bug#61668: Bug in flymake-proc with fix

[Eli Zaretskii]

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
> 
> 
>