Fix #2897 - Add extra_files option to flask run CLI

[rochacbruno]

Fix #2897

To define a list of files the reloader should watch additionally to the modules
as in extra_files argument used in the app.run and werkzeug.serving.run_simple
you can either use the --extra-files (or multiple -f) option or define the
FLASK_RUN_EXTRA_FILES environment variable.

    # on windows use ``;`` instead of ``:`` to separate paths
    export FLASK_RUN_EXTRA_FILES=/path/to/file1:/path/to/file2
    flask run
     * Running on http://127.0.0.1:8000/
     * Detected change in '/path/to/file1', reloading

On command line the same can be achieved with flask run -f /path/to/file1 -f /path/to/file2.

[rochacbruno]

The travis error

Traceback (most recent call last):
  File "/home/travis/build/pallets/flask/.tox/docs-html/lib/python3.6/site-packages/sphinx/config.py", line 161, in __init__
    execfile_(filename, config)
  File "/home/travis/build/pallets/flask/.tox/docs-html/lib/python3.6/site-packages/sphinx/util/pycompat.py", line 150, in execfile_
    exec_(code, _globals)
  File "conf.py", line 7, in <module>
    from pallets_sphinx_themes import DocVersion, ProjectLink, get_version
ImportError: cannot import name 'DocVersion'

ERROR: InvocationError for command '/home/travis/build/pallets/flask/.tox/docs-html/bin/sphinx-build -W -b html -d /home/travis/build/pallets/flask/.tox/docs-html/tmp/doctrees docs /home/travis/build/pallets/flask/.tox/docs-html/tmp/html' (exited with code 2)

Is also happening locally, all other envs of the tox matrix is passing except the docs. looks like recent changes to DocVersion location on pallets_sphinx_themes @davidism

[onovy]

please rebase on master, DocVersion import is already fixed

[rochacbruno]

@onovy done!

[davidism]

Current failures are due to Werkzeug master, don't worry about it.

[rochacbruno]

Do you still want this to be merged? should I rebase or close it?

[davidism]

currently working on Werkzeug

[davidism]

--extra-files implies that one option takes multiple values, when it really becomes --extra-files file1 --extra-files file2. Does --extra-file make sense instead? What about making a type that matches the behavior of the env var, so it really is just a single option separate by :? Also, except for -h and -p, no options have a short form.

[davidism]

Pushed a new version that adds a SeparatedPathType that allows --extra-files to be a single option that behaves like the env var. Removed the -f short option. Moved the docs to the section about development mode, since that's where the reloader is most relevant, although it might be good to reorganize / break up the CLI docs eventually.