Add options to customize generated gemfiles (#191)

README.md

@@ -155,6 +155,46 @@ group :test do
 end
 ```
 
+Customization
+-------------
+
+It is possible to customize the generated Gemfiles by adding a `customize_gemfiles` block to
+your `Appraisals` file. The block must contain a hash of key/value pairs. Currently supported
+customizations include:
+- heading: a string that by default adds "# This file was generated by Appraisal" to the top of each Gemfile, (the string will be commented for you)
+- single_quotes: a boolean that controls if strings are single quoted in each Gemfile, defaults to false
+
+### Example Usage
+
+**Appraisals**
+```ruby
+customize_gemfiles do
+  {
+    single_quotes: true,
+    heading: <<~HEADING
+      frozen_string_literal: true
+
+      File has been generated by Appraisal, do NOT modify it directly!
+      See the conventions at https://example.com/
+    HEADING
+  }
+end
+
+appraise "rails-3" do
+  gem "rails", "3.2.14"
+end
+```
+
+Using the `Appraisals` file defined above, this is what the resulting `Gemfile` will look like:
+```ruby
+# frozen_string_literal: true
+
+# File has been generated by Appraisal, do NOT modify it directly!
+# See the conventions at https://example.com/
+
+gem 'rails', '3.2.14'
+```
+
 Version Control
 ---------------
 

lib/appraisal/appraisal.rb

@@ -1,5 +1,6 @@
 require 'appraisal/gemfile'
 require 'appraisal/command'
+require "appraisal/customize"
 require 'appraisal/utils'
 require 'fileutils'
 require 'pathname'
@@ -62,8 +63,8 @@ def git_source(*args, &block)
 
     def write_gemfile
       File.open(gemfile_path, "w") do |file|
-        signature = "# This file was generated by Appraisal"
-        file.puts([signature, gemfile.to_s].join("\n\n"))
+        signature = Customize.heading || "This file was generated by Appraisal"
+        file.puts([comment_lines(signature), quoted_gemfile].join("\n\n"))
       end
     end
 
@@ -171,5 +172,21 @@ def bundle_options(options)
 
       options_strings.join(" ") if options_strings != []
     end
+
+    def comment_lines(heading)
+      heading.lines.map do |line|
+        if line.lstrip.empty?
+          line
+        else
+          "# #{line}"
+        end
+      end.join
+    end
+
+    def quoted_gemfile
+      return gemfile.to_s unless Customize.single_quotes
+
+      gemfile.to_s.tr('"', "'")
+    end
   end
 end

lib/appraisal/appraisal_file.rb

@@ -1,4 +1,5 @@
 require 'appraisal/appraisal'
+require "appraisal/customize"
 require 'appraisal/errors'
 require 'appraisal/gemfile'
 
@@ -33,6 +34,10 @@ def appraise(name, &block)
       @appraisals << appraisal
     end
 
+    def customize_gemfiles(&_block)
+      Customize.new(yield)
+    end
+
     private
 
     def run(definitions)

lib/appraisal/customize.rb

@@ -0,0 +1,16 @@
+module Appraisal
+  class Customize
+    def initialize(heading: nil, single_quotes: false)
+      @@heading = heading
+      @@single_quotes = single_quotes
+    end
+
+    def self.heading
+      @@heading ||= nil
+    end
+
+    def self.single_quotes
+      @@single_quotes ||= false
+    end
+  end
+end

spec/appraisal/appraisal_spec.rb

@@ -28,6 +28,63 @@
     expect(output_file.read).to match(/[^\n]*\n\z/m)
   end
 
+  context "gemfile customization" do
+    it "generates a gemfile with a custom heading" do
+      heading = "This file was generated with a custom heading!"
+      Appraisal::Customize.new(heading: heading)
+      output_file = Tempfile.new("gemfile")
+      appraisal = Appraisal::Appraisal.new("custom", "Gemfile")
+      allow(appraisal).to receive(:gemfile_path).and_return(output_file.path)
+
+      appraisal.write_gemfile
+
+      expected_output = "# #{heading}"
+      expect(output_file.read).to start_with(expected_output)
+    end
+
+    it "generates a gemfile with multiple lines of custom heading" do
+      heading = <<~HEADING
+        frozen_string_literal: true\n
+        This file was generated with a custom heading!
+      HEADING
+      Appraisal::Customize.new(heading: heading)
+      output_file = Tempfile.new("gemfile")
+      appraisal = Appraisal::Appraisal.new("custom", "Gemfile")
+      allow(appraisal).to receive(:gemfile_path).and_return(output_file.path)
+
+      appraisal.write_gemfile
+
+      expected_output = <<~HEADING
+        # frozen_string_literal: true\n
+        # This file was generated with a custom heading!
+      HEADING
+      expect(output_file.read).to start_with(expected_output)
+    end
+
+    it "generates a gemfile with single quotes rather than doubles" do
+      Appraisal::Customize.new(single_quotes: true)
+      output_file = Tempfile.new("gemfile")
+      appraisal = Appraisal::Appraisal.new("quotes", 'gem "foo"')
+      allow(appraisal).to receive(:gemfile_path).and_return(output_file.path)
+
+      appraisal.write_gemfile
+
+      expect(output_file.read).to match(/gem 'foo'/)
+    end
+
+    it "does not customize anything by default" do
+      Appraisal::Customize.new
+      output_file = Tempfile.new("gemfile")
+      appraisal = Appraisal::Appraisal.new("fake", 'gem "foo"')
+      allow(appraisal).to receive(:gemfile_path).and_return(output_file.path)
+
+      appraisal.write_gemfile
+
+      expected_file = %(# This file was generated by Appraisal\n\ngem "foo"\n)
+      expect(output_file.read).to eq(expected_file)
+    end
+  end
+
   context 'parallel installation' do
     include StreamHelpers
 

spec/appraisal/customize_spec.rb

@@ -0,0 +1,18 @@
+require "spec_helper"
+require "appraisal/customize"
+
+describe Appraisal::Customize do
+  it "has defaults" do
+    expect(described_class.heading).to eq nil
+    expect(described_class.single_quotes).to eq false
+    expect { described_class.new }.to_not(change do
+      [described_class.heading, described_class.single_quotes]
+    end)
+  end
+
+  it "can override defaults" do
+    described_class.new(single_quotes: true, heading: "foo")
+    expect(described_class.heading).to eq "foo"
+    expect(described_class.single_quotes).to eq true
+  end
+end