Add JsonSyntax pre-commit

Change-Id: I071ccc85f3968f38e2ce8797551c47aaff048d31
Reviewed-on: http://gerrit.causes.com/37957
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>

Author: jfelchner

config/default.yml

@@ -91,6 +91,10 @@ PreCommit:
     description: 'Analyzing with JSHint'
     include: '**/*.js'
 
+  JsonSyntax:
+    description: 'Validating JSON syntax'
+    include: '**/*.json'
+
   JsxHint:
     description: 'Analyzing with JSXHint'
     include: '**/*.jsx'

lib/overcommit/hook/pre_commit/json_syntax.rb

@@ -0,0 +1,22 @@
+require 'json'
+
+module Overcommit::Hook::PreCommit
+  # Checks the syntax of any modified JSON files.
+  class JsonSyntax < Base
+    def run
+      output = []
+
+      applicable_files.each do |file|
+        begin
+          File.open(file) { |io| JSON.load(io) }
+        rescue JSON::ParserError => e
+          output << "#{e.message} parsing #{file}"
+        end
+      end
+
+      return :good if output.empty?
+
+      [:bad, output]
+    end
+  end
+end

overcommit.gemspec

@@ -27,6 +27,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 1.8.7'
 
   s.add_dependency             'childprocess', '>= 0.5.1'
+  s.add_dependency             'json', '>= 1.8' # For 1.8.7. support only
 
   s.add_development_dependency 'rspec', '2.14.1'
   s.add_development_dependency 'image_optim', '~> 0.13.0'

spec/overcommit/hook/pre_commit/json_syntax_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::PreCommit::JsonSyntax do
+  let(:config)      { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context)     { double('context') }
+  let(:staged_file) { 'my_file.json' }
+
+  subject           { described_class.new(config, context) }
+
+  before do
+    subject.stub(:applicable_files).and_return([staged_file])
+  end
+
+  around do |example|
+    repo do
+      File.open(staged_file, 'w') { |f| f.write('foo') }
+      `git add #{staged_file}`
+
+      example.run
+    end
+  end
+
+  context 'when JSON files have no errors' do
+    before do
+      JSON.stub(:load)
+    end
+
+    it { should pass }
+  end
+
+  context 'when JSON file has errors' do
+    before do
+      JSON.stub(:load).and_raise(JSON::ParserError)
+    end
+
+    it { should fail_hook }
+  end
+end