ((flan-dev--connection nil)
        (flan-dev--socket "/nonexistent/flan-dev-not-here.sock")
        (raised nil))
    (condition-case err (flan-dev--request '(:op "describe"))
      (error (setq raised (error-message-string err))))
    (test-flan--check "a socket that is gone is refused by name"
                      (and raised
                           (string-match-p "flan-dev-not-here.sock" raised)
                           (string-match-p "nothing is listening" raised))))

  (let ((r (flan-dev--request '(:op "describe"))))
    (test-flan--check "describe lists the program's functions"
                      (member "step" (plist-get r :fns)))
    (test-flan--check "describe lists the program's globals"
                      (member "ticks" (plist-get r :globals))))

  ;; C-c C-c on the form at point: put point inside `step' and send it.  The
  ;; text comes from the buffer, so this exercises `beginning-of-defun' against
  ;; Flan's own syntax table as much as it does the wire.
  (goto-char (point-min))
  (search-forward "(defn step")
  (goto-char (match-beginning 0))
  (save-excursion
    (search-forward "(+ ticks 1)")
    (replace-match "(+ ticks 41)"))
  (let ((form (flan-dev--defun-at-point)))
    (test-flan--check "the form at point is the defn"
                      (and (string-prefix-p "(defn step" (string-trim form))
                           (string-match-p "41" form))))
  (flan-eval-defun)

  ;; And an error: the daemon answers with a location, the client raises.
  (let ((raised nil))
    (condition-case err
        (flan-dev--eval "(defn step [] i64 nonsense)" "form")
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "a form that does not check is reported"
                      (and raised (string-match-p "unknown name" raised))))

  ;; The :loc column is a *byte* offset — lib/reader.ml walks the source a byte
  ;; at a time — and Emacs counts characters.  Same rule as the framing, a
  ;; different place to get it wrong, and it shows up only for someone whose
  ;; comments or identifiers are not ASCII.
  (with-temp-buffer
    (insert ";; héllo\n(defn wörld [] i64 nonsense)\n")
    (let ((want (save-excursion
                  (goto-char (point-min))
                  (search-forward "nonsense")
                  (match-beginning 0)))
          (eol (save-excursion (goto-char (point-min)) (line-end-position))))
      (test-flan--check "a byte column lands on the right character"
                        (= (flan-dev--position
                            2 (1+ (string-bytes "(defn wörld [] i64 ")))
                           want))
      (test-flan--check "a column past the end of a line is clamped to it"
                        (= (flan-dev--position 1 500) eol))))

  ;; A rejected form is marked where it is, not only in the echo area.  The
  ;; daemon numbers lines from the start of what it was sent, so a form taken
  ;; from the middle of a buffer only lands on the right line because the
  ;; client pads it back into place before sending.
  (goto-char (point-min))
  (search-forward "(defn step")
  (goto-char (match-beginning 0))
  (let ((defn-line (line-number-at-pos)))
    (save-excursion
      (search-forward "(+ ticks 41)")
      (replace-match "(+ ticks nonsense)"))
    (ignore-errors (flan-eval-defun))
    (let ((ovs (seq-filter (lambda (o) (overlay-get o 'flan-dev-error))
                           (overlays-in (point-min) (point-max)))))
      (test-flan--check "a rejected form gets exactly one error overlay"
                        (= 1 (length ovs)))
      (test-flan--check "the overlay is at the form, not at line 1"
                        (and ovs (>= (line-number-at-pos (overlay-start (car ovs)))
                                     defn-line)))
      (test-flan--check "the overlay carries the daemon's reason"
                        (and ovs
                             (string-match-p
                              "unknown name"
                              (or (overlay-get (car ovs) 'help-echo) ""))))
      (test-flan--check "and shows it beside the code"
                        (and ovs
                             (string-match-p
                              "unknown name"
                              (or (overlay-get (car ovs) 'after-string) "")))))
    ;; ...and it goes away when the next evaluation is accepted.  A marker left
    ;; behind after a fix is a lie about the running program.  Point moved to
    ;; the error, which is the point of all this, so start the search over.
    (goto-char (point-min))
    (search-forward "(+ ticks nonsense)")
    (replace-match "(+ ticks 41)")
    (search-backward "(defn step")
    ;; A silent success is indistinguishable from a silent failure, so an
    ;; accepted evaluation says what landed in the running program and what it
    ;; cost.  The name comes from the *reply*: the daemon is the one that knows
    ;; which names it installed.
    (let ((said (test-flan--said (flan-eval-defun))))
      (test-flan--check "an accepted evaluation clears it"
                        (null (seq-filter (lambda (o) (overlay-get o 'flan-dev-error))
                                          (overlays-in (point-min) (point-max)))))
      (test-flan--check "and says which name landed"
                        (and said (string-match-p "\\_<step\\_>" said)))
      (test-flan--check "and how long it took"
                        (and said (string-match-p "[0-9]+ ms" said)))))

  ;; A declaration the program already has installs nothing, and must say so
  ;; rather than reporting a time for a build that did not happen.
  (let ((said (test-flan--said
               (flan-dev--eval "(defvar ticks i64)" "form"))))
    (test-flan--check "an evaluation with nothing to install says so"
                      (and said (string-match-p "nothing to install" said)
                           (not (string-match-p "installed" said)))))

  ;; Many names are counted and sampled.  An echo area truncated in the middle
  ;; of the tenth name says neither how many there were nor which.
  (test-flan--check "a long list of names is counted, not cut off"
                    (equal (flan-dev--names-phrase
                            '("a" "b" "c" "d" "e" "f") "fallback")
                           "6 names (a, b, c, d, …)"))
  (test-flan--check "a short one is just named"
                    (equal (flan-dev--names-phrase '("a" "b") "fallback") "a, b"))

  ;; `defs' is what eldoc, completion and M-. all read.  One op answering all
  ;; three, cached, because eldoc fires on an idle timer and completion inside
  ;; redisplay, and neither may block on a socket.
  (test-flan--check "the program's names are known"
                    (assoc "step" flan-dev--defs))
  (test-flan--check "with a signature"
                    (equal (nth 2 (assoc "step" flan-dev--defs)) "step [] i64"))
  (test-flan--check "a global is known, and says it is one"
                    (equal (nth 1 (assoc "ticks" flan-dev--defs)) "var"))
  (test-flan--check "so is an imported package's extern"
                    (let ((d (assoc "agent/wait-raw" flan-dev--defs)))
                      (and d (equal (nth 1 d) "extern"))))
  ;; `step' was last installed from this buffer, so that is where the daemon
  ;; says it is — which is also the check that the client's line padding put it
  ;; on the line it is really on rather than on line 1.
  (test-flan--check "a fn carries where it is written"
                    (equal (nth 3 (assoc "step" flan-dev--defs))
                           (format "%s:%d:7" buffer-file-name
                                   (save-excursion
                                     (goto-char (point-min))
                                     (search-forward "(defn step")
                                     (line-number-at-pos)))))

  ;; eldoc: the signature of the name at point, and of the form point is
  ;; inside, which is what you want while typing arguments.
  (goto-char (point-min))
  (search-forward "(set ticks (step")
  (let ((said nil))
    (test-flan--check "eldoc answers for the name at point"
                      (and (flan-dev-eldoc-function
                            (lambda (s &rest _) (setq said s)))
                           said (string-match-p "step \\[\\] i64" said))))
  (let ((said nil))
    (save-excursion
      (goto-char (point-min))
      (search-forward "(set ticks (step)")
      (backward-char 1)            ; inside (step ...), not on the name
      (flan-dev-eldoc-function (lambda (s &rest _) (setq said s))))
    (test-flan--check "and for the form point is inside"
                      (and said (string-match-p "step" said))))
  (let ((said nil))
    (with-temp-buffer
      (insert "not-a-flan-name")
      (flan-dev-eldoc-function (lambda (s &rest _) (setq said s))))
    (test-flan--check "and says nothing about a name the program has not got"
                      (null said)))

  ;; Completion: the running program's names, through `completion-at-point'.
  (goto-char (point-min))
  (search-forward "(defn step")
  (let* ((capf (flan-dev-completion-at-point))
         (table (nth 2 capf)))
    (test-flan--check "completion offers the program's own names"
                      (member "step" (all-completions "ste" table)))
    (test-flan--check "and the names an import brought in"
                      (member "agent/wait" (all-completions "agent/" table)))
    (test-flan--check "and annotates each with what it is"
                      (equal (funcall (plist-get (nthcdr 3 capf)
                                                 :annotation-function)
                                      "ticks")
                             "  var")))

  ;; M-. through xref, so it is the key it always is.
  (let ((xs (xref-backend-definitions 'flan "step"))
        (line (save-excursion (goto-char (point-min))
                              (search-forward "(defn step")
                              (line-number-at-pos))))
    (test-flan--check "M-. finds where a function is written"
                      (and (= 1 (length xs))
                           (let ((l (xref-item-location (car xs))))
                             (and (file-equal-p (xref-location-group l)
                                                buffer-file-name)
                                  (= (xref-location-line l) line))))))

  ;; And the two things it cannot do, refused by name with the reason rather
  ;; than by opening an empty buffer.
  (let ((raised nil))
    (condition-case err (xref-backend-definitions 'flan "ticks")
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "M-. on a global refuses, saying why"
                      (and raised (string-match-p "ticks" raised)
                           (string-match-p "no location" raised))))
  (let ((raised nil))
    (condition-case err (xref-backend-definitions 'flan "print-line")
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "M-. into the prelude refuses, saying why"
                      (and raised (string-match-p "prelude" raised)
                           (string-match-p "not a file on disk" raised))))
  (let ((raised nil))
    (condition-case err (xref-backend-definitions 'flan "no-such-name")
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "and so does a name the program does not have"
                      (and raised (string-match-p "no no-such-name" raised))))

  ;; A name installed now must complete now, not after the next connect.
  (flan-dev--eval "(defn freshly-added [] i64 7)" "form")
  (test-flan--check "a name just installed is known immediately"
                    (equal (nth 2 (assoc "freshly-added" flan-dev--defs))
                           "freshly-added [] i64"))

  ;; The session is not poisoned by that: a good form still lands.
  (flan-dev--eval "(defn step [] i64 (set ticks (+ ticks 100)) ticks)" "form")

  ;; The program's own output arrives on replies and lands in its buffer, so
  ;; a long-running program is not writing into a terminal nobody is watching.
  (flan-dev--eval "(defn step [] i64 (do (print-line \"HELLO\") ticks))" "form")
  (let ((seen nil) (deadline (+ (float-time) 10)))
    (while (and (not seen) (< (float-time) deadline))
      (ignore-errors (flan-dev--request '(:op "describe")))
      (setq seen (with-current-buffer (get-buffer-create flan-dev-output-buffer)
                   (string-match-p "HELLO" (buffer-string)))))
    (test-flan--check "the program's output reaches its buffer" seen))

  ;; The REPL buffer: typed input goes through the same eval-expr request, and
  ;; the value lands at the prompt while the program's own output goes to
  ;; *flan-output*. Conflating those two is the bug worth testing for.
  (test-flan--check "an incomplete form is not sent"
                    (not (flan-repl--complete-p "(+ 1")))
  (test-flan--check "a whole form is sent" (flan-repl--complete-p "(+ 1 2)"))
  (test-flan--check "a paren in a string does not count"
                    (not (flan-repl--complete-p "(f \"(\"")))
  (flan-repl)
  (with-current-buffer flan-repl-buffer
    (goto-char (point-max))
    (insert "(+ 20 3)")
    (flan-repl-return)
    (let ((deadline (+ (float-time) 15)))
      (while (and (not (string-match-p "23" (buffer-string)))
                  (< (float-time) deadline))
        (accept-process-output nil 0.05)))
    (test-flan--check "the REPL shows a value"
                      (string-match-p "23" (buffer-string)))
    (goto-char (point-max))
    (insert "no-such-thing")
    (flan-repl-return)
    (let ((deadline (+ (float-time) 15)))
      (while (and (not (string-match-p "unknown name" (buffer-string)))
                  (< (float-time) deadline))
        (accept-process-output nil 0.05)))
    (test-flan--check "the REPL shows an error"
                      (string-match-p "unknown name" (buffer-string)))
    ;; A value and the program's output travel by different routes: the value
    ;; is the result of the request, the output rides along with the reply.
    ;; Showing them in one place would be convenient and wrong.
    (goto-char (point-max))
    (insert "(print-line \"PRINTED\")")
    (flan-repl-return)
    (let ((deadline (+ (float-time) 15)))
      (while (and (not (with-current-buffer flan-dev-output-buffer
                         (string-match-p "PRINTED" (buffer-string))))
                  (< (float-time) deadline))
        (ignore-errors (flan-dev--request '(:op "describe")))
        (accept-process-output nil 0.05)))
    (test-flan--check "printed text goes to the output buffer"
                      (with-current-buffer flan-dev-output-buffer
                        (string-match-p "PRINTED" (buffer-string))))
    ;; ...and the prompt got the *value*, which for a call made for its effect
    ;; is Unit. The text it printed is not the value and does not belong here.
    (test-flan--check "and the prompt got the value, not the text"
                      (string-match-p "()" (buffer-string))))

  ;; ── The break loop ────────────────────────────────────────────────────
  ;;
  ;; An unhandled `error' stops the program on the frame that erred instead of
  ;; killing it, and this is the half of that an editor sees: it has to notice
  ;; without being told, say what stopped it, offer the restarts, and keep
  ;; working while the program sits there.  Last in this file because the
  ;; program is left running afterwards but its `step' has been through a
  ;; break, and nothing above should have to reason about that.

  ;; Refused while it is running, by name.  There is no restart stack to walk
  ;; from a running program, and an empty prompt would be worse than a refusal.
  (let ((raised nil))
    (condition-case err (flan-break)
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "the prompt refuses while the program is running"
                      (and raised (string-match-p "running" raised))))

  ;; The poll is a real timer, registered on connect.  What it *does* is
  ;; checked below by calling it; that it is scheduled at all is checked here,
  ;; because a background discovery that nothing ever runs discovers nothing.
  (test-flan--check "a poll timer is running"
                    (and (timerp flan-dev--timer)
                         (eq (timer--function flan-dev--timer) #'flan-dev--poll)))

  ;; Break it: `step' is called every time round the program's loop, so a body
  ;; that errors stops it on its own game thread, in a frame of its own — not
  ;; inside anything this client asked for.  Nothing tells Emacs.
  (flan-dev--eval
   "(defn step [] i64 (restart-case (do (error (Missing {:id 7})) 0) (use-placeholder [] -1)))"
   "form")
  (let ((deadline (+ (float-time) 20)))
    (while (and (not flan-dev--stopped) (< (float-time) deadline))
      (flan-dev--poll)
      (accept-process-output nil 0.05)))
  (test-flan--check "the client notices a stop nobody asked about"
                    (equal flan-dev--stopped "Missing"))
  (test-flan--check "and the modeline says so, with the condition"
                    (and (eq (flan-dev-state) 'stopped)
                         (string-match-p "stopped" (flan-dev-mode-line))
                         (string-match-p "Missing" (flan-dev-mode-line))))

  ;; What the prompt would offer.  `completing-read' is not driven here — a
  ;; minibuffer in a batch run is a hang waiting to happen — so the list it
  ;; reads and the two commands it dispatches to are exercised instead.
  (test-flan--check "the restarts on offer are the ones the frame declared"
                    (equal (flan-dev-restarts) '("use-placeholder")))

  ;; And what it would put in front of someone.  The labels carry the position,
  ;; because the position is what gets chosen: two frames may offer the same
  ;; name and only a number can say which one.  A pure function over a reply,
  ;; so it is checked against the shapes a real daemon cannot easily be made to
  ;; produce as well as against the one it just did.
  (test-flan--check "the prompt numbers what it offers"
                    (equal (flan-dev--restart-candidates '("use-placeholder") nil)
                           '(("0. use-placeholder" . 0))))
  (test-flan--check "a shadowed name is two distinguishable choices"
                    (equal (mapcar #'cdr
                                   (flan-dev--restart-candidates
                                    '("retry" "use-placeholder" "retry") nil))
                           '(0 1 2)))
  (test-flan--check "a restart below the break is shown, and shown as such"
                    (let ((table (flan-dev--restart-candidates
                                  '("retry" "use-placeholder") '(1))))
                      (and (not (string-match-p "cannot be taken" (caar table)))
                           (string-match-p "cannot be taken" (car (nth 1 table)))
                           (equal (cdr (nth 1 table)) 1))))

  ;; The payoff.  The break loop *is* the poll loop, so an expression sent now
  ;; runs on the stopped thread and comes back — which is the one moment
  ;; anybody actually wants C-x C-e to work.
  (goto-char (point-max))
  (let ((beg (point)))
    (insert "\n(+ 20 3)")
    (let ((said (test-flan--said (flan-eval-last-sexp))))
      (test-flan--check "C-x C-e works while the program is stopped"
                        (and said (string-match-p "23" said))))
    (delete-region beg (point-max)))

  ;; And installing, which the break loop allows on purpose: there is no frame
  ;; in progress, so the rule against swapping a body that is on the stack does
  ;; not apply.  This is the fix-it-and-retry loop — the broken `step' is
  ;; replaced here, and the resume below returns into the old one for the last
  ;; time before every later call reaches the new body through its cell.
  (let ((said (test-flan--said
               (flan-dev--eval "(defn step [] i64 (set ticks (+ ticks 1)) ticks)"
                               "form"))))
    (test-flan--check "a fix installs while the program is stopped"
                      (and said (string-match-p "\\_<step\\_>" said))))

  ;; Choosing one.  "ok" from the daemon means accepted — the stopped thread
  ;; takes it on its next pass — so the client stops claiming a break and lets
  ;; the next poll settle it.
  ;; By position, which is the path `C-c C-b' takes: the name goes with it as
  ;; the receipt the program checks, not as the lookup.
  (flan-dev-restart-at 0 "use-placeholder")
  (let ((deadline (+ (float-time) 20)))
    (while (and (not (eq (flan-dev-state) 'live)) (< (float-time) deadline))
      (flan-dev--poll)
      (accept-process-output nil 0.05)))
  (test-flan--check "choosing a restart resumes the program"
                    (and (null flan-dev--stopped)
                         (eq (flan-dev-state) 'live)))

  ;; ...and the client is an ordinary client again on the far side of it.
  (goto-char (point-max))
  (let ((beg (point)))
    (insert "\n(+ 1 1)")
    (let ((said (test-flan--said (flan-eval-last-sexp))))
      (test-flan--check "and everything works again afterwards"
                        (and said (string-match-p "2" said))))
    (delete-region beg (point-max)))

  ;; ── The documentation buffer ──────────────────────────────────────────
  ;;
  ;; The same four facts `defs' carries, in a buffer: eldoc answers while you
  ;; are typing, and a signature in the echo area is gone the moment you do
  ;; anything else.  Run before the disconnect below, because it reads the
  ;; running program.
  (flan-doc "step")
  (with-current-buffer flan-doc-buffer
    (let ((text (buffer-string)))
      (test-flan--check "the doc buffer names the thing and its signature"
                        (and (string-match-p "\\`step" text)
                             (string-match-p "step \\[\\] i64" text)))
      (test-flan--check "and says what kind of thing it is"
                        (string-match-p "Kind +fn" text))
      ))
  ;; Where it is written, for a name that has not been re-installed from a
  ;; buffer since the daemon built it: `main' is still at the location the
  ;; daemon read it from, which is the ordinary case and the one with a
  ;; button on it.
  (flan-doc "main")
  (with-current-buffer flan-doc-buffer
    (test-flan--check "and where a definition is written"
                      (string-match-p
                       (regexp-quote (file-name-nondirectory program))
                       (buffer-string))))
  ;; A global has no Loc in the Tast, so the buffer says that in the same words
  ;; M-. refuses in — rather than leaving the line out, which reads as though
  ;; the name had no home at all.
  (flan-doc "ticks")
  (with-current-buffer flan-doc-buffer
    (test-flan--check "a global says why there is no location"
                      (string-match-p "no location for a var" (buffer-string))))
  (let ((raised nil))
    (condition-case err (flan-doc "no-such-name")
      (user-error (setq raised (error-message-string err))))
    (test-flan--check "and a name the program has not got is refused"
                      (and raised (string-match-p "no no-such-name" raised))))

  (flan-disconnect)
  (test-flan--check "disconnected" (not (process-live-p flan-dev--connection)))
  (test-flan--check "and the poll timer is cancelled with it"
                    (null flan-dev--timer))

  ;; ── Starting the daemon from Emacs ────────────────────────────────────
  ;;
  ;; Last, and after the disconnect above, because it runs a *second* daemon:
  ;; nothing before this should have to reason about which of two programs a
  ;; request went to.  Its own socket for the same reason — and because
  ;; `flan dev' with no -s puts one beside the program, which for a test
  ;; program in /tmp is a path shared with every other thing running there.
  (setq flan-dev-command flan)
  (let ((socket2 (concat socket "-started-from-emacs")))
    (ignore-errors (delete-file socket2))
    (test-flan--check "nothing to quit before anything was started"
                      (let ((raised nil))
                        (condition-case err (flan-dev-quit)
                          (user-error (setq raised (error-message-string err))))
                        (and raised (string-match-p "no daemon started" raised))))
    (flan-dev program socket2)
    (test-flan--check "M-x flan-dev builds, launches and connects"
                      (and (process-live-p flan-dev--daemon)
                           (eq (flan-dev-state) 'live)))
    (test-flan--check "and it is the program that was asked for"
                      (member "step" (plist-get (flan-dev--request '(:op "describe"))
                                                :fns)))
    ;; Refused rather than silently restarted: a second daemon would take the
    ;; first one's program and everything in its memory with it.
    (test-flan--check "a second one is refused while the first is alive"
                      (let ((raised nil))
                        (condition-case err (flan-dev program socket2)
                          (user-error (setq raised (error-message-string err))))
                        (and raised (string-match-p "already running" raised))))
    ;; The daemon owns the program's lifetime, so quitting has to actually end
    ;; the process — not just drop the socket and leave it running.
    ;; Restarting the program: for a change the running one cannot take — a
    ;; struct whose layout moved — where the answer is a new build, a new
    ;; process and the session that compiled it.  Proved by what it throws
    ;; away: a name installed into the old program is not in the new one.
    (flan-dev--eval "(defn only-in-the-old-program [] i64 1)" "form")
    (test-flan--check "a name installed into the running program is there"
                      (assoc "only-in-the-old-program" flan-dev--defs))
    (let ((old flan-dev--daemon))
      (flan-dev-restart-program)
      (test-flan--check "restarting gives a different daemon, connected"
                        (and (not (process-live-p old))
                             (process-live-p flan-dev--daemon)
                             (not (eq old flan-dev--daemon))
                             (eq (flan-dev-state) 'live))))
    (test-flan--check "and a program built from source, without the addition"
                      (and (assoc "step" flan-dev--defs)
                           (null (assoc "only-in-the-old-program"
                                        flan-dev--defs))))

    (let ((proc flan-dev--daemon))
      (flan-dev-quit)
      ;; The process, not the variable: forgetting a daemon is not stopping
      ;; one, and a program left running with nothing attached to it is
      ;; exactly what the terminal loop used to leave behind.
      (test-flan--check "quitting ends the daemon"
                        (and (not (process-live-p proc))
                             (null flan-dev--daemon)
                             (not (process-live-p flan-dev--connection))
                             (eq (flan-dev-state) 'off)))
      ;; The daemon unlinks its socket on the way out, so this is the same
      ;; claim seen from the other side.
      (test-flan--check "and takes its socket with it"
                        (not (file-exists-p socket2))))
    (ignore-errors (delete-file socket2)))

  ;; A program that does not exist is refused here rather than by a daemon
  ;; that starts, fails to build and exits — which looks the same from a
  ;; distance and takes a compile to find out.
  (test-flan--check "a file that is not there is refused before anything starts"
                    (let ((raised nil))
                      (condition-case err (flan-dev "/nonexistent/nope.flan")
                        (user-error (setq raised (error-message-string err))))
                      (and raised (string-match-p "no such file" raised))))

  ;; ── Navigating a file ─────────────────────────────────────────────────
  ;;
  ;; No daemon in any of this: imenu and which-function read the buffer, which
  ;; is the point — they work on a file nobody has run yet, and they keep
  ;; working when the program is stopped or gone.
  (with-temp-buffer
    (insert ";;;; A file with one of everything.\n"
            "(defstruct Missing [id i32])\n"
            "(defvar ticks i64)\n"
            "(defconst limit i64 10)\n"
            "(declare later [] i64)\n"
            "(defn step [] i64\n"
            "  (let [x 1]\n"
            "    (defn not-top-level [] i64 2)\n"
            "    (+ ticks x)))\n")
    (flan-mode)
    (let* ((index (imenu--make-index-alist))
           (group (lambda (name) (cdr (assoc name index)))))
      (test-flan--check "imenu finds a function, where it is written"
                        (equal (marker-position
                                (cdr (assoc "step" (funcall group "Functions"))))
                               (save-excursion (goto-char (point-min))
                                               (search-forward "(defn step")
                                               (match-beginning 0))))
      (test-flan--check "and a struct, under its own heading"
                        (assoc "Missing" (funcall group "Types")))
      (test-flan--check "and both kinds of global"
                        (and (assoc "ticks" (funcall group "Variables"))
                             (assoc "limit" (funcall group "Variables"))))
      ;; A forward declaration is not a definition; listing it beside one
      ;; would show the same name twice with nothing to tell them apart.
      (test-flan--check "and a declaration, said to be one"
                        (and (assoc "later" (funcall group "Declared"))
                             (null (assoc "later" (funcall group "Functions")))))
      ;; A `defn' inside a `let' defines nothing at the top level, and the
      ;; index is anchored at column 0 so that it cannot offer one.
      (test-flan--check "and nothing that is not a top-level form"
                        (null (assoc "not-top-level" (funcall group "Functions")))))
    ;; which-function: the case is a long body scrolled past its own header.
    (goto-char (point-min))
    (search-forward "(+ ticks x)")
    (test-flan--check "which-function names the definition point is in"
                      (equal (flan-current-defun-name) "step"))
    (goto-char (point-min))
    (test-flan--check "and says nothing above the first one"
                      (null (flan-current-defun-name))))

  ;; ── A rejection lasts as long as the action it was about ──────────────
  ;;
  ;; The overlay is feedback on the evaluation that just failed, so the next
  ;; command in that buffer takes it down.  What is checked here is the
  ;; mechanism and not Emacs' command loop: `execute-kbd-macro' under --batch
  ;; runs no `pre-command-hook' at all (and does not even move point), so there
  ;; is no way from here to make the real loop run one.  `run-hooks' is what
  ;; the loop calls, and calling it is the closest honest thing — it proves the
  ;; hook is installed, in the right buffer and nowhere else, and that running
  ;; it clears the overlay and uninstalls itself.  It does not prove Emacs runs
  ;; it, which is Emacs' own contract.
  (let ((buf (flan-dev--buffer-visiting file)))
    (with-current-buffer buf
      (flan-dev-clear-errors)
      (let ((marked (flan-dev--show-error (format "%s:2:1" file) "no such name")))
        (test-flan--check "a rejection is marked in the buffer it came from"
                          (and marked (flan-dev--error-overlays)))
        (test-flan--check "and the buffer is armed to take it down again"
                          (memq #'flan-dev--clear-errors-on-command
                                pre-command-hook))
        ;; Buffer-local, or every buffer in the session runs this on every
        ;; keystroke for the sake of a buffer that had one bad evaluation.
        (test-flan--check "and nobody else is"
                          (not (memq #'flan-dev--clear-errors-on-command
                                     (default-value 'pre-command-hook))))
        (run-hooks 'pre-command-hook)
        (test-flan--check "the next command in that buffer clears it"
                          (null (flan-dev--error-overlays)))
        (test-flan--check "and the hook goes with the last overlay"
                          (not (memq #'flan-dev--clear-errors-on-command
                                     pre-command-hook))))))

  ;; ── Disassembly ───────────────────────────────────────────────────────
  ;;
  ;; Its own daemon, because the first one was disconnected above and a
  ;; disassembly is a question only a live session can answer: the daemon is
  ;; the thing that built the module and still has the .ll and the .so.
  (let ((socket3 (concat socket "-disasm")))
    (ignore-errors (delete-file socket3))
    (flan-dev program socket3)
    (test-flan--check "a daemon to disassemble against"
                      (process-live-p flan-dev--connection))

    (when (executable-find "objdump")
      (flan-disassemble "step")
      (with-current-buffer flan-disassembly-buffer
        (let ((text (buffer-string)))
          (test-flan--check "C-c C-a writes a disassembly of the name"
                            (string-match-p "\\`; disassembly for step" text))
          ;; The header is the half a listing cannot carry: what the answer
          ;; claims, which for generated code is never "this is running".
          (test-flan--check "with the daemon's own account of what it shows"
                            (string-match-p "showing" text))
          (test-flan--check "and instructions under it, numbered from zero"
                            (string-match-p "^  0000  " text)))))

    ;; The other half of the same question, on the same body.
    (flan-disassemble "step" t)
    (with-current-buffer flan-disassembly-buffer
      (let ((text (buffer-string)))
        (test-flan--check "C-u C-c C-a writes the IR it was built from"
                          (and (string-match-p "\\`; LLVM IR for step" text)
                               (string-match-p "^define .*flan\\.step" text)))
        ;; Nothing has been evaluated into this daemon, so the body in the
        ;; cell is still the one the process was launched with — the one case
        ;; where what is installed *now* is knowable, and it says so.
        (test-flan--check "and says the program is still running the host's copy"
                          (string-match-p "host executable" text))))

    ;; Refused by name rather than shown as an empty buffer.
    (test-flan--check "a name the program does not define is refused by name"
                      (let ((raised nil))
                        (condition-case err (flan-disassemble "no-such-thing")
                          (user-error (setq raised (error-message-string err))))
                        (and raised (string-match-p "no function named" raised))))
    (test-flan--check "and so is a global, which has no code to show"
                      (let ((raised nil))
                        (condition-case err (flan-disassemble "ticks")
                          (user-error (setq raised (error-message-string err))))
                        (and raised (string-match-p "not a function" raised))))

    (flan-dev-quit)
    (ignore-errors (delete-file socket3)))

  (if (zerop test-flan--failures)
      (message "flan-dev.el: all tests passed")
    (message "\n%d failure(s)" test-flan--failures)
    (kill-emacs 1)))

;;; test-flan-dev.el ends here