Auto merge of #6676 - ankitkataria:gemfile-flag, r=colby-swandale

Add gemfile flag to exec command

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

This PR resolves the issue #5924

### What was your diagnosis of the problem?

- added a `gemfile` flag in `cli.rb`
- if `options[:gemfile]` is set I created a SharedHelper method `custom_gemfile` which used the predefined `find_file` function to find and set the environment variable with the argument provided

(cherry picked from commit c4892480aba36d31a3b6e232f17a705aaad1b730)

2 files changed, 10 insertions, 0 deletions

diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 19d605f971..706c0b90dc 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -423,6 +423,7 @@ module Bundler
 
     desc "exec [OPTIONS]", "Run the command in context of the bundle"
     method_option :keep_file_descriptors, :type => :boolean, :default => false
+    method_option :gemfile, :type => :string, :required => false
     long_desc <<-D
       Exec runs a command, providing it access to the gems in the bundle. While using
       bundle exec you can require and call the bundled gems as if they were installed
diff --git a/spec/commands/exec_spec.rb b/spec/commands/exec_spec.rb
index 03212fd9b3..bd3c49baa1 100644
--- a/spec/commands/exec_spec.rb
+++ b/spec/commands/exec_spec.rb
@@ -6,6 +6,15 @@ RSpec.describe "bundle exec" do
     system_gems(system_gems_to_install, :path => :bundle_path)
   end
 
+  it "works with --gemfile flag" do
+    create_file "CustomGemfile", <<-G
+      gem "rack", "1.0.0"
+    G
+
+    bundle "exec --gemfile CustomGemfile rackup"
+    expect(out).to eq("1.0.0")
+  end
+
   it "activates the correct gem" do
     gemfile <<-G
       gem "rack", "0.9.1"