Add source timestamp result file for Git step tool

Extend Git step tool to write a result file container the source
timestamp of the commit that is checked out.

cmd/git/main.go

@@ -46,20 +46,21 @@ func (e ExitError) Error() string {
 }
 
 type settings struct {
-	help                   bool
-	url                    string
-	revision               string
-	depth                  uint
-	target                 string
-	resultFileCommitSha    string
-	resultFileCommitAuthor string
-	resultFileBranchName   string
-	secretPath             string
-	skipValidation         bool
-	gitURLRewrite          bool
-	resultFileErrorMessage string
-	resultFileErrorReason  string
-	verbose                bool
+	help                      bool
+	url                       string
+	revision                  string
+	depth                     uint
+	target                    string
+	resultFileCommitSha       string
+	resultFileCommitAuthor    string
+	resultFileBranchName      string
+	resultFileCommitTimestamp string
+	secretPath                string
+	skipValidation            bool
+	gitURLRewrite             bool
+	resultFileErrorMessage    string
+	resultFileErrorReason     string
+	verbose                   bool
 }
 
 var flagValues settings
@@ -81,6 +82,7 @@ func init() {
 	pflag.StringVar(&flagValues.target, "target", "", "The target directory of the clone operation")
 	pflag.StringVar(&flagValues.resultFileCommitSha, "result-file-commit-sha", "", "A file to write the commit sha to.")
 	pflag.StringVar(&flagValues.resultFileCommitAuthor, "result-file-commit-author", "", "A file to write the commit author to.")
+	pflag.StringVar(&flagValues.resultFileCommitTimestamp, "result-file-commit-timestamp", "", "A file to write the commit timestamp to.")
 	pflag.StringVar(&flagValues.resultFileBranchName, "result-file-branch-name", "", "A file to write the branch name to.")
 	pflag.StringVar(&flagValues.secretPath, "secret-path", "", "A directory that contains a secret. Either username and password for basic authentication. Or a SSH private key and optionally a known hosts file. Optional.")
 
@@ -180,6 +182,17 @@ func runGitClone(ctx context.Context) error {
 		}
 	}
 
+	if flagValues.resultFileCommitTimestamp != "" {
+		output, err := git(ctx, "-C", flagValues.target, "show", "--no-patch", "--format=%ct")
+		if err != nil {
+			return err
+		}
+
+		if err = os.WriteFile(flagValues.resultFileCommitTimestamp, []byte(output), 0644); err != nil {
+			return err
+		}
+	}
+
 	if strings.TrimSpace(flagValues.revision) == "" && strings.TrimSpace(flagValues.resultFileBranchName) != "" {
 		output, err := git(ctx, "-C", flagValues.target, "rev-parse", "--abbrev-ref", "HEAD")
 		if err != nil {

cmd/git/main_test.go

@@ -471,6 +471,21 @@ var _ = Describe("Git Resource", func() {
 				})
 			})
 		})
+
+		It("should store commit-timestamp into file specified in --result-file-commit-timestamp flag", func() {
+			withTempFile("commit-timestamp", func(filename string) {
+				withTempDir(func(target string) {
+					Expect(run(withArgs(
+						"--url", exampleRepo,
+						"--target", target,
+						"--revision", "v0.1.0",
+						"--result-file-commit-timestamp", filename,
+					))).ToNot(HaveOccurred())
+
+					Expect(filecontent(filename)).To(Equal("1619426578"))
+				})
+			})
+		})
 	})
 
 	Context("Some tests mutate or depend on git configurations. They must run sequentially to avoid race-conditions.", Ordered, func() {