[Avocado-devel] Implement fetch-assets command line

[Willian Rampazzo]

Hello everyone,

I started working on Trello card
https://trello.com/c/T3SC1sZs/1521-implement-fetch-assets-command-line
as part of a broader card,
https://trello.com/c/CKP7YS6G/1481-on-cache-check-for-asset-fetcher
and I would like to bring my findings to a discussion.

One way to implement that would be to parse the test source looking
for the fetch_asset call and execute it. In theory, it is a straight
forward implementation.

I have started working in the parser. After some simple tests, some
complex situations started to show up. Let me bring an existing
example, examples/tests/assets.py:

    def setUp(self):
        mirrors = ['https://mirrors.peers.community/mirrors/gnu/hello/',
                   'https://mirrors.kernel.org/gnu/hello/',
                   'http://gnu.c3sl.ufpr.br/ftp/',
                   'ftp://ftp.funet.fi/pub/gnu/prep/hello/']
        hello = 'hello-2.9.tar.gz'
        hello_locations = ["%s/%s" % (loc, hello) for loc in mirrors]
        hello_sig = 'hello-2.9.tar.gz.sig'
        hello_sig_locations = ["%s/%s" % (loc, hello_sig) for loc in mirrors]
        self.hello = self.fetch_asset(
            name=hello,
            locations=hello_locations)
        self.hello_sig = self.fetch_asset(
            name=hello_sig,
            asset_hash='f3b9fae20c35740004ae7b8de1301836dab4ac30',
            locations=hello_sig_locations)

When the parser finds the fetch_asset call, it needs to inspect its
arguments, looking for variables. If any variable is found, it needs
to walk back the code looking for its assignment, so it is able to
execute it prior to the fetch_asset execution. If the variables
consist of other variables, the parser, again, needs to walk back in
the code looking for those assignments, and so on.

There are countless ways of creating the right side of a variable
assignment, from a single string assignment to a function that builds
the content, or conditional assignments.

My initial idea is to cover variables consisting of other variables
and list comprehension, just like in the example. For now, other
complex constructions would be out of this implementation.

Any comment, concern, suggestion, is appreciated here as it would help
to build a more robust code.

Best regards,

Willian Rampazzo
Software Engineer
Red Hat Brazil
2717 337F 7E4A 5FDF