`invenio webpack clean buildall` fails with `Module not found: Error: Can't resolve '@templates'`

[ZedThree]

Package version (if known): 1.3.0

Describe the bug

Running invenio webpack clean buildall fails because the templates directory is missing from the instance path

Steps to Reproduce

1. cookiecutter gh:inveniosoftware/cookiecutter-invenio-instance -c v3.4 --no-input
2. Install the following set of packages:

    invenio[auth, metadata, files, postgresql, elasticsearch7 ] >= 3.5.0a4
    invenio-admin >= 1.3.2,<1.4.0
    invenio-assets >= 1.3.0,<1.4.0
    invenio-formatter >= 1.1.3,<1.2.0
    invenio-logging >= 1.3.0,<1.4.0
    invenio-mail >= 1.0.2,<1.1.0
    invenio-rest >= 1.2.8,<1.3.0
    invenio-theme >= 1.3.17,<1.4.0
    lxml >=4.3.0,<5.0.0
    marshmallow >=3.0.0,<4.0.0
    uwsgi >=2.0
    uwsgi-tools >=1.1.1
    uwsgitop >=0.11

(Note that these are slightly different from those in the default Pipfile, notably invenio >= 3.5.0a4 and invenio-assets >= 1.3.0. We need to specify a whole bunch of other invenio-* packages because specifying invenio-assets manually clashes with invenio[base])
3. Run invenio webpack clean buildall
4. Get the following error:

ERROR in ./js/invenio_theme/templates.js
Module not found: Error: Can't resolve '@templates' in '/venv/var/instance/assets/js/invenio_theme'
 @ ./js/invenio_theme/templates.js 26:19-28:47
 @ ./js/invenio_search_ui/util.js
 @ ./js/invenio_search_ui/app.js

I managed to manually fix this by running mkdir /venv/var/instance/assets/templates, but it was pointed out in the Discord that invenio-cli symlinks this directory (although I couldn't work out what the target should be). However, if you're using Invenio Framework, then that tool won't work.

Could the webpack command itself instead take care of ensuring the directory exists?

[ZedThree]

I eventually found #134 and the discussion there led me to this comment in invenio-theme: https://github.com/inveniosoftware/invenio-theme/blob/28ae95cfebc8e96d6bb44afaf663c2bf9132c8dd/invenio_theme/webpack.py#L85-L90

The cause of my problem was that I'd moved the existing files out of theme/assets/semantic-ui/templates and deleted that directory. Restoring that directory and everything works as expected.

This was a really painful bug to track down because the error message appears to be completely unrelated to the actual problem. Is there some way these directories could be checked and a warning issued if the expected directory doesn't exist?