Fix bundler 2.7.2 binstub generation - copy instead of generate

Bundler 2.7+ refuses to create its own binstub, displaying:
'Bundler itself does not use binstubs because its version is selected by RubyGems'

Solution: Copy bundler's existing bundle executable from bundler/bin/bundle
to binstubs/bundle instead of trying to regenerate it with 'bundle binstubs bundler'.

Updated tests to mock bundler/bin/bundle file creation instead of mocking
the 'bundle binstubs' command execution.

Author: ramonskie

src/ruby/supply/supply.go

@@ -854,16 +854,24 @@ func (s *Supplier) regenerateBundlerBinStub(appDir string) error {
 		return fmt.Errorf("could not create binstubs directory: %v", err)
 	}
 
-	// Note: --path flag is deprecated in bundler 2.7+
-	// The bin path is already configured via 'bundle config set bin'
-	cmd := exec.Command("bundle", "binstubs", "bundler", "--force")
-	cmd.Dir = appDir
-	cmd.Stdout = text.NewIndentWriter(os.Stdout, []byte("       "))
-	cmd.Stderr = text.NewIndentWriter(os.Stderr, []byte("       "))
-	if err := s.Command.Run(cmd); err != nil {
-		return err
+	// Note: Bundler 2.7+ refuses to create its own binstub with message:
+	// "Bundler itself does not use binstubs because its version is selected by RubyGems"
+	// Instead, we copy the bundle executable from bundler/bin to binstubs directory
+	bundlerBin := filepath.Join(s.Stager.DepDir(), "bundler", "bin", "bundle")
+	binstubBundle := filepath.Join(s.Stager.DepDir(), "binstubs", "bundle")
+
+	if exists, err := libbuildpack.FileExists(bundlerBin); err != nil {
+		return fmt.Errorf("could not check if bundler bin exists: %v", err)
+	} else if exists {
+		// Copy bundler's bundle executable to binstubs
+		if err := libbuildpack.CopyFile(bundlerBin, binstubBundle); err != nil {
+			return fmt.Errorf("could not copy bundle binstub: %v", err)
+		}
+	} else {
+		return fmt.Errorf("bundler bin not found at %s", bundlerBin)
 	}
-	return libbuildpack.CopyFile(filepath.Join(s.Stager.DepDir(), "binstubs", "bundle"), filepath.Join(s.Stager.DepDir(), "bin", "bundle"))
+
+	return libbuildpack.CopyFile(binstubBundle, filepath.Join(s.Stager.DepDir(), "bin", "bundle"))
 }
 
 func (s *Supplier) EnableLDLibraryPathEnv() error {

src/ruby/supply/supply_test.go

@@ -8,8 +8,6 @@ import (
 	"os/exec"
 	"path/filepath"
 
-	"reflect"
-
 	"github.com/cloudfoundry/ruby-buildpack/src/ruby/cache"
 	"github.com/cloudfoundry/ruby-buildpack/src/ruby/supply"
 
@@ -481,17 +479,16 @@ var _ = Describe("Supply", func() {
 
 		const windowsWarning = "**WARNING** Windows line endings detected in Gemfile. Your app may fail to stage. Please use UNIX line endings."
 
-		handleBundleBinstubRegeneration := func(cmd *exec.Cmd) error {
-			if len(cmd.Args) >= 4 && reflect.DeepEqual(cmd.Args[0:4], []string{"bundle", "binstubs", "bundler", "--force"}) {
-				binstubsPath := filepath.Join(depsDir, depsIdx, "binstubs")
-				Expect(os.MkdirAll(binstubsPath, 0755)).To(Succeed())
-				Expect(os.WriteFile(filepath.Join(binstubsPath, "bundle"), []byte("new bundle binstub"), 0644)).To(Succeed())
-			}
-			return nil
+		// Setup bundler bin directory with bundle executable (simulates bundler installation)
+		setupBundlerBin := func() {
+			bundlerBinDir := filepath.Join(depsDir, depsIdx, "bundler", "bin")
+			Expect(os.MkdirAll(bundlerBinDir, 0755)).To(Succeed())
+			Expect(os.WriteFile(filepath.Join(bundlerBinDir, "bundle"), []byte("new bundle binstub"), 0755)).To(Succeed())
 		}
 
 		itRegeneratesBundleBinstub := func() {
 			It("Re-generates the bundler binstub to replace older, rails-generated ones that are incompatible with bundler > 1.16.0", func() {
+				setupBundlerBin()
 				Expect(supplier.InstallGems()).To(Succeed())
 				Expect(os.ReadFile(filepath.Join(depsDir, depsIdx, "binstubs", "bundle"))).To(Equal([]byte("new bundle binstub")))
 				Expect(os.ReadFile(filepath.Join(depsDir, depsIdx, "bin", "bundle"))).To(Equal([]byte("new bundle binstub")))
@@ -501,13 +498,14 @@ var _ = Describe("Supply", func() {
 		Context("Windows Gemfile", func() {
 			BeforeEach(func() {
 				mockVersions.EXPECT().HasWindowsGemfileLock().Return(false, nil)
-				mockCommand.EXPECT().Run(gomock.Any()).AnyTimes().Do(handleBundleBinstubRegeneration)
+				mockCommand.EXPECT().Run(gomock.Any()).AnyTimes()
 				Expect(os.WriteFile(filepath.Join(buildDir, "Gemfile"), []byte("source \"https://rubygems.org\"\r\ngem \"rack\"\r\n"), 0644)).To(Succeed())
 			})
 
 			itRegeneratesBundleBinstub()
 
 			It("Warns the user", func() {
+				setupBundlerBin()
 				Expect(supplier.InstallGems()).To(Succeed())
 				Expect(buffer.String()).To(ContainSubstring(windowsWarning))
 			})
@@ -521,10 +519,7 @@ var _ = Describe("Supply", func() {
 					if len(cmd.Args) > 2 && cmd.Args[1] == "install" {
 						Expect(os.MkdirAll(filepath.Join(cmd.Dir, ".bundle"), 0755)).To(Succeed())
 						Expect(os.WriteFile(filepath.Join(cmd.Dir, ".bundle", "config"), []byte("new bundle config"), 0644)).To(Succeed())
-					} else {
-						return handleBundleBinstubRegeneration(cmd)
 					}
-
 					return nil
 				})
 				Expect(os.WriteFile(filepath.Join(buildDir, "Gemfile"), []byte("source \"https://rubygems.org\"\ngem \"rack\"\n"), 0644)).To(Succeed())
@@ -537,11 +532,13 @@ var _ = Describe("Supply", func() {
 			itRegeneratesBundleBinstub()
 
 			It("Does not warn the user", func() {
+				setupBundlerBin()
 				Expect(supplier.InstallGems()).To(Succeed())
 				Expect(buffer.String()).ToNot(ContainSubstring(windowsWarning))
 			})
 
 			It("does not change .bundle/config", func() {
+				setupBundlerBin()
 				Expect(os.MkdirAll(filepath.Join(buildDir, ".bundle"), 0755)).To(Succeed())
 				Expect(os.WriteFile(filepath.Join(buildDir, ".bundle", "config"), []byte("orig content"), 0644)).To(Succeed())
 				Expect(os.ReadFile(filepath.Join(buildDir, ".bundle", "config"))).To(Equal([]byte("orig content")))
@@ -572,10 +569,9 @@ var _ = Describe("Supply", func() {
 						if cmd.Args[1] == "install" {
 							Expect(filepath.Join(cmd.Dir, "Gemfile")).To(BeAnExistingFile())
 							Expect(filepath.Join(cmd.Dir, "Gemfile.lock")).To(BeAnExistingFile())
-						} else {
-							handleBundleBinstubRegeneration(cmd)
 						}
 					})
+					setupBundlerBin()
 					Expect(supplier.InstallGems()).To(Succeed())
 
 					Expect(os.ReadFile(filepath.Join(buildDir, "Gemfile.lock"))).To(ContainSubstring(gemfileLock))
@@ -588,10 +584,9 @@ var _ = Describe("Supply", func() {
 						if cmd.Args[1] == "install" {
 							Expect(cmd.Dir).ToNot(Equal(buildDir))
 							installCalled = true
-						} else {
-							handleBundleBinstubRegeneration(cmd)
 						}
 					})
+					setupBundlerBin()
 					Expect(supplier.InstallGems()).To(Succeed())
 					Expect(installCalled).To(BeTrue())
 				})
@@ -614,10 +609,9 @@ var _ = Describe("Supply", func() {
 							Expect(filepath.Join(cmd.Dir, "Gemfile")).To(BeAnExistingFile())
 							Expect(filepath.Join(cmd.Dir, "Gemfile.lock")).ToNot(BeAnExistingFile())
 							Expect(os.WriteFile(filepath.Join(cmd.Dir, "Gemfile.lock"), []byte(newGemfileLock), 0644)).To(Succeed())
-						} else {
-							handleBundleBinstubRegeneration(cmd)
 						}
 					})
+					setupBundlerBin()
 					Expect(supplier.InstallGems()).To(Succeed())
 
 					Expect(os.ReadFile(filepath.Join(buildDir, "Gemfile.lock"))).To(ContainSubstring(gemfileLock))
@@ -630,10 +624,9 @@ var _ = Describe("Supply", func() {
 						if cmd.Args[1] == "install" {
 							Expect(cmd.Dir).ToNot(Equal(buildDir))
 							installCalled = true
-						} else {
-							handleBundleBinstubRegeneration(cmd)
 						}
 					})
+					setupBundlerBin()
 					Expect(supplier.InstallGems()).To(Succeed())
 					Expect(installCalled).To(BeTrue())
 				})