[rubygems/rubygems] Introduce bundle config set version feature

https://github.com/rubygems/rubygems/commit/c431a1df52

lib/bundler/man/bundle-config.1

@@ -299,6 +299,9 @@ The following is a list of all configuration keys and their purpose\. You can le
 \fBuser_agent\fR (\fBBUNDLE_USER_AGENT\fR): The custom user agent fragment Bundler includes in API requests\.
 .
 .IP "\(bu" 4
+\fBversion\fR (\fBBUNDLE_VERSION\fR): The version of Bundler to use when running under Bundler environment\. Defaults to \fBlocal\fR\. You can also specify \fBglobal\fR or \fBx\.y\.z\fR\. \fBlocal\fR will use the Bundler version specified in the \fBGemfile\.lock\fR, \fBglobal\fR will use the system version of Bundler, and \fBx\.y\.z\fR will use the specified version of Bundler\.
+.
+.IP "\(bu" 4
 \fBwith\fR (\fBBUNDLE_WITH\fR): A \fB:\fR\-separated list of groups whose gems bundler should install\.
 .
 .IP "\(bu" 4

lib/bundler/man/bundle-config.1.ronn

@@ -277,6 +277,12 @@ learn more about their operation in [bundle install(1)](bundle-install.1.html).
    and disallow passing no options to `bundle update`.
 * `user_agent` (`BUNDLE_USER_AGENT`):
    The custom user agent fragment Bundler includes in API requests.
+* `version` (`BUNDLE_VERSION`):
+   The version of Bundler to use when running under Bundler environment.
+   Defaults to `local`. You can also specify `global` or `x.y.z`.
+   `local` will use the Bundler version specified in the `Gemfile.lock`,
+   `global` will use the system version of Bundler, and `x.y.z` will use
+   the specified version of Bundler.
 * `with` (`BUNDLE_WITH`):
    A `:`-separated list of groups whose gems bundler should install.
 * `without` (`BUNDLE_WITHOUT`):

lib/bundler/self_manager.rb

@@ -15,11 +15,23 @@ module Bundler
     def install_locked_bundler_and_restart_with_it_if_needed
       return unless needs_switching?
 
-      Bundler.ui.info \
-        "Bundler #{current_version} is running, but your lockfile was generated with #{lockfile_version}. " \
-        "Installing Bundler #{lockfile_version} and restarting using that version."
+      begin
+        # BUNDLE_VERSION=x.y.z
+        restart_version = Gem::Version.new(Bundler.settings[:version])
 
-      install_and_restart_with(lockfile_version)
+        Bundler.ui.info \
+          "Bundler #{current_version} is running, but your configuration was #{restart_version}. " \
+          "Installing Bundler #{restart_version} and restarting using that version."
+      rescue ArgumentError
+        # BUNDLE_VERSION=local
+        restart_version = lockfile_version
+
+        Bundler.ui.info \
+          "Bundler #{current_version} is running, but your lockfile was generated with #{restart_version}. " \
+          "Installing Bundler #{restart_version} and restarting using that version."
+      end
+
+      install_and_restart_with(restart_version)
     end
 
     def update_bundler_and_restart_with_it_if_needed(target)
@@ -79,7 +91,8 @@ module Bundler
       autoswitching_applies? &&
         released?(lockfile_version) &&
         !running?(lockfile_version) &&
-        !updating?
+        !updating? &&
+        Bundler.settings[:version] != "global"
     end
 
     def autoswitching_applies?

lib/bundler/settings.rb

@@ -75,6 +75,7 @@ module Bundler
       shebang
       system_bindir
       trust-policy
+      version
     ].freeze
 
     DEFAULT_CONFIG = {
@@ -84,6 +85,7 @@ module Bundler
       "BUNDLE_REDIRECT" => 5,
       "BUNDLE_RETRY" => 3,
       "BUNDLE_TIMEOUT" => 10,
+      "BUNDLE_VERSION" => "local",
     }.freeze
 
     def initialize(root = nil)

spec/bundler/runtime/self_management_spec.rb

@@ -103,6 +103,25 @@ RSpec.describe "Self management", :rubygems => ">= 3.3.0.dev", :realworld => tru
       expect(out).to eq(Bundler::VERSION[0] == "2" ? "Bundler version #{Bundler::VERSION}" : Bundler::VERSION)
     end
 
+    it "installs BUNDLE_VERSION version when using bundle config version x.y.z" do
+      lockfile_bundled_with(Bundler::VERSION.gsub(/\.dev/, ""))
+
+      bundle "config set --local version #{previous_minor}"
+      bundle "install", :artifice => "vcr"
+      expect(out).to include("Bundler #{Bundler::VERSION} is running, but your configuration was #{previous_minor}. Installing Bundler #{previous_minor} and restarting using that version.")
+    end
+
+    it "does not try to install when using bundle config version global" do
+      lockfile_bundled_with(previous_minor)
+
+      bundle "config set version global"
+      bundle "install", :artifice => "vcr"
+      expect(out).not_to match(/restarting using that version/)
+
+      bundle "-v"
+      expect(out).to eq(Bundler::VERSION[0] == "2" ? "Bundler version #{Bundler::VERSION}" : Bundler::VERSION)
+    end
+
     private
 
     def lockfile_bundled_with(version)