Loosens bundler version requirement to matching major

Bundler only enforces that version used to `bundle install` match the
major version specified in the `Gemfile.lock`. We now parse the version
specified in the `Gemfile.lock` and request any version of bundler that
matches that major version.

gemfile_lock_parser.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"os"
 	"strings"
+
+	"github.com/Masterminds/semver"
 )
 
 type GemfileLockParser struct{}
@@ -27,7 +29,12 @@ func (p GemfileLockParser) ParseVersion(path string) (string, error) {
 	for scanner.Scan() {
 		if strings.TrimSpace(scanner.Text()) == "BUNDLED WITH" {
 			if scanner.Scan() {
-				return strings.TrimSpace(scanner.Text()), nil
+				version, err := semver.NewVersion(strings.TrimSpace(scanner.Text()))
+				if err != nil {
+					return "", fmt.Errorf("failed to parse Gemfile.lock: %w", err)
+				}
+
+				return fmt.Sprintf("%d.*.*", version.Major()), nil
 			}
 		}
 	}

gemfile_lock_parser_test.go

@@ -50,10 +50,10 @@ BUNDLED WITH
 	})
 
 	context("ParseVersion", func() {
-		it("parses the bundler version from a Gemfile.lock file", func() {
+		it("parses the bundler major version from a Gemfile.lock file", func() {
 			version, err := parser.ParseVersion(path)
 			Expect(err).NotTo(HaveOccurred())
-			Expect(version).To(Equal("1.2.3"))
+			Expect(version).To(Equal("1.*.*"))
 		})
 
 		context("when the Gemfile.lock file does not exist", func() {
@@ -80,6 +80,32 @@ BUNDLED WITH
 					Expect(err).To(MatchError(ContainSubstring("permission denied")))
 				})
 			})
+
+			context("when the bundler version is not valid semver", func() {
+				it.Before(func() {
+					err := ioutil.WriteFile(path, []byte(`GEM
+  remote: https://rubygems.org/
+  specs:
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+
+RUBY VERSION
+   ruby 2.6.3p62
+
+BUNDLED WITH
+	 not semver`), 0600)
+					Expect(err).NotTo(HaveOccurred())
+				})
+
+				it("returns an error", func() {
+					_, err := parser.ParseVersion(path)
+					Expect(err).To(MatchError(ContainSubstring("failed to parse Gemfile.lock:")))
+					Expect(err).To(MatchError(ContainSubstring("Invalid Semantic Version")))
+				})
+			})
 		})
 	})
 }

go.mod

@@ -2,6 +2,7 @@ module github.com/paketo-buildpacks/bundler
 
 require (
 	github.com/BurntSushi/toml v0.3.1
+	github.com/Masterminds/semver v1.5.0
 	github.com/onsi/gomega v1.10.4
 	github.com/paketo-buildpacks/occam v0.0.23
 	github.com/paketo-buildpacks/packit v0.6.0
@@ -10,4 +11,4 @@ require (
 	gopkg.in/yaml.v2 v2.4.0
 )
 
-go 1.13
+go 1.15

integration/gemfile_lock_test.go

@@ -92,7 +92,7 @@ func testGemfileLock(t *testing.T, context spec.G, it spec.S) {
 				MatchRegexp(fmt.Sprintf(`%s \d+\.\d+\.\d+`, settings.Buildpack.Name)),
 				"  Resolving Bundler version",
 				"    Candidate version sources (in priority order):",
-				MatchRegexp(`      Gemfile.lock -> \"1\.17\.\d+\"`),
+				"      Gemfile.lock -> \"1.*.*\"",
 				"      <unknown>    -> \"*\"",
 				"",
 				MatchRegexp(`    Selected Bundler version \(using Gemfile\.lock\): 1\.17\.\d+`),

integration/reuse_layer_rebuild_test.go

@@ -201,7 +201,7 @@ func testReusingLayerRebuild(t *testing.T, context spec.G, it spec.S) {
 				MatchRegexp(fmt.Sprintf(`%s \d+\.\d+\.\d+`, settings.Buildpack.Name)),
 				"  Resolving Bundler version",
 				"    Candidate version sources (in priority order):",
-				MatchRegexp(`    Gemfile.lock -> \"1\.17\.\d+\"`),
+				"      Gemfile.lock -> \"1.*.*\"",
 				"      <unknown>    -> \"*\"",
 				"",
 				MatchRegexp(`    Selected Bundler version \(using Gemfile\.lock\): 1\.17\.\d+`),
@@ -230,7 +230,7 @@ func testReusingLayerRebuild(t *testing.T, context spec.G, it spec.S) {
 			Expect(err).NotTo(HaveOccurred())
 
 			re := regexp.MustCompile(`BUNDLED WITH\s+\d+\.\d+\.\d+`)
-			err = ioutil.WriteFile(filepath.Join(source, "Gemfile.lock"), re.ReplaceAll(contents, []byte("BUNDLED WITH\n   2.*")), 0644)
+			err = ioutil.WriteFile(filepath.Join(source, "Gemfile.lock"), re.ReplaceAll(contents, []byte("BUNDLED WITH\n   2.1.4")), 0644)
 			Expect(err).NotTo(HaveOccurred())
 
 			// Second pack build
@@ -247,7 +247,7 @@ func testReusingLayerRebuild(t *testing.T, context spec.G, it spec.S) {
 				MatchRegexp(fmt.Sprintf(`%s \d+\.\d+\.\d+`, settings.Buildpack.Name)),
 				"  Resolving Bundler version",
 				"    Candidate version sources (in priority order):",
-				"      Gemfile.lock -> \"2.*\"",
+				"      Gemfile.lock -> \"2.*.*\"",
 				"      <unknown>    -> \"*\"",
 				"",
 				MatchRegexp(`    Selected Bundler version \(using Gemfile\.lock\): 2\.\d+\.\d+`),

integration/testdata/gemfile_lock_version/Gemfile.lock

@@ -11,4 +11,4 @@ RUBY VERSION
    ruby 2.6.3p62
 
 BUNDLED WITH
-   1.17.3
+   1.15.2