Deprecated brew tap-pin usage consistently fails CI if cache is not present

[mbdevpl]

Expected behaviour

After forking, I expected the CI to work in the fork.

Actual behaviour

Builds are consistently failing due to usage of deprecated (see https://brew.sh/2019/04/04/homebrew-2.1.0/ and Homebrew/brew#5925) brew tap-pin functionality.

The problem is in line 101 of travis_config.sh:

brew tap --list-pinned | grep -qxF cartr/qt4 || brew tap-pin cartr/qt4

In the main repo, the first part brew tap --list-pinned | grep -qxF cartr/qt4 always succeeds, I assume because the cache always kicks in.

In the fork however, it always falls through to brew tap-pin cartr/qt4 because there is no cache, and then it always fails, so cache is never created. If only I could escape this catch 22 ;)

Steps to reproduce

1. Fork the repo.
2. Enable Travis CI builds for the fork.
3. Trigger a build.
4. See it crash and burn.

Bunch of examples: https://travis-ci.com/mbdevpl/opencv-python/builds

One specific log: https://travis-ci.com/mbdevpl/opencv-python/jobs/263773575 - in this build no changes have been made in the fork whatsoever, it's simply a build of current master branch.

Solution idea

I guess one quick solution to try would be to use:

brew tap-pin cartr/qt4/formula_name_here

But unfortunately as I am unfamiliar with the opencv-python CI setup, I have no idea about what should be in the formula_name_here. Would any one of maintainers be able to provide ideas to try?

[mbdevpl]

And after I solve this in my fork, I'd like to submit a PR so that other new forks don't get stuck on this issue in the future.

[mbdevpl]

@skvark Thanks for merging! You might wanna trigger a new build so that cache is fully re-generated because of:

https://travis-ci.org/skvark/opencv-python/jobs/622109414

Building dependencies took too long. Restart the build in Travis UI to continue from cache.

[mbdevpl]

I had click there myself once as well to finish setting up the initial cache. I think somehow the pull request might have triggered a cache rebuild for the main repo...

[skvark]

Ah, yes. I cleared the Travis cache because if there's a long time between builds homebrew recipes fail to update sometimes which makes the cache build fail.