Auto merge of #5920 - bundler:colby/bundler-list, r=segiddins

implement new list command

### What was the end-user problem that led to this PR?

We're removing the `bundle show` command (which has been replaced with `bundle info`) but we should probably still have a command to list the gems in the bundle.

### What was your diagnosis of the problem?

`bundle show` has been marked as deprecated but a replacement for listing gems does not yet exist

### What is your fix for the problem, implemented in this PR?

Add a new `bundle list` (including `ls` alias) that prints the gems in the bundle, this was taken from #4754

4 files changed, 37 insertions, 1 deletions

diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 0d559a8f76..2adbac403e 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -261,7 +261,19 @@ module Bundler
       Show.new(options, gem_name).run
     end
     # TODO: 2.0 remove `bundle show`
-    map %w[list] => "show"
+
+    if Bundler.feature_flag.list_command?
+      desc "list", "List all gems in the bundle"
+      method_option "name-only", :type => :boolean, :banner => "print only the gem names"
+      def list
+        require "bundler/cli/list"
+        List.new(options).run
+      end
+
+      map %w[ls] => "list"
+    else
+      map %w[list] => "show"
+    end
 
     desc "info GEM [OPTIONS]", "Show information for the given gem"
     method_option "path", :type => :boolean, :banner => "Print full path to gem"
diff --git a/lib/bundler/cli/list.rb b/lib/bundler/cli/list.rb
new file mode 100644
index 0000000000..b5e7c1e650
--- /dev/null
+++ b/lib/bundler/cli/list.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Bundler
+  class CLI::List
+    def initialize(options)
+      @options = options
+    end
+
+    def run
+      specs = Bundler.load.specs.reject {|s| s.name == "bundler" }.sort_by(&:name)
+      return specs.each {|s| Bundler.ui.info s.name } if @options["name-only"]
+
+      return Bundler.ui.info "No gems in the Gemfile" if specs.empty?
+      Bundler.ui.info "Gems included by the bundle:"
+      specs.each do |s|
+        Bundler.ui.info "  * #{s.name} (#{s.version}#{s.git_version})"
+      end
+
+      Bundler.ui.info "Use `bundle info` to print more detailed information about a gem"
+    end
+  end
+end
diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index 39e2be978c..07d11418be 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -49,6 +49,7 @@ module Bundler
     settings_flag(:unlock_source_unlocks_spec) { !bundler_2_mode? }
     settings_flag(:update_requires_all_flag) { bundler_2_mode? }
     settings_flag(:default_install_uses_path) { bundler_2_mode? }
+    settings_flag(:list_command) { bundler_2_mode? }
 
     settings_option(:default_cli_command) { bundler_2_mode? ? :cli_help : :install }
 
diff --git a/lib/bundler/settings.rb b/lib/bundler/settings.rb
index fc59631608..a23264ecf4 100644
--- a/lib/bundler/settings.rb
+++ b/lib/bundler/settings.rb
@@ -34,6 +34,7 @@ module Bundler
       global_gem_cache
       ignore_messages
       init_gems_rb
+      list_command
       lockfile_uses_separate_rubygems_sources
       major_deprecations
       no_install