✨ Support eval_gemfile

- Fixes thoughtbot#154

README.md

@@ -110,6 +110,90 @@ When you prefix a command with `appraisal`, the command is run with the
 appropriate Gemfile for that appraisal, ensuring the correct dependencies
 are used.
 
+Sharing Modular Gemfiles between Appraisals
+-------
+
+_New for version 3.0_
+
+It is common for Appraisals to duplicate sets of gems, and sometimes it
+makes sense to DRY this up into a shared, modular, gemfile.
+In a scenario where you do not load your main Gemfile in your Appraisals,
+but you want to declare your various gem sets for e.g.
+`%w(coverage test documentation audit)` once each, you can re-use the same
+modular gemfiles for local development by referencing them from the main
+Gemfile.
+
+To do this, use the `eval_gemfile` declaration within the necessary
+`appraise` block in your `Appraisals` file, which will behave the same as
+`eval_gemfile` does in a normal Gemfile.
+
+### Example Usage
+
+You could put your modular gemfiles in the `gemfiles` directory, or nest
+them in `gemfiles/modular/*`, which will be used for this example.
+
+**Gemfile**
+```ruby
+eval_gemfile "gemfiles/modular/audit.gemfile"
+```
+
+**gemfiles/modular/audit.gemfile**
+```ruby
+# Many gems are dropping support for Ruby < 3.1,
+#   so we only want to run our security audit in CI on Ruby 3.1+
+gem "bundler-audit", "~> 0.9.2"
+# And other security audit gems...
+```
+
+**Appraisals**
+```ruby
+appraise "ruby-2-7" do
+  gem "dummy"
+end
+
+appraise "ruby-3-0" do
+  gem "dummy"
+end
+
+appraise "ruby-3-1" do
+  gem "dummy"
+  eval_gemfile "modular/audit.gemfile"
+end
+
+appraise "ruby-3-2" do
+  gem "dummy"
+  eval_gemfile "modular/audit.gemfile"
+end
+
+appraise "ruby-3-3" do
+  gem "dummy"
+  eval_gemfile "modular/audit.gemfile"
+end
+
+appraise "ruby-3-4" do
+  gem "dummy"
+  eval_gemfile "modular/audit.gemfile"
+end
+```
+
+**Appraisal.root.gemfile**
+```ruby
+source "https://rubygems.org"
+
+# Appraisal Root Gemfile is for running appraisal to generate the Appraisal Gemfiles
+# We do not load the standard Gemfile, as it is tailored for local development,
+#   while appraisals are tailored for CI.
+
+gemspec
+
+gem "appraisal"
+```
+
+Now when you need to update your appraisals:
+```shell
+BUNDLE_GEMFILE=Appraisal.root.gemfile bundle exec appraisal update
+```
+
 Removing Gems using Appraisal
 -------
 

lib/appraisal/appraisal.rb

@@ -19,6 +19,10 @@ def initialize(name, source_gemfile)
       @gemfile = source_gemfile.dup
     end
 
+    def eval_gemfile(*args)
+      gemfile.eval_gemfile(*args)
+    end
+
     def gem(*args)
       gemfile.gem(*args)
     end

lib/appraisal/bundler_dsl.rb

@@ -18,6 +18,7 @@ class BundlerDSL
       source_blocks
       install_if
       gemspec
+      eval_gemfile
     ]
 
     def initialize
@@ -32,12 +33,17 @@ def initialize
       @source_blocks = OrderedHash.new
       @git_sources = {}
       @install_if = {}
+      @eval_gemfile = []
     end
 
     def run(&block)
       instance_exec(&block)
     end
 
+    def eval_gemfile(path, contents = nil)
+      @eval_gemfile << [path, contents]
+    end
+
     def gem(name, *requirements)
       @dependencies.add(name, substitute_git_source(requirements))
     end
@@ -114,6 +120,12 @@ def git_source(source, &block)
 
     private
 
+    def eval_gemfile_entry
+      @eval_gemfile.map { |(p, c)| "eval_gemfile(#{p.inspect}#{", #{c.inspect}" if c})" } * "\n\n"
+    end
+
+    alias_method :eval_gemfile_entry_for_dup, :eval_gemfile_entry
+
     def source_entry
       @sources.uniq.map { |source| "source #{source.inspect}" }.join("\n")
     end

spec/acceptance/eval_gemfile_spec.rb

@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe "eval_gemfile" do
+  before do
+    build_appraisal_file
+    build_modular_gemfile
+    build_rakefile
+    build_gemspec
+  end
+
+  it "supports eval_gemfile syntax" do
+    write_file "Gemfile", <<-GEMFILE
+      source "https://rubygems.org"
+
+      gem 'appraisal', :path => #{PROJECT_ROOT.inspect}
+
+      gemspec
+    GEMFILE
+
+    run "bundle install --local"
+    run "appraisal install"
+    output = run "appraisal rake version"
+
+    expect(output).to include "Loaded 1.1.0"
+  end
+
+  def build_modular_gemfile
+    begin
+      Dir.mkdir("tmp/stage/gemfiles")
+    rescue
+      nil
+    end
+
+    write_file File.join("gemfiles", "im_with_dummy"), <<-GEMFILE
+      # No source needed because this is a modular gemfile intended to be loaded into another gemfile,
+      #   which will define source.
+      gem 'dummy'
+    GEMFILE
+  end
+
+  def build_appraisal_file
+    super(<<-APPRAISALS)
+      appraise 'stock' do
+        gem 'rake'
+        eval_gemfile "im_with_dummy"
+      end
+    APPRAISALS
+  end
+
+  def build_rakefile
+    write_file "Rakefile", <<-RAKEFILE
+      require 'rubygems'
+      require 'bundler/setup'
+      require 'appraisal'
+
+      task :version do
+        require 'dummy'
+        puts "Loaded \#{$dummy_version}"
+      end
+    RAKEFILE
+  end
+
+  def build_gemspec(path = ".")
+    begin
+      Dir.mkdir("tmp/stage/#{path}")
+    rescue
+      nil
+    end
+
+    write_file File.join(path, "gemspec_project.gemspec"), <<-GEMSPEC
+      Gem::Specification.new do |s|
+        s.name = 'gemspec_project'
+        s.version = '0.1'
+        s.summary = 'Awesome Gem!'
+        s.authors = "Appraisal"
+      end
+    GEMSPEC
+  end
+end