Re: Testing redisplay code in batch

[Alan Mackenzie]

Hello, Stefan.

On Tue, Sep 22, 2020 at 23:56:33 -0400, Stefan Monnier wrote:
> I have a test for the Bug#43519 which I'd like to add to our test suite,
> but it requires the redisplay to do its job, and in batch mode it seems
> that Mr. Redisplay gets quite sloppy.

> Does someone have experience with batch-tests of redisplay code?

> So far I've only use the "let-bind execute-kbd-macro to t" trick in
> order to convince minibuffer functions to actually use a minibuffer
> and process events from `unread-command-events`, but here I need to go
> further because I the "dummy windows" used in batch mode aren't
> good enough.

> So I'm ideally looking for a way to convince Emacs's internals to
> perform redisplay as if there were "real" windows.  I don't need to
> "see/display" the result, OTOH because I only need to test things like
> `window-start` and `window-end` after calling `redisplay`.

> If that can't be done without major surgery to the C code, has someone
> already setup some way to run interactive tests in some virtual
> interactive session (I guess using something like a detached `screen` or
> `tmux`)?

Have a look at .../tests/000tests.el in standalone CC Mode.  In
particular, look at this function (which has been in place for ~18
years):

(defun cc-test-force-font-lock-buffer ()
  ;; Try to forcibly font lock the current buffer, even in batch mode.
  ;; We're doing really dirty things to trick font-lock into action in
  ;; batch mode in the different emacsen.
  (let ((orig-noninteractive-function
         (and (fboundp 'noninteractive)
              (symbol-function 'noninteractive)))
        (orig-noninteractive-variable
         (and (boundp 'noninteractive)
              (symbol-value 'noninteractive)))
        ;; font-lock in XEmacs 19 looks at a variable named `noninteractive'.
        (noninteractive nil))
    (unwind-protect
        (progn
          (when orig-noninteractive-function
            ;; XEmacs (at least 21.4) calls `noninteractive' to check
            ;; for batch mode, so we let it lie.
            (fset 'noninteractive (lambda () nil)))
          (font-lock-mode 1)
          (unless (or (get-text-property (point-min) 'face)
                      (next-single-property-change (point-min) 'face))
            ;; Some emacsen have already fontified the buffer above,
            ;; but others need some more coercion..
            (let (;; Avoid getting some lazy fontification package that
                  ;; might decide that nothing should be done.
                  (font-lock-fontify-buffer-function
                   'font-lock-default-fontify-buffer))
              (font-lock-fontify-buffer))))
      (when orig-noninteractive-function
        (fset 'noninteractive orig-noninteractive-function)))))

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).