Fix bundler 4.x incompatibility caused by rubygems 4.x update

Rubygems 4.0.9 ships bundler 4.x as a default gem. When UpdateRubygems()
runs 'ruby setup.rb', it installs bundler 4.0.9 which overwrites the
buildpack's bundler 2.x. Bundler 4.x changed 'bundle version' output
format (omits 'Bundler version' prefix), breaking GetBundlerVersion().

Changes:
- GetBundlerVersion() regex: handle both bundler 2.x and 4.x output formats
- UpdateRubygems(): re-install manifest bundler after 'ruby setup.rb'
- InstallBundler(): invert version selection to default to 2.x.x
- VendorBundlePath(): only bundler 1.x uses nested path (future-proof)
- InstallGems(): only bundler 1.x skips BUNDLED WITH removal (future-proof)
- Tests: add bundler 2.x/4.x test cases, update UpdateRubygems test

Author: tnikolova82

src/ruby/supply/supply.go

@@ -323,11 +323,11 @@ func (s *Supplier) InstallBundler() error {
 		matches = []string{"", "2"}
 	}
 
-	if strings.HasPrefix(matches[1], "2") {
-		return s.installBundler("2.x.x")
+	if strings.HasPrefix(matches[1], "1") {
+		return s.installBundler("1.x.x")
 	}
 
-	return s.installBundler("1.x.x")
+	return s.installBundler("2.x.x")
 }
 
 func (s *Supplier) InstallNode() error {
@@ -468,7 +468,7 @@ func (s *Supplier) VendorBundlePath() (string, error) {
 		return "", err
 	}
 
-	if strings.HasPrefix(bundlerVersion, "2.") {
+	if !strings.HasPrefix(bundlerVersion, "1.") {
 		return "vendor_bundle", nil
 	}
 
@@ -610,6 +610,15 @@ func (s *Supplier) UpdateRubygems() error {
 		return fmt.Errorf("Could not install rubygems: %v", err)
 	}
 
+	// Rubygems 4.x ships bundler 4.x as a default gem. Running setup.rb
+	// overwrites the buildpack-installed bundler (2.x) with bundler 4.x,
+	// which has incompatible output format changes and untested behavior.
+	// Re-install the buildpack's bundler to restore the manifest version.
+	s.Log.Debug("Re-installing bundler after rubygems update")
+	if err := s.InstallBundler(); err != nil {
+		return fmt.Errorf("Could not re-install bundler after rubygems update: %v", err)
+	}
+
 	return nil
 }
 
@@ -739,7 +748,7 @@ func (s *Supplier) InstallGems() error {
 			return fmt.Errorf("could not read Bundled With version from gemfile.lock: %s", err)
 		}
 
-		if bundledWithVersion != bundlerVersion && strings.HasPrefix(bundledWithVersion, "2") {
+		if bundledWithVersion != bundlerVersion && !strings.HasPrefix(bundledWithVersion, "1") {
 			if err := s.removeIncompatibleBundledWithVersion(bundledWithVersion); err != nil {
 				return fmt.Errorf("could not remove Bundled With from end of "+
 					"gemfile.lock: %s", err)

src/ruby/supply/supply_test.go

@@ -68,7 +68,7 @@ var _ = Describe("Supply", func() {
 		mockCtrl = gomock.NewController(GinkgoT())
 
 		mockManifest = NewMockManifest(mockCtrl)
-		mockManifest.EXPECT().AllDependencyVersions("bundler").Return([]string{"1.17.2"}).AnyTimes()
+		mockManifest.EXPECT().AllDependencyVersions("bundler").Return([]string{"1.17.2", "2.7.2"}).AnyTimes()
 
 		mockInstaller = NewMockInstaller(mockCtrl)
 
@@ -133,6 +133,28 @@ var _ = Describe("Supply", func() {
 		})
 	})
 
+	Describe("InstallBundler with bundler 2.x BUNDLED WITH", func() {
+
+		var tempSupplier supply.Supplier
+
+		BeforeEach(func() {
+			tempSupplier = *supplier
+			mockStager := NewMockStager(mockCtrl)
+			tempSupplier.Stager = mockStager
+
+			mockInstaller.EXPECT().InstallDependency(libbuildpack.Dependency{Name: "bundler", Version: "2.7.2"}, gomock.Any())
+			mockStager.EXPECT().LinkDirectoryInDepDir(gomock.Any(), gomock.Any())
+			mockStager.EXPECT().DepDir().AnyTimes()
+
+			err := os.WriteFile(filepath.Join(buildDir, "Gemfile.lock"), []byte("BUNDLED WITH\n    2.4.0"), 0644)
+			Expect(err).NotTo(HaveOccurred())
+		})
+
+		It("installs bundler 2.x matching constraint given", func() {
+			Expect(tempSupplier.InstallBundler()).To(Succeed())
+		})
+	})
+
 	Describe("InstallNode", func() {
 		var tempSupplier supply.Supplier
 
@@ -389,6 +411,23 @@ var _ = Describe("Supply", func() {
 				Expect(actualEnv).To(Equal(expectedEnv))
 			})
 		})
+
+		Describe("With Bundler version 4.x.x (future-proofing)", func() {
+			BeforeEach(func() {
+				mockVersions.EXPECT().GetBundlerVersion().Return("4.0.9", nil).AnyTimes()
+
+				mockStager.EXPECT().DepDir().Return("some/test-dir").AnyTimes()
+				mockStager.EXPECT().WriteEnvFile(gomock.Any(), gomock.Any()).Return(nil)
+			})
+
+			It("should use vendor_bundle path like bundler 2.x", func() {
+				Expect(tempSupplier.AddPostRubyGemsInstallDefaultEnv()).To(Succeed())
+
+				expectedEnv := "some/test-dir/vendor_bundle"
+				actualEnv := os.Getenv("BUNDLE_PATH")
+				Expect(actualEnv).To(Equal(expectedEnv))
+			})
+		})
 	})
 
 	Describe("CopyDirToTemp", func() {
@@ -1145,6 +1184,16 @@ var _ = Describe("Supply", func() {
 				})
 				mockCommand.EXPECT().Output(gomock.Any(), "ruby", "setup.rb")
 
+				// After ruby setup.rb, UpdateRubygems re-installs bundler.
+				// InstallBundler reads Gemfile.lock (not present here, so defaults
+				// to 2.x.x constraint) and installs bundler from the manifest.
+				mockInstaller.EXPECT().InstallDependency(gomock.Any(), gomock.Any()).Do(func(dep libbuildpack.Dependency, installDir string) {
+					Expect(dep.Name).To(Equal("bundler"))
+					Expect(dep.Version).To(Equal("2.7.2"))
+					// Create bin dir so LinkDirectoryInDepDir succeeds
+					Expect(os.MkdirAll(filepath.Join(installDir, "bin"), 0755)).To(Succeed())
+				})
+
 				Expect(supplier.UpdateRubygems()).To(Succeed())
 			})
 

src/ruby/versions/ruby.go

@@ -59,7 +59,9 @@ func (v *Versions) GetBundlerVersion() (string, error) {
 		return "", err
 	}
 
-	re := regexp.MustCompile(`Bundler version (\d+\.\d+\.\d+) .*`)
+	// Bundler 2.x outputs "Bundler version X.Y.Z (...)" but bundler 4.x
+	// omits the "Bundler version" prefix and outputs just "X.Y.Z (...)".
+	re := regexp.MustCompile(`(?:Bundler version )?(\d+\.\d+\.\d+)`)
 	match := re.FindStringSubmatch(stdout.String())
 
 	if len(match) != 2 {
@@ -192,9 +194,11 @@ func (v *Versions) GemMajorVersion(gem string) (int, error) {
 	}
 }
 
-//Should return true if either:
+// Should return true if either:
 // (1) the only platform in the Gemfile.lock is windows (mingw/mswin)
-//     -or-
+//
+//	-or-
+//
 // (2) the Gemfile.lock line endings are /r/n, rather than just /n
 func (v *Versions) HasWindowsGemfileLock() (bool, error) {
 	gemfileLockPath := v.Gemfile() + ".lock"