On Wed, 18 Sep 2019 at 16:45, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Juanma Barranquero <lekktu@gmail.com>
> > Date: Wed, 18 Sep 2019 17:01:19 +0200
> > Cc: martin rudalics <rudalics@gmx.at>, Eli Zaretskii <eliz@gnu.org>,
> >  Paul Eggert <eggert@cs.ucla.edu>, Emacs Development <
> emacs-devel@gnu.org>
> >
> > > "emacs -Q" starts OK. Doing [M-x load-library RET package RET] fails
> with "Opening stdio stream: No such
> > file or directory, package".
> >
> >  I've bootstrapped Emacs and I don't see that problem.
> >
> > emacs -Q
> > M-x load-library <RET> package <RET>
> >
> > works as expected.
>
> Richard said "installs", so maybe this problem only happens in an
> installed Emacs?  Richard, do you see the same problem if you run
> Emacs from its build tree?  To simulate an uninstalled Emacs, you
> might need to rename the versioned subdirectory under the share/emacs/
> directory where you install Emacs.
>

That could be the difference. I usually install Emacs, despite the
inconvenience, because then emacs.exe lives alongside all the DLLs it will
need and I can set $PATH and `exec-path' to any convenient value for
subprocesses.

Emacs does launch correctly (at least, it displays a frame) if I run it
from the src directory (I didn't need to move the versioned directory
aside).

I have rebuilt Emacs from a clean repo, and the problem still exists. (If I
launch the installed version I get the message I mentioned, and no frame is
displayed, and Emacs exits.)