Auto merge of #5704 - bundler:colby/init-new-gemfile-format, r=segiddins

generate gems.rb in bundle init with feature flag

This PR adds a feature flag to generate a new `gems.rb` with `bundle init`.

7 files changed, 86 insertions, 7 deletions

diff --git a/lib/bundler/cli/init.rb b/lib/bundler/cli/init.rb
index 8ffd1db41a..16330f6c6d 100644
--- a/lib/bundler/cli/init.rb
+++ b/lib/bundler/cli/init.rb
@@ -7,8 +7,8 @@ module Bundler
     end
 
     def run
-      if File.exist?("Gemfile")
-        Bundler.ui.error "Gemfile already exists at #{SharedHelpers.pwd}/Gemfile"
+      if File.exist?(gemfile)
+        Bundler.ui.error "#{gemfile} already exists at #{SharedHelpers.pwd}/#{gemfile}"
         exit 1
       end
 
@@ -21,15 +21,21 @@ module Bundler
 
         spec = Bundler.load_gemspec_uncached(gemspec)
 
-        puts "Writing new Gemfile to #{SharedHelpers.pwd}/Gemfile"
-        File.open("Gemfile", "wb") do |file|
+        File.open(gemfile, "wb") do |file|
           file << "# Generated from #{gemspec}\n"
           file << spec.to_gemfile
         end
       else
-        puts "Writing new Gemfile to #{SharedHelpers.pwd}/Gemfile"
-        FileUtils.cp(File.expand_path("../../templates/Gemfile", __FILE__), "Gemfile")
+        FileUtils.cp(File.expand_path("../../templates/#{gemfile}", __FILE__), gemfile)
       end
+
+      puts "Writing new #{gemfile} to #{SharedHelpers.pwd}/#{gemfile}"
+    end
+
+  private
+
+    def gemfile
+      @gemfile ||= Bundler.feature_flag.init_gems_rb? ? "gems.rb" : "Gemfile"
     end
   end
 end
diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index 5ee69f538c..3a4353f2af 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -18,6 +18,7 @@ module Bundler
     settings_flag(:only_update_to_newer_versions) { bundler_2_mode? }
     settings_flag(:plugins) { @bundler_version >= Gem::Version.new("1.14") }
     settings_flag(:error_on_stderr) { bundler_2_mode? }
+    settings_flag(:init_gems_rb) { bundler_2_mode? }
 
     def initialize(bundler_version)
       @bundler_version = Gem::Version.create(bundler_version)
diff --git a/lib/bundler/settings.rb b/lib/bundler/settings.rb
index 68a7add942..7857e00ea0 100644
--- a/lib/bundler/settings.rb
+++ b/lib/bundler/settings.rb
@@ -16,18 +16,19 @@ module Bundler
       disable_local_branch_check
       disable_shared_gems
       disable_version_check
+      error_on_stderr
       force_ruby_platform
       frozen
       gem.coc
       gem.mit
       ignore_messages
+      init_gems_rb
       major_deprecations
       no_install
       no_prune
       only_update_to_newer_versions
       plugins
       silence_root_warning
-      error_on_stderr
     ].freeze
 
     NUMBER_KEYS = %w[
diff --git a/lib/bundler/templates/gems.rb b/lib/bundler/templates/gems.rb
new file mode 100644
index 0000000000..a6ef23ba3e
--- /dev/null
+++ b/lib/bundler/templates/gems.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+# A sample gems.rb
+source "https://rubygems.org"
+
+# gems "rails"
diff --git a/man/bundle-config.ronn b/man/bundle-config.ronn
index b7ae07698c..18773017f8 100644
--- a/man/bundle-config.ronn
+++ b/man/bundle-config.ronn
@@ -224,6 +224,8 @@ learn more about their operation in [bundle install(1)][bundle-install].
    command with a private gemstash server.
 * `error_on_stderr` (`BUNDLE_ERROR_ON_STDERR`)
    Print Bundler errors to stderr
+* `init_gems_rb` (`BUNDLE_NEW_GEMFILE_NAME`)
+   generate a new gems.rb on `bundle init` instead of the `Gemfile`
 
 In general, you should set these settings per-application by using the applicable
 flag to the [bundle install(1)][bundle-install] or [bundle package(1)][bundle-package] command.
diff --git a/spec/commands/init_spec.rb b/spec/commands/init_spec.rb
index 6bbbfa8c96..7be379b510 100644
--- a/spec/commands/init_spec.rb
+++ b/spec/commands/init_spec.rb
@@ -6,6 +6,11 @@ RSpec.describe "bundle init" do
     expect(bundled_app("Gemfile")).to exist
   end
 
+  it "prints a message to the user" do
+    bundle :init
+    expect(out).to include("Writing new Gemfile")
+  end
+
   context "when a Gemfile already exists" do
     before do
       gemfile <<-G
@@ -62,4 +67,62 @@ RSpec.describe "bundle init" do
       end
     end
   end
+
+  context "when init_gems_rb setting is enabled" do
+    before { bundle "config init_gems_rb true" }
+
+    it "generates a gems.rb file" do
+      bundle :init
+      expect(bundled_app("gems.rb")).to exist
+    end
+
+    context "when gems.rb already exists" do
+      before do
+        create_file("gems.rb", <<-G)
+          gem "rails"
+        G
+      end
+
+      it "does not change existing Gemfiles" do
+        expect { bundle :init }.not_to change { File.read(bundled_app("gems.rb")) }
+      end
+
+      it "notifies the user that an existing gems.rb already exists" do
+        bundle :init
+        expect(out).to include("gems.rb already exists")
+      end
+    end
+
+    context "given --gemspec option" do
+      let(:spec_file) { tmp.join("test.gemspec") }
+
+      before do
+        File.open(spec_file, "w") do |file|
+          file << <<-S
+            Gem::Specification.new do |s|
+            s.name = 'test'
+            s.add_dependency 'rack', '= 1.0.1'
+            s.add_development_dependency 'rspec', '1.2'
+            end
+          S
+        end
+      end
+
+      it "should generate from an existing gemspec" do
+        bundle :init, :gemspec => spec_file
+
+        gemfile = bundled_app("gems.rb").read
+        expect(gemfile).to match(%r{source 'https://rubygems.org'})
+        expect(gemfile.scan(/gem "rack", "= 1.0.1"/).size).to eq(1)
+        expect(gemfile.scan(/gem "rspec", "= 1.2"/).size).to eq(1)
+        expect(gemfile.scan(/group :development/).size).to eq(1)
+      end
+
+      it "prints message to user" do
+        bundle :init, :gemspec => spec_file
+
+        expect(out).to include("Writing new gems.rb")
+      end
+    end
+  end
 end
diff --git a/spec/quality_spec.rb b/spec/quality_spec.rb
index 5f55f123e2..db019e03de 100644
--- a/spec/quality_spec.rb
+++ b/spec/quality_spec.rb
@@ -244,6 +244,7 @@ RSpec.describe "The library itself" do
         bundler/capistrano.rb
         bundler/gem_tasks.rb
         bundler/vlad.rb
+        bundler/templates/gems.rb
       ]
       lib_files = `git ls-files -z`.split("\x0").grep(/\.rb$/) - exclusions
       lib_files.reject! {|f| f.start_with?("bundler/vendor") }