commands/track: teach track how to --dry-run

commands/command_track.go

@@ -28,6 +28,7 @@ var (
 
 	trackNoTouchFlag        bool
 	trackVerboseLoggingFlag bool
+	trackDryRunFlag         bool
 )
 
 func trackCommand(cmd *cobra.Command, args []string) {
@@ -109,21 +110,23 @@ ArgsLoop:
 			continue
 		}
 
+		if !trackDryRunFlag {
 			encodedArg := strings.Replace(pattern, " ", "[[:space:]]", -1)
-		_, err = attributesFile.WriteString(fmt.Sprintf("%s filter=lfs diff=lfs merge=lfs -text\n", encodedArg))
+			_, err := attributesFile.WriteString(fmt.Sprintf("%s filter=lfs diff=lfs merge=lfs -text\n", encodedArg))
 			if err != nil {
 				Print("Error adding path %s", pattern)
 				continue
 			}
+		}
 		Print("Tracking %s", pattern)
 
-		if !trackNoTouchFlag {
+		if !trackNoTouchFlag || trackDryRunFlag {
-			now := time.Now()
 			for _, f := range gittracked {
-				if trackVerboseLoggingFlag {
+				if trackVerboseLoggingFlag || trackDryRunFlag {
 					Print("Git LFS: touching %s", f)
 				}
 
+				if !trackDryRunFlag {
 					err := os.Chtimes(f, now, now)
 					if err != nil {
 						LoggedError(err, "Error marking %q modified", f)
@@ -133,6 +136,7 @@ ArgsLoop:
 			}
 		}
 	}
+}
 
 type mediaPath struct {
 	Path   string
@@ -229,6 +233,7 @@ func blocklistItem(name string) string {
 func init() {
 	trackCmd.Flags().BoolVarP(&trackNoTouchFlag, "no-touch", "n", false, "skip modifying files matched by the glob")
 	trackCmd.Flags().BoolVarP(&trackVerboseLoggingFlag, "verbose", "v", false, "log which files are being tracked and modified")
+	trackCmd.Flags().BoolVarP(&trackDryRunFlag, "dry-run", "d", false, "preview results of running `git lfs track`")
 
 	RootCmd.AddCommand(trackCmd)
 }

docs/man/git-lfs-track.1.ronn

@@ -21,6 +21,17 @@ the currently-tracked paths.
   If enabled, have `git lfs track` log files which it will touch. Disabled by
   default.
 
+* `--dry-run` `d`:
+  If enabled, have `git lfs track` log all actions it would normally take
+  (adding entries to .gitattributes, touching files on disk, etc) without
+  preforming any mutative operations to the disk.
+
+  `git lfs track --dry-run [files]` is equivalent to calling
+  `git lfs track --no-touch --verbose` and reverting any changes made to
+  .gitattributes.
+
+  Disabled by default.
+
 ## EXAMPLES
 
 * List the paths that Git LFS is currently tracking:

test/test-track.sh

@@ -80,6 +80,27 @@ begin_test "track --verbose"
 )
 end_test
 
+begin_test "track --dry-run"
+(
+  set -e
+
+  reponame="track_dry_run"
+  mkdir "$reponame"
+  cd "$reponame"
+  git init
+
+  touch foo.dat
+  git add foo.dat
+
+  git lfs track --dry-run "foo.dat" 2>&1 > track.log
+  grep "Tracking foo.dat" track.log
+  grep "Git LFS: touching foo.dat" track.log
+
+  git status --porcelain 2>&1 > status.log
+  grep "A  foo.dat" status.log
+)
+end_test
+
 begin_test "track directory"
 (
   set -e