bug#61668: Bug in flymake-proc with fix

[Camden Narzt via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Hi João,

Yeah I don’t use flymake-proc directly, I think lsp-mode is using it or something. Anyway I’ve attached a patch.

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--- flymake-proc.el.old	2023-02-21 09:12:10
+++ flymake-proc.el.new	2023-02-21 09:11:43
@@ -904,7 +904,7 @@
 (defun flymake-proc--delete-temp-directory (dir-name)
   "Attempt to delete temp dir DIR-NAME, do not fail on error."
   (let* ((temp-dir    temporary-file-directory)
-         (suffix      (substring dir-name (1+ (length (directory-file-name temp-dir))))))
+         (suffix      (substring dir-name (1+ (length (file-truename (expand-file-name (directory-file-name temp-dir))))))))
 
     (while (> (length suffix) 0)
       (setq suffix (directory-file-name suffix))

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Cheers,

Camden


> On Feb 21, 2023, at 5:42 AM, João Távora <joaotavora@gmail.com> wrote:
> 
> Hi Camden,
> 
> Flymake-proc is a deprecated part of Flymake.  I haven't used or tested
> it in a long time (there were never automated tests for it).  When I
> redesigned Flymake years ago, in which flymake-proc became another
> backend, I tested some basic use cases, but I didn't change the
> underlying code, including the directory calculating parts and helpers.
> 
> In other words, this is not "my code" and I never understood it.
> 
> So if you think the change makes sense, go for it i.e. provide a patch
> that we can push. I think there are very few users of this backend
> anyway.
> 
> João
> 
> On Tue, Feb 21, 2023 at 12:35 PM Eli Zaretskii <eliz@gnu.org> wrote:
>> 
>> Adding João.
>> 
>>> Date: Mon, 20 Feb 2023 11:23:02 -0700
>>> From:  Camden Narzt via "Bug reports for GNU Emacs,
>>> the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>>> 
>>> I’m sorry if this is not the correct place to report a flymake-proc bug, but since flymake is included in the emacs git repo I figured it might be ok.
>>> 
>>> I’m currently seeing incorrect behaviour from the `flymake-proc--delete-temp-directory` function. The path is parsed and then reassembled incorrectly as the following backtrace extract demonstrates:
>>> 
>>> flymake-proc--safe-delete-directory("/private/var/folders/p7/03_g5t611499lmjqhwc5tljr0000gn/T/000gn/T/Users/camdennarzt/Developer/Java/getargv.java/src/main/java/cam/narzt/getargv")
>>> flymake-proc--delete-temp-directory("/private/var/folders/p7/03_g5t611499lmjqhwc5tljr0000gn/T/Users/camdennarzt/Developer/Java/getargv.java/src/main/java/cam/narzt/getargv/“)
>>> 
>>> As you can see the `000gn/T/` segment of the path gets duplicated when `flymake-proc--safe-delete-directory` gets called.
>>> 
>>> This is because in `flymake-proc--delete-temp-directory` when the `suffix` variable is declared it is assumed that `(directory-file-name temporary-file-directory)` is a prefix of the `dir-name` argument, however `(directory-file-name temporary-file-directory)` doesn’t seem to resolve symlinks in the path whereas `dir-name` seems to have symlinks already resolved, so they don’t necessarily match. On my system the difference is:
>>> 
>>> (directory-file-name temporary-file-directory) → "/var/folders/p7/03_g5t611499lmjqhwc5tljr0000gn/T”
>>> dir-name → "/private/var/folders/p7/03_g5t611499lmjqhwc5tljr0000gn/T/Users/camdennarzt/Developer/Java/getargv.java/src/main/java/cam/narzt/getargv/“
>>> 
>>> Note the "/private” prefix on the `dir-name` path. That difference in length causes the suffix to be incorrectly determined and then causes a bunch of errors while any subsequent function call tries to work with a path with the `000gn/T/` segment duplicated which obviously doesn’t exist in the fs.
>>> 
>>> Changing the suffix variable to be computed as follows fixes the bug:
>>> 
>>> (substring dir-name (1+ (length (file-truename (expand-file-name (directory-file-name temp-dir))))))
>>> 
>>> 
>>> If this can be fixed that’s great, if there’s somewhere else I should report this I’d love to know.
>>> 
>>> Cheers,
>>> 
>>> Camden Narzt
>>> 
>>> 
>>> 
> 
> 
> 
> -- 
> João Távora