bug#63337: [PATCH] package-vc--build-documentation: Fix relative @include statements

[Eli Zaretskii]

> From: Joseph Turner <joseph@breatheoutbreathe.in>
> Cc: Eli Zaretskii <eliz@gnu.org>, 63337@debbugs.gnu.org
> Date: Mon, 08 May 2023 12:05:51 -0700
> 
> Note about the following two lines:
> 
> + (file-path (expand-file-name file (package-desc-dir pkg-desc)))
> + (default-directory (expand-file-name (file-name-directory file-path)))
> 
> (package-desc-dir pkg-desc) may return a relative path with or without a
> directory, e.g. "doc/manual.org" or "manual.org". In the latter case,
> (file-name-directory "manual.org") would return `nil' and
> (expand-file-name nil) would signal an error.
> 
> Therefore, in the `file-path' `let'-binding, we first expand the return
> value of (package-desc-dir pkg-desc) to ensure that it contains a directory.

Please don't use "path" for anything that is not a PATH-style list of
directory: the GNU Coding Standards frown on such usage.  We use
file-name instead.  For the same reasons, please don't give your
variables names that include "path" unless they are lists of
directories.

> --- a/lisp/emacs-lisp/package-vc.el
> +++ b/lisp/emacs-lisp/package-vc.el
> @@ -376,14 +376,17 @@ Package specs are loaded from trusted package archives."
>  FILE can be an Org file, indicated by its \".org\" extension,
>  otherwise it's assumed to be an Info file."
>    (let* ((pkg-name (package-desc-name pkg-desc))
> -         (default-directory (package-desc-dir pkg-desc))
> +         (file-path (expand-file-name file (package-desc-dir pkg-desc)))
> +         ;; `let'-bind `default-directory' to the directory containing the 
> .org or .info FILE
> +         ;; so that makeinfo can resolve relative @include statements in the 
> docs directory.
> +         (default-directory (expand-file-name (file-name-directory 
> file-path)))

There should be no reason to call expand-file-name in the last line,
since the argument of file-name-directory is already expanded.

Also, please make the comment lines shorter, preferably less than 75
columns.

Thanks.