Add informational message when default_cli_command is unset.

Author: hsbt

bundler/lib/bundler/cli.rb

@@ -131,6 +131,16 @@ def install_or_cli_help
     def self.default_command(meth = nil)
       return super if meth
 
+      unless Bundler.settings[:default_cli_command]
+        Bundler.ui.info <<-MSG
+          In the feature version of Bundler, running `bundle` without argument will no longer run `bundle install`.
+          Instead, the `cli_help` command will be displayed. Please use `bundle install` explicitly for scripts like CI/CD.
+          If you wish to use feature behavior now with `bundle config set default_cli_command cli_help --global`
+          or you can continue to use the old behavior with `bundle config set default_cli_command install_or_cli_help --global`.
+          This message will be removed after a default_cli_command value is set.
+        MSG
+      end
+
       Bundler.settings[:default_cli_command] || "install_or_cli_help"
     end
 

bundler/spec/bundler/cli_spec.rb

@@ -90,13 +90,21 @@ def out_with_macos_man_workaround
     it "tries to installs by default but print help on missing Gemfile" do
       bundle "", raise_on_error: false
       expect(err).to include("Could not locate Gemfile")
+      expect(out).to include("In the feature version of Bundler")
 
       expect(out).to include("Bundler version #{Bundler::VERSION}").
         and include("\n\nBundler commands:\n\n").
         and include("\n\n  Primary commands:\n").
         and include("\n\n  Utilities:\n").
         and include("\n\nOptions:\n")
     end
+
+    it "runs bundle install when default_cli_command set to install" do
+      bundle "config set default_cli_command install_or_cli_help"
+      bundle "", raise_on_error: false
+      expect(out).to_not include("In the feature version of Bundler")
+      expect(err).to include("Could not locate Gemfile")
+    end
   end
 
   context "when ENV['BUNDLE_GEMFILE'] is set to an empty string" do