Add --force flag to always overwrite hooks

If a user attempted to install Overcommit hooks into a git repository
that already had non-overcommit hooks, it would report an error. Allow
the user to specify a `--force` flag which disables this error and
ensures the hooks are installed, overwriting if necessary.

Closes sds#7

Change-Id: I9390e5e122572444202f0b1ef8ae172a15c5b4dc
Reviewed-on: http://gerrit.causes.com/36004
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>

Author: Shane da Silva

CHANGELOG.md

@@ -8,6 +8,8 @@
 * Add support for JRuby 1.7.9 in Ruby 1.9 mode
 * Display more helpful error message when installing Overcommit into a repo
   that already has non-Overcommit hooks
+* Add `--force` flag allowing Overcommit to be installed in repositories that
+  already contain non-Overcommit hooks (overwriting them in the process)
 
 ## 0.6.3
 

README.md

@@ -90,6 +90,7 @@ Command Line Flag         | Description
 --------------------------|----------------------------------------------------
 `-i`/`--install`          | Install Overcommit hooks in a repository
 `-u`/`--uninstall`        | Remove Overcommit hooks from a repository
+`-f`/`--force`            | Don't bail on install if other hooks already exist--overwrite them
 `-t`/`--template-dir`     | Print location of template directory
 `-h`/`--help`             | Show command-line flag documentation
 `-v`/`--version`          | Show version

lib/overcommit/cli.rb

@@ -45,6 +45,10 @@ def parse_arguments
           @options[:action] = :install
         end
 
+        opts.on('-f', '--force', 'Overwrite any previously installed hooks') do
+          @options[:force] = true
+        end
+
         opts.on('-t', '--template-dir', 'Print location of template directory') do
           @options[:action] = :template_dir
         end

spec/overcommit/installer_spec.rb

@@ -81,6 +81,13 @@
             it 'does not raise an error' do
               expect { subject }.to_not raise_error
             end
+
+            it 'symlinks all supported hooks to the master hook' do
+              subject
+              Overcommit::Utils.supported_hook_types.all? do |hook_type|
+                File.readlink(File.join(hooks_dir, hook_type)) == 'overcommit-hook'
+              end
+            end
           end
         end
       end