Don't require/recommend ownership of /usr/local.

[MikeMcQuaid]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
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• Have you successfully run brew tests with your changes locally?

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Apple reset this on every OS X major (and some minor) updates and it always proves a painful and unnecessary step. Instead just check the directories we actually care about are writable.

This may mean if these directories do not already exist (although they are now created by the installed) that brew link will fail and require manual intervention but this seems to be superior for both new and the majority of existing users.

[DomT4]

Are we suggesting anything for the Caskroom, which lives in HOMEBREW_PREFIX by default now IIRC? Is there any situation where opt wouldn't be writable & that might need fixing?

Other than those two questions, seems reasonable 👍.

[MikeMcQuaid]

@DomT4 Caskroom is in HOMEBREW_REPOSITORY actually (which feels a little weird but is nice to avoid another root directory). Good call about opt, will check.

[zmwangx]

👍 on the change. Not directly related to this PR, but what about adding a warning on what chown -R actually does? Something like

Note that chown -R changes the ownership of all files and subdirectories, which could be slow and lead to unintended side effects if you have files and subdirectories that are not managed by Homebrew.

The reason is that chown -R could be very slow and doesn't print anything, so the user could decide that it's stuck and abort halfway, screwing up everything (unless running chown -R for a second time and letting it finish). Also, if there are software not managed by Homebrew installed to /usr/local, some could stop working correctly if you change the owner.

[MikeMcQuaid]

@zmwangx In my experience the longer you make these type of messages the less likely they are to be read. As we don't run them for users and they are recommendations I'm 🆒 with just trusting users .

[zmwangx]

In my experience the longer you make these type of messages the less likely they are to be read.

True 😓

[ilovezfs]

@MikeMcQuaid looks like this broke CI.

https://bot.brew.sh/job/Homebrew%20Core%20Pull%20Requests/7460/version=yosemite/console

for everything ...

[MikeMcQuaid]

Fix in #899.