[PostitTrampoline] Automatically enable when target version is >= 2seg-enable-trampoline-2.0

4 files changed, 35 insertions, 14 deletions

diff --git a/exe/bundle b/exe/bundle
index 51a9035d97..ec88ea7552 100755
--- a/exe/bundle
+++ b/exe/bundle
@@ -4,12 +4,10 @@
 # Exit cleanly from an early interrupt
 Signal.trap("INT") { exit 1 }
 
-unless ENV["BUNDLE_DISABLE_POSTIT"]
-  update = "update".start_with?(ARGV.first || " ") && ARGV.find {|a| a.start_with?("--bundler") }
-  update &&= update =~ /--bundler(?:=(.+))?/ && $1 || "> 0.a"
-  ENV["BUNDLER_VERSION"] = update if update
-  require "bundler/postit_trampoline"
-end
+update = "update".start_with?(ARGV.first || " ") && ARGV.find {|a| a.start_with?("--bundler") }
+update &&= update =~ /--bundler(?:=(.+))?/ && $1 || "> 0.a"
+ENV["BUNDLER_VERSION"] = update if update
+require "bundler/postit_trampoline"
 
 require "bundler"
 # Check if an older version of bundler is installed
diff --git a/lib/bundler/postit_trampoline.rb b/lib/bundler/postit_trampoline.rb
index dbb23aa4d9..2a22489954 100644
--- a/lib/bundler/postit_trampoline.rb
+++ b/lib/bundler/postit_trampoline.rb
@@ -1,13 +1,18 @@
 # frozen_string_literal: true
-if ENV["BUNDLE_ENABLE_TRAMPOLINE"]
 
-  module BundlerVendoredPostIt; end
-  require "bundler/vendor/postit/lib/postit"
-  require "rubygems"
+module BundlerVendoredPostIt; end
+require "bundler/vendor/postit/lib/postit"
+require "rubygems"
 
-  environment = BundlerVendoredPostIt::PostIt::Environment.new([])
-  version = Gem::Requirement.new(environment.bundler_version)
+environment = BundlerVendoredPostIt::PostIt::Environment.new([])
+version = Gem::Requirement.new(environment.bundler_version)
+if version.requirements.size == 1 && version.requirements.first.first == "=" # version.exact?
+  if version.requirements.first.last.segments.first >= 2
+    ENV["BUNDLE_ENABLE_TRAMPOLINE"] = "true"
+  end
+end
 
+if ENV["BUNDLE_ENABLE_TRAMPOLINE"] && !ENV["BUNDLE_DISABLE_POSTIT"]
   installed_version =
     if defined?(Bundler::VERSION)
       Bundler::VERSION
@@ -65,4 +70,4 @@ You're running Bundler #{installed_version} but this project uses #{running_vers
     abort "The running bundler (#{running_version}) does not match the required `#{version}`"
   end
 
-end # unless ENV["BUNDLE_ENABLE_TRAMPOLINE"]
+end # if ENV["BUNDLE_ENABLE_TRAMPOLINE"] && !ENV["BUNDLE_DISABLE_POSTIT"]
diff --git a/lib/bundler/setup.rb b/lib/bundler/setup.rb
index 8b4b479778..4e213beed3 100644
--- a/lib/bundler/setup.rb
+++ b/lib/bundler/setup.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
-require "bundler/postit_trampoline" unless ENV["BUNDLE_DISABLE_POSTIT"]
+require "bundler/postit_trampoline"
 require "bundler/shared_helpers"
 
 if Bundler::SharedHelpers.in_bundle?
diff --git a/spec/other/trampoline_spec.rb b/spec/other/trampoline_spec.rb
index 2aac0a2c1d..9a8e0a4a5d 100644
--- a/spec/other/trampoline_spec.rb
+++ b/spec/other/trampoline_spec.rb
@@ -59,6 +59,24 @@ describe "bundler version trampolining" do
     end
   end
 
+  context "without BUNDLE_ENABLE_TRAMPOLINE" do
+    before { ENV["BUNDLE_ENABLE_TRAMPOLINE"] = nil }
+
+    context "when the version is >= 2" do
+      let(:version) { "2.7182818285" }
+      before do
+        simulate_bundler_version version do
+          install_gemfile! ""
+        end
+      end
+
+      it "trampolines automatically", :realworld => true do
+        bundle "--version"
+        expect(err).to include("Installing locked Bundler version #{version}...")
+      end
+    end
+  end
+
   context "installing missing bundler versions", :realworld => true do
     before do
       ENV["BUNDLER_VERSION"] = "1.12.3"