Blacklist known bad Erlang releases, fixes #1857

[wohali]

Some of the changes to .travis.yml are temporary - once the test run looks correct, a screenshot of the output will be added and the known-bad versions will be removed.

In support of #1870
Closes #1857

[wohali]

So we have a problem. Travis only has 20.3.8, 20.3.8.1 and 20.3.8.5 available for testing. They don't actually have 20.3.8.11 or higher. (Inventory: https://s3.amazonaws.com/travis-otp-releases)

Options:

• Get Travis admins to provide 20.3.8.18.
• Detect that we're in a Travis CI run and skip the version check (see nNck's comment below)
• Force Travis to use kerl to build 20.3.8.11+, which would happen every build. (Big slowdown.)
• Install 20.3.8.18 from packages.erlang-solutions.com in .travis.yml. (Fiddly .travis.yml work.)
• Print a warning at compile time instead of a hard halt.
• Print a warning instead of a hard halt, but only when we match against 20.3.8
• Don't have Travis test against 20.3.8 anymore, just 19.3 and 21.2.3 (or newer)

@davisp @nickva @janl what do you think?

[nickva]

Maybe don't halt on 20.3.8 and print the warning if running in Travis? There is TRAVIS=true environment variable we can check I think. With some comment saying "when/if 20.3.8.11 + becomes available we'll make it halt".

[wohali]

I opted to wrap the halt call in a check for the TRAVIS envvar. We should be smart enough to not put a bad version number intentionally into .travis.yml.

./configure locally fails on 20.3.8.6, 20.3, and 21.2.
./configure locally passes on 19.3.6.8, 20.3.8.18 and 21.2.3.

[nickva]

I think can simplify the test with:

case VerList of
    [20 | _] = V20 when V20 < [20, 3, 8, 11] -> NotSupported(VerString);
    [20 | _] = V20 when V20 >=  [20, 3, 8, 11] -> ok;
    [21, 2] -> NotSupported(VerString);
    [21, 2, N | _] when N < 3 -> NotSupported(VerString);
    _ -> ok
end.

This would take care of 20.2.9.9 type versions. What we are saying there if it's a 20 version, anything less than 20.3.8.11 is no good. Otherwise (>=) it's ok.

[nickva]

+1