Add explicit source when available in the error msg upon failure

The error-message function did not provide an explicit source,
and that could lead in some confusion especially with big Gemfiles.

The command that is output, should be valid.

3 files changed, 43 insertions, 5 deletions

diff --git a/lib/bundler/installer/gem_installer.rb b/lib/bundler/installer/gem_installer.rb
index 086b763d20..a38f8d95be 100644
--- a/lib/bundler/installer/gem_installer.rb
+++ b/lib/bundler/installer/gem_installer.rb
@@ -44,7 +44,12 @@ module Bundler
     end
 
     def gem_install_message
-      "Make sure that `gem install #{spec.name} -v '#{spec.version}'` succeeds before bundling."
+      remotes = spec.source.remotes
+      if remotes.size == 1
+        "Make sure that `gem install #{spec.name} -v '#{spec.version}' --source '#{remotes.first}'` succeeds before bundling."
+      else
+        "Make sure that `gem install #{spec.name} -v '#{spec.version}'` succeeds before bundling."
+      end
     end
 
     def spec_settings
diff --git a/spec/commands/install_spec.rb b/spec/commands/install_spec.rb
index 4cb8584633..b6e89d70da 100644
--- a/spec/commands/install_spec.rb
+++ b/spec/commands/install_spec.rb
@@ -348,14 +348,14 @@ RSpec.describe "bundle install with gem sources" do
       end
 
       install_gemfile <<-G, :full_index => true
-        source "file://#{gem_repo2}"
+        source "file:\/\/localhost#{gem_repo2}"
 
         gem "ajp-rails", "0.0.0"
       G
 
       expect(last_command.stdboth).not_to match(/Error Report/i)
       expect(last_command.bundler_err).to include("An error occurred while installing ajp-rails (0.0.0), and Bundler cannot continue.").
-        and include("Make sure that `gem install ajp-rails -v '0.0.0'` succeeds before bundling.")
+        and include("Make sure that `gem install ajp-rails -v '0.0.0' --source 'file://localhost#{gem_repo2}/'` succeeds before bundling.")
     end
 
     it "doesn't blow up when the local .bundle/config is empty" do
diff --git a/spec/install/failure_spec.rb b/spec/install/failure_spec.rb
index 44006be52e..27abe9fcc3 100644
--- a/spec/install/failure_spec.rb
+++ b/spec/install/failure_spec.rb
@@ -15,12 +15,45 @@ RSpec.describe "bundle install" do
       end
 
       install_gemfile <<-G
-        source "file:#{gem_repo2}"
+        source "file:\/\/localhost#{gem_repo2}"
         gem "rails"
       G
       expect(last_command.bundler_err).to end_with(<<-M.strip)
 An error occurred while installing activesupport (2.3.2), and Bundler cannot continue.
-Make sure that `gem install activesupport -v '2.3.2'` succeeds before bundling.
+Make sure that `gem install activesupport -v '2.3.2' --source 'file://localhost#{gem_repo2}/'` succeeds before bundling.
+
+In Gemfile:
+  rails was resolved to 2.3.2, which depends on
+    actionmailer was resolved to 2.3.2, which depends on
+      activesupport
+                     M
+    end
+
+    it "prints out the hint for the remote source when available" do
+      build_repo2 do
+        build_gem "activesupport", "2.3.2" do |s|
+          s.extensions << "Rakefile"
+          s.write "Rakefile", <<-RUBY
+            task :default do
+              abort "make installing activesupport-2.3.2 fail"
+            end
+          RUBY
+        end
+      end
+
+      build_repo4 do
+        build_gem "a"
+      end
+
+      install_gemfile <<-G
+        source "file:\/\/localhost#{gem_repo4}"
+        source "file:\/\/localhost#{gem_repo2}" do
+          gem "rails"
+        end
+      G
+      expect(last_command.bundler_err).to end_with(<<-M.strip)
+An error occurred while installing activesupport (2.3.2), and Bundler cannot continue.
+Make sure that `gem install activesupport -v '2.3.2' --source 'file://localhost#{gem_repo2}/'` succeeds before bundling.
 
 In Gemfile:
   rails was resolved to 2.3.2, which depends on