Aside from being bad style, this also assigns to an unused variable.

If rubocop invocation from brew audit exits with nil exitstatus,
brew audit fails with 'undefined method `>' for nil:NilClass'.

Also prevent the commit of formula's HeadVersion from passing to the resource. 

This is a fix of #531

On systems prior to 10.9, formulae that use CVS as a download source
check whether the installed Xcode already provides CVS to avoid adding
a dependency on the `cvs` formula. Unfortunately, if no Xcode is
installed the check fails with

  undefined method `<' for nil:NilClass

causing the formula to become unloadable. This in turn causes some taps
to be untappable since #396 added the `readall` check on `tap`.

Closes #508.

Closes #529.

Signed-off-by: Xu Cheng <xucheng@me.com>

This prevents a link conflict during `brew upgrade` causing opt link
stuck to old version. At this point, users will have to run `brew switch`
to fix it.

Closes #533.

Signed-off-by: Xu Cheng <xucheng@me.com>

Switch to HOMEBREW_LIBRARY since HOMEBREW_LIBRARY_PATH already includes
"/Homebrew" and HOMEBREW_LIBRARY is less confusing.

Closes #530.

Signed-off-by: ilovezfs <ilovezfs@icloud.com>

Closes #478.

Signed-off-by: Xu Cheng <xucheng@me.com>

Substitue each Version.new and HeadVersion.new with Version.create
to unify Version and HeadVersion instantiation among core code.

Note that this does not relate to Mac::OS::Version class.

* Test `Formula#update_head_version`
* Test `Formula#latest_head_prefix`

We're moving more stuff to Homebrew Cask which is better maintained and run.

Closes https://github.com/Homebrew/brew/issues/519
Closes https://github.com/Homebrew/homebrew-core/issues/3029

Move some stuff formerly in `Library/ENV` around:
- Move `Library/ENV/$XCODE_VERSION` to `Library/Homebrew/env/super` as they are
  all superenv wrappers and all symlinks to the same version. We never needed
  the "separate shims for separate versions" functionality and it just adds
  confusion.
- Move `Library/ENV/pkgconfig` to `Library/Homebrew/env/pkgconfig` to get more
  things under `Library/Homebrew`
- Move `Library/ENV/scm` to `Library/scm` as these wrappers are not actually
  used by or related to superenv (or stdenv) in any way.

Users may have ~/.curlrc file to include options like proxies.
However, since we overwrite HOME environment variable during the build
and test, curl won't be able to find it.

This commit solves this issue by using CURL_HOME environment variable,
which will be pointed to the original HOME path.

From `curl(1)`:
> 1) curl tries to find the "home dir": It first  checks  for  the
     CURL_HOME and then the HOME environment variables. Failing that,
     it uses getpwuid() on Unix-like systems (which returns the  home
     dir  given the current user in your system). On Windows, it then
     checks for the APPDATA variable, or as a last resort the '%USER-
     PROFILE%\Application Data'.

Closes #514.

Signed-off-by: Xu Cheng <xucheng@me.com>

This makes `Tab` compatible with `BuildOptions`.

No longer needed in `super.rb` after it was moved to `os/mac`.

Looks like it was accidentally left behind (?)

In https://github.com/Homebrew/brew/commit/0d189fae57bad6c209b471eba9e0b254a2b40886
we completely removed `effective_sysroot`, which consequently left all the
`effective_sysroot`/usr/include calls pointing at `/usr/include`. This is wildly
problematic on systems where the Command Line Tools aren't installed because
`/usr/include` is not a default-created folder prior to CLT installation.

I'm unsure if `effective_sysroot` should still be mentioned in Library/Homebrew/extend/ENV/super.rb
at all. If it can be deleted, feel free to do that without waiting for me to review.

This seems to fix:
* https://github.com/Homebrew/homebrew-core/issues/2991
* https://github.com/Homebrew/homebrew-core/issues/2986
* https://github.com/Homebrew/homebrew-core/issues/2962

* test-bot: start running generic tests.

Start running the test suite in the "generic" mode i.e. a base layer for
non-OS X platforms to be able to use to ensure we don't break the generic code
for the parts of the code we've got running.

Currently this just runs the integration tests as that's the only useful suite
that's entirely passing but eventually this will be changed to run the full test
suite in generic mode.

* test_integration_cmds: fix tests on Linux.