Brew: Add a check for branches of tapped repos

[JasonQSY]

I think it is a good idea to add at least a check for the branches of tapped repos. Generally, we are always using the master branch. However, if it is incorrectly switched to another branch like patch, it is better that brew update or brew doctor could have a warning.

The situation is that if we switch to another branch patch in usr/local/Homebrew/Library/Taps/homebrew/homebrew-core, brew update works correctly because it just pull the remote master branch to the local one. However, the active branch is patch and there is no warning in both brew update and brew doctor. And if other formulas work correctly requires a later version of formulas in homebrew-core, the installation fails.

It is not a big problem but tough to find the first time... That's why I think adding a check in brew update or at least brew doctor is a good idea. I could work on it if such a PR is welcomed.

[alyssais]

Having a doctor warning sounds good to me. 👍

[MikeMcQuaid]

@JasonQSY Could you try and open a pull request? This document should help and we're happy to walk you through anything else.

Thanks!

[JasonQSY]

OK. I'll try to work on it.

[MikeMcQuaid]

Fixed in https://github.com/Homebrew/brew/pull/3229