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bug#36830: 26.2; find-file-visit-truename is not honored as file local v


From: Gustavo Barros
Subject: bug#36830: 26.2; find-file-visit-truename is not honored as file local variable
Date: Fri, 23 Aug 2019 18:38:40 -0300
User-agent: mu4e 1.2.0; emacs 26.2

Hi Eli, Hi Lars,

On Fri, Aug 23 2019, Eli Zaretskii wrote:

From: Lars Ingebrigtsen <address@hidden>
Date: Fri, 23 Aug 2019 20:59:55 +0200
Cc: address@hidden

      (if find-file-visit-truename
(setq buffer-file-name (expand-file-name buffer-file-truename)))

[...]

        (after-find-file error (not nowarn)))

`after-find-file' is the function that interprets the file local
variables, so we're setting the buffer file name before we've set that
variable locally.

One option would be to re-check the variable after `after-find-file',
but that seems a bit hacky.

Any opinions?

I don't think this variable was designed to be set from file-local
variables block.  Visiting a file and naming its buffer are two racy
actions, and where there's a race there will be chicken-and-egg type
of problems.

--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2413,7 +2413,11 @@ find-file-noselect-1
            (setq buffer-file-coding-system 'no-conversion)
            (set-buffer-major-mode buf)
            (setq-local find-file-literally t))
-       (after-find-file error (not nowarn)))
+       (after-find-file error (not nowarn))
+        ;; In case `find-file-visit-truename' is set as a file-local
+        ;; variable, recompute the buffer file name.
+        (when find-file-visit-truename
+ (setq buffer-file-name (expand-file-name buffer-file-truename))))

I expect such renaming to cause future bugs, FWIW.  Or maybe not, but
this is beyond hacky, IMO.

Maybe we should just document that this variable cannot be file-local.

I admittedly reported this from a user perspective, and do not fully grasp what is going on in this case. But I think I can add something here if I point that `vc-follow-symlinks` does work as a file local variable. Maybe I’m wrong in comparing these two variables, but if not, this could both provide some approach that works for this purpose, and could perhaps reduce the concerns raised by Eli.

I may also add that I would hardly set `find-file-visit-truename` globally, but I would find it useful locally (I don’t claim to be any reference in this respect though). Furthermore, if the race mentioned by Eli does prove to be insurmountable, and if there is any difference between setting this as "file-local" or as "dir-local", the latter could prove useful even if the former could not be maintained. (I don’t know if dir-local variables are set before the file is actually visited, but that is what I have in mind in mentioning this. If that is the case, the race might be thus circumvented.)

Best,
Gustavo.





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