bug#45287: 28.0.50; byte-compile-file results in error with commit fe50a8b9ba or later on master

[Philipp Stephani <p.stephani2@gmail.com>]

Am Do., 17. Dez. 2020 um 09:23 Uhr schrieb Yasuhiro KIMURA <yasu@utahime.org>:
>
> commit fe50a8b9ba
> Author: Philipp Stephani <phst@google.com>
> Date:   Sun Dec 13 17:13:50 2020 +0100
>
>     Byte compilation: handle case where the output file is a mountpoint.
>
>     See Bug#44631.  While testing for a readonly output directory has
>     slightly different semantics, in practice they should cover cases
>     where Emacs is sandboxed and can only write to the destination file,
>     not its directory.
>
>     * lisp/emacs-lisp/bytecomp.el (byte-compile-file): Handle the case
>     where the output directory is not writable.
>
>     * test/lisp/emacs-lisp/bytecomp-tests.el
>     (bytecomp-tests--not-writable-directory)
>     (bytecomp-tests--dest-mountpoint): New unit tests.
>
> With this commit or later on master,
>
> https://github.com/yasuhirokimura/tamago/tree/fix_build_after_the_removal_of_make_coding_system
>
> build of this application fails as following.
>
> if test "emacs" != "no"; then \
>   am__dir=. am__subdir_includes=''; \
>   case cannarpc.elc in */*) \
>     am__dir=`echo 'cannarpc.elc' | sed 's,/[^/]*$,,'`; \
>     am__subdir_includes="-L $am__dir -L ./$am__dir"; \
>   esac; \
>   test -d "$am__dir" || /usr/bin/mkdir -p "$am__dir" || exit 1; \
>   emacs --batch \
>     -q -no-site-file -no-init-file --eval="(setq load-path (append (list (expand-file-name \"..\")) load-path))" --eval="(load \"docomp.el\")"  \
>     $am__subdir_includes -L . -L . \
>     --eval "(defun byte-compile-dest-file (f) \"cannarpc.elc\")" \
>     --eval "(unless (byte-compile-file \"cannarpc.el\") (kill-emacs 1))"; \
> else :; fi
> Loading c:/Users/yasu/Work/Emacs/master/tamago/docomp.el (source)...
> Package cl is deprecated
> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>   file-writable-p(nil)
>   byte-compile-file("cannarpc.el")
>   (if (byte-compile-file "cannarpc.el") nil (kill-emacs 1))
>   (unless (byte-compile-file "cannarpc.el") (kill-emacs 1))
>   eval((unless (byte-compile-file "cannarpc.el") (kill-emacs 1)) t)
>   command-line-1(("--eval=(setq load-path (append (list (expand-file-..." "--eval=(load \"docomp.el\")" "-L" "." "-L" "." "--eval" "(defun byte-compile-dest-file (f) \"cannarpc.elc\")" "--eval" "(unless (byte-compile-file \"cannarpc.el\") (kill-em..."))
>   command-line()
>   normal-top-level()

Thanks for the report, fixed with commit
7fad9591142f9d9d0bfce37dd8c65a847dbe8aa9.