brew: keep HOMEBREW_PREFIX/bin in PATH with HOMEBREW_ENV_FILTERING

[maxim-belkin]

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Fixes #2875.

Basically, with HOMEBREW_ENV_FILTERING enabled, Homebrew filters out everything, including its own bin directory from PATH. This PR brings peace of mind to those who do HOMEBREW_ENV_FILTERING stuff occasionally.

$ export HOMEBREW_ENV_FILTERING=1
$ brew install subversion --with-python
$ ls -1 /usr/local/Cellar/subversion/1.9.7/lib/perl5/site_perl/
5.26.0
$ unset HOMEBREW_ENV_FILTERING
$ brew reinstall subversion
$ ls -1 /usr/local/Cellar/subversion/1.9.7/lib/perl5/site_perl/
5.26.0

[MikeMcQuaid]

Sorry but this ends up defeating much of the point of HOMEBREW_ENV_FILTERING by randomly adding things to the PATH based on user configuration (i.e. their chosen packages). 😭

[maxim-belkin]

Are you suggesting #2875 is not an issue and should be, in fact, closed?

[MikeMcQuaid]

I think it's an issue but the solution is using HOMEBREW_PATH inside relevant requirements.

[maxim-belkin]

How can Homebrew even think about Homebrew-ed perl if user does not specify anything on the command line?

[maxim-belkin]

Just a reminder, in #2875 the "problem" is that

brew install subversion --with-python

uses System's perl, not Homebrew-ed one.

There is nothing on the command line that would suggest that using system's Perl is wrong

[MikeMcQuaid]

I'm not sure I understand the question. Requirements can read the user's path with HOMEBREW_PATH and which through that to find what they want us to use but we don't want to expose that globally to e.g. the build process.

[maxim-belkin]

Em... Could you please elaborate on:

Requirements can read the user's path with HOMEBREW_PATH and which through that to find what they want us to use

Can't we assume that those who use Homebrew have HOMEBREW_PREFIX/bin in their PATH?

[maxim-belkin]

In subversion formula,

depends_on :perl => ["5.6", :recommended]

is satisfied by system's Perl even if Homebrew-ed Perl is installed and is better/newer.

So... because we do not tell Homebrew to use its own Perl and PATH is set in such a way that only system's Perl can be found, how can Homebrew even think about using Homebrew-ed Perl?

[MikeMcQuaid]

Can't we assume that those who use Homebrew have HOMEBREW_PREFIX/bin in their PATH?

Yes. Please check out the implementation of HOMEBREW_ENV_FILTERING. We reset the PATH and keep around HOMEBREW_PATH with the original user's value. The prior is used by the build process, the latter can be used by which in Requirements to add the full Cellar path to the PATH.

[maxim-belkin]

def which and def which_all in requirement.rb already consults ORIGINAL_PATHS.

[MikeMcQuaid]

Yes, which is why an additional fix would be required here...