Warn when attempting to pipe commands

The `execute` helper does not support piping commands due to the
complexity of supporting this in both MRI and JRuby implementations.

In order to prevent misuse, fail loudly to the user if they try to use
the pipe character as one of the arguments in their command.

Change-Id: Id87e3173a6cb4936c2f06733c688201c1a31dada
Reviewed-on: http://gerrit.causes.com/42170
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

CHANGELOG.md

@@ -8,6 +8,8 @@
   prevents Overcommit hooks from running
 * Fix bug that prevented RailsSchemaUpToDate from working in directories that
   contained decimals
+* Warn when trying to pipe commands using the `execute` helper, as this is not
+  supported
 
 ## 0.16.0
 

lib/overcommit/exceptions.rb

@@ -20,6 +20,10 @@ class HookLoadError < StandardError; end
   # Raised when a {HookRunner} could not be loaded.
   class HookContextLoadError < StandardError; end
 
+  # Raised when a pipe character is used in the `execute` helper, as this was
+  # likely used in error.
+  class InvalidCommandArgs < StandardError; end
+
   # Raised when an installation target is not a valid git repository.
   class InvalidGitRepo < StandardError; end
 

lib/overcommit/utils.rb

@@ -63,6 +63,11 @@ def in_path?(cmd)
       # specified in Overcommit's Gemfile--a nasty consequence of using
       # `bundle exec overcommit` while developing locally.
       def execute(args)
+        if args.include?('|')
+          raise Overcommit::Exceptions::InvalidCommandArgs,
+                'Cannot pipe commands with the `execute` helper'
+        end
+
         with_environment 'RUBYOPT' => nil do
           Subprocess.spawn(args)
         end

spec/overcommit/utils_spec.rb

@@ -68,4 +68,25 @@
 
     it { should =~ %w[CommitMsg PreCommit PostCheckout] }
   end
+
+  describe '.execute' do
+    let(:arguments) { %w[echo -n Hello World] }
+    subject { described_class.execute(arguments) }
+
+    it 'returns result with the output' do
+      subject.stdout.should == 'Hello World'
+    end
+
+    it 'returns result with the exit status' do
+      subject.status.should == 0
+    end
+
+    context 'when one of the arguments is a lone pipe character' do
+      let(:arguments) { %w[ps aux | grep bash] }
+
+      it 'raises an exception' do
+        expect { subject }.to raise_error Overcommit::Exceptions::InvalidCommandArgs
+      end
+    end
+  end
 end