Re: master c4d34d2: CC Mode: Enhance C++ Mode raw strings to multi-line strings for any language

[Alan Mackenzie <acm@muc.de>]

Hello, Basil.

On Thu, Aug 19, 2021 at 01:15:04 +0100, Basil L. Contovounesios wrote:

[ .... ]

> Tonight, I tried the following approach instead (in an unedited source
> tree):

> 0. C-x p c make TEST_LOAD_EL=no test/electric-tests RET
> 1. M-! pkill -SIGUSR2 -f ert-run-tests RET

> I repeated this a few times, and the *emacs-compilation* buffer reliably
> contained the same backtrace:

> --8<---------------cut here---------------start------------->8---
> Test electric-layout-plainer-c-mode-use-c-style backtrace:
>   c-tnt-chng-cleanup(nil [(nil . t) #<buffer *Test buffer (electric-la
>   #f(compiled-function () #<bytecode 0x1ce6cae08acf>)()
>   c-point-syntax()
>   electric-layout-for-c-style-du-jour(123)
>   electric-layout-post-self-insert-function-1()
>   electric-layout-post-self-insert-function()
>   self-insert-command(1 123)
>   funcall-interactively(self-insert-command 1 123)
>   call-interactively(self-insert-command)
>   #f(compiled-function () #<bytecode -0x8b013aec04deab5>)()
>   ert--call-with-test-buffer(nil #f(compiled-function () #<bytecode -0
>   #f(compiled-function () #<bytecode -0x10479e86da51cfc>)()
>   ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
>   ert-run-test(#s(ert-test :name electric-layout-plainer-c-mode-use-c-
>   ert-run-or-rerun-test(#s(ert--stats :selector ... :tests ... :test-m
>   ert-run-tests((not (or (tag :unstable) (tag :nativecomp))) #f(compil
>   ert-run-tests-batch((not (or (tag :unstable) (tag :nativecomp))))
>   ert-run-tests-batch-and-exit((not (or (tag :unstable) (tag :nativeco
>   eval((ert-run-tests-batch-and-exit '(not (or (tag :unstable) (tag :n
>   command-line-1(("-L" ":." "-L" "./../../elpa/packages/url-http-ntlm/
>   command-line()
>   normal-top-level()
> Test electric-layout-plainer-c-mode-use-c-style condition:
>     Buffer: *Test buffer (electric-layout-plainer-c-mode-use-c-style)*
>     (quit)
>      QUIT    5/478  electric-layout-plainer-c-mode-use-c-style (54.497779 sec)
> --8<---------------cut here---------------end--------------->8---

> Sprinkling some prints in c-tnt-chng-cleanup revealed that the following
> loop never terminates:

>   (let ((undo-in-progress t))
>     (while (not (eq (setq buffer-undo-list
>                           (primitive-undo 1 buffer-undo-list))
>                     saved-undo-list))))

> HTH,

That helps a great deal, thanks!

The problem is a bug in c-point-syntax.  There, there is
  (i) an invocation of c-save-buffer-state, which binds buffer-undo-list
  to t, followed by
  (ii) an invocation of c-tentative-buffer-changes, which pushes nil onto
  buffer-undo-list (simulating an undo group) giving (nil t).
  (iii) A { is typed into the buffer, giving buffer-undo-list now as
  something like ((5128 . 5129) nil t).
At this point garbage collection occurs.  This strips the tail of
buffer-undo-list, leaving ((5128 . 5129)).
  (iv) In c-tnt-chng-cleanup, primitive-undo is repeated infinitely,
  since buffer-undo-list will never become the expected value (nil t).

The problem would appear to be the invalid value ((5128 . 5129) nil t) in
buffer-undo-list.

I'll see what I can do about this tonight.

> -- 
> Basil

-- 
Alan Mackenzie (Nuremberg, Germany).