Use classes for instance doubles.

Rename `test/cask/cli` to `test/cask/cmd`.

Deprecate `brew cask --version`.

Remove redundant namespacing.

Add `$LOAD_PATH` for RuboCop cops.

rust/cargo: enable caching

README: add maintainers.

Add Steven to maintainers and Dom to PLC.

scm shim: handle edge case

Since #4748 `HOMEBREW_GIT` is set by the `brew.sh`, whose value is default to be `git`.
As a result, it completely bypasses the logic of the shims/scm/git.

This fixes the issue by checking whether `HOMEBREW_GIT` and
`HOMEBREW_SVN` are set to be `git` and `svn` respectively.

Fixes #4825.

Change regex to match `filename` if header also contains `filename*`.

utils: Use JSON to marshal child errors

Refactor `Hbc::Verify`.

Fix `downloads` directory not being created.

Fix detecting `P7Zip` from symbol.

docs/Formula-Cookbook: preach what we practise

Replaces our serialization of child process
errors via Marshal with JSON, preventing
unintentional or malicious code execution outside
of the build sandbox.

Additionally, adds tests for the new behavior.

cask: consistency and cleanliness renames.

Fix the load path, requires and some filenames accordingly.

Revert "Use JSON to marshal errors from children"

super/cc: fix -mmacosx-version-min on Mojave.

Remove some `#popen_read`s.