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.)