Add hook option for configuring environment variables

Some command line utilities can only be configured via environment
variables. Add a hook option that allows you to set additional
environment variables that a hook should run with.

Author: sds

CHANGELOG.md

@@ -7,6 +7,8 @@
 * Fix handling of paths with spaces in the name
 * Fix `CaseConflicts` pre-commit hook to not fail on initial commit
 * Fix handling of files removed or renamed in a commit amendment
+* Add `env` hook configuration option that allows you to set values for
+  environment variables during the course of a particular hook's run
 
 ## 0.25.0
 

README.md

@@ -192,6 +192,7 @@ Option                                  | Description
 `required_library`/`required_libraries` | List of Ruby libraries to load with `Kernel.require` before the hook runs. This is specifically for hooks that integrate with external Ruby libraries.
 `command`                               | Array of arguments to use as the command. How each hook uses this is different, but it allows hooks to change the context with which they run. For example, you can change the command to be `['bundle', 'exec', 'rubocop']` instead of just `rubocop` so that you can use the gem versions specified in your local `Gemfile.lock`. This defaults to the name of the `required_executable`.
 `flags`                                 | Array of arguments to append to the `command`. This is useful for customizing the behavior of a tool. It's also useful when a newer version of a tool removes/renames existing flags, so you can update the flags via your `.overcommit.yml` instead of waiting for an upstream fix in Overcommit.
+`env`                                   | Hash of environment variables the hook should be run with. This is intended to be used as a last resort when an executable a hook runs is configured only via an environment variable. Any pre-existing environment variables with the same names as ones defined in `env` will have their original values restored after the hook runs.
 `install_command`                       | Command the user can run to install the `required_executable` (or alternately the specified `required_libraries`). This is intended for documentation purposes, as Overcommit does not install software on your behalf since there are too many edge cases where such behavior would result in incorrectly configured installations (e.g. installing a Python package in the global package space instead of in a virtual environment).
 
 In addition to the built-in configuration options, each hook can expose its

lib/overcommit/hook/base.rb

@@ -42,7 +42,8 @@ def run_and_transform
       if output = check_for_requirements
         status = :fail
       else
-        status, output = process_hook_return_value(run)
+        result = Overcommit::Utils.with_environment(@config.fetch('env', {})) { run }
+        status, output = process_hook_return_value(result)
       end
 
       [transform_status(status), output]

spec/overcommit/hook/base_spec.rb

@@ -0,0 +1,35 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::Base do
+  let(:config) { double('config') }
+  let(:context) { double('context') }
+  let(:hook) { described_class.new(config, context) }
+
+  describe '#run_and_transform' do
+    let(:var_name) { 'OVERCOMMIT_TEST_HOOK_VAR' }
+    let(:hook_config) { {} }
+
+    before do
+      config.stub(:for_hook).and_return(hook_config)
+      hook.stub(:run) { ENV[var_name] == 'pass' ? :pass : :fail }
+    end
+
+    subject { hook.run_and_transform }
+
+    context 'when no env configuration option is specified' do
+      let(:hook_config) { {} }
+
+      it 'does not modify the environment' do
+        subject.first.should == :fail
+      end
+    end
+
+    context 'when env configuration option is specified' do
+      let(:hook_config) { { 'env' => { var_name => 'pass' } } }
+
+      it 'does not modify the environment' do
+        subject.first.should == :pass
+      end
+    end
+  end
+end