Add -git_revision flag to estimate command

Allows one to define the git revision of the specified Go package
to estimate, defaulting to the default behavior of go get.
Useful in case you do not want to estimate the latest version.

Author: n-peugnet

estimate.go

@@ -17,7 +17,7 @@ import (
 // majorVersionRegexp checks if an import path contains a major version suffix.
 var majorVersionRegexp = regexp.MustCompile(`([/.])v([0-9]+)$`)
 
-func get(gopath, repodir, repo string) error {
+func get(gopath, repodir, repo, rev string) error {
 	done := make(chan struct{})
 	defer close(done)
 	go progressSize("go get", repodir, done)
@@ -29,7 +29,11 @@ func get(gopath, repodir, repo string) error {
 	// to package into a single Debian package, and using “go get -t
 	// github.com/jacobsa/util” fails because there are no buildable go files
 	// in the top level of that repository.
-	cmd := exec.Command("go", "get", "-t", repo+"/...")
+	packages := repo + "/..."
+	if rev != "" {
+		packages += "@" + rev
+	}
+	cmd := exec.Command("go", "get", "-t", packages)
 	cmd.Dir = repodir
 	cmd.Stderr = os.Stderr
 	cmd.Env = append([]string{
@@ -76,7 +80,7 @@ func otherVersions(mod string) (mods []string) {
 	return
 }
 
-func estimate(importpath string) error {
+func estimate(importpath, revision string) error {
 	removeTemp := func(path string) {
 		if err := forceRemoveAll(path); err != nil {
 			log.Printf("could not remove all %s: %v", path, err)
@@ -102,7 +106,7 @@ func estimate(importpath string) error {
 		return fmt.Errorf("create dummymod: %w", err)
 	}
 
-	if err := get(gopath, repodir, importpath); err != nil {
+	if err := get(gopath, repodir, importpath, revision); err != nil {
 		return fmt.Errorf("go get: %w", err)
 	}
 
@@ -113,7 +117,7 @@ func estimate(importpath string) error {
 
 	if found {
 		// Fetch un-vendored dependencies
-		if err := get(gopath, repodir, importpath); err != nil {
+		if err := get(gopath, repodir, importpath, revision); err != nil {
 			return fmt.Errorf("fetch un-vendored: go get: %w", err)
 		}
 	}
@@ -246,8 +250,19 @@ func execEstimate(args []string) {
 		fmt.Fprintf(os.Stderr, "Estimates the work necessary to bring <go-module-importpath> into Debian\n"+
 			"by printing all currently unpacked repositories.\n")
 		fmt.Fprintf(os.Stderr, "Example: %s estimate github.com/Debian/dh-make-golang\n", os.Args[0])
+		fmt.Fprintf(os.Stderr, "\n")
+		fmt.Fprintf(os.Stderr, "Flags:\n")
+		fs.PrintDefaults()
 	}
 
+	var gitRevision string
+	fs.StringVar(&gitRevision,
+		"git_revision",
+		"",
+		"git revision (see gitrevisions(7)) of the specified Go package\n"+
+			"to estimate, defaulting to the default behavior of go get.\n"+
+			"Useful in case you do not want to estimate the latest version.")
+
 	err := fs.Parse(args)
 	if err != nil {
 		log.Fatalf("parse args: %s", err)
@@ -258,9 +273,9 @@ func execEstimate(args []string) {
 		os.Exit(1)
 	}
 
-	// TODO: support the -git_revision flag
+	gitRevision = strings.TrimSpace(gitRevision)
 
-	if err := estimate(fs.Arg(0)); err != nil {
+	if err := estimate(fs.Arg(0), gitRevision); err != nil {
 		log.Fatalf("estimate: %s", err)
 	}
 }