commands: warn if working copy is dirty

In 'git lfs migrate import' and 'git lfs migrate export', Git LFS makes
destructive changes to a caller's repository and therefore invokes 'git
checkout --force', which throws away local changes.

To prevent this, let's introduce a check that notifies users when they
are going to throw away local changes, and allows for the user to abort
if they do not wish to discard their local changes.

With this, a user can safely migrate over dirty repositories (i.e., in
the case that they wanted to fix a file that should have been in Git
LFS, but wasn't) without having to finagle their repository to get it
into a migrate-able state.

For users with lots of pending migrations, also teach --yes, which
allows a user to avoid the check, and instead simply prints the warning
message to STDERR.

commands/command_migrate.go

@@ -1,7 +1,9 @@
 package commands
 
 import (
+	"bufio"
 	"fmt"
+	"io"
 	"path/filepath"
 	"strings"
 
@@ -21,6 +23,10 @@ var (
 	// in the migration.
 	migrateExcludeRefs []string
 
+	// migrateYes indicates that an answer of 'yes' should be presumed
+	// whenever 'git lfs migrate' asks for user input.
+	migrateYes bool
+
 	// migrateSkipFetch assumes that the client has the latest copy of
 	// remote references, and thus should not contact the remote for a set
 	// of updated references.
@@ -294,6 +300,50 @@ func getHistoryRewriter(cmd *cobra.Command, db *gitobj.ObjectDatabase, l *tasklo
 		githistory.WithFilter(filter), githistory.WithLogger(l))
 }
 
+func ensureWorkingCopyClean(in io.Reader, out io.Writer) {
+	dirty, err := git.IsWorkingCopyDirty()
+	if err != nil {
+		ExitWithError(errors.Wrap(err,
+			"fatal: could not determine if working copy is dirty"))
+	}
+
+	if !dirty {
+		return
+	}
+
+	var proceed bool
+	if migrateYes {
+		proceed = true
+	} else {
+		answer := bufio.NewReader(in)
+	L:
+		for {
+			fmt.Fprintf(out, "migrate: override changes in your working copy? [Y/n] ")
+			s, _, err := answer.ReadLine()
+			if err != nil {
+				ExitWithError(errors.Wrap(err,
+					"fatal: could not read answer"))
+			}
+
+			switch strings.TrimSpace(string(s)) {
+			case "n", "N":
+				proceed = false
+				break L
+			case "y", "Y":
+				proceed = true
+				break L
+			}
+			fmt.Fprintf(out, "\n")
+		}
+	}
+
+	if proceed {
+		fmt.Fprintf(out, "migrate: changes in your working copy will be overridden ...\n")
+	} else {
+		Exit("migrate: working copy must not be dirty")
+	}
+}
+
 func init() {
 	info := NewCommand("info", migrateInfoCommand)
 	info.Flags().IntVar(&migrateInfoTopN, "top", 5, "--top=<n>")
@@ -321,6 +371,8 @@ func init() {
 		cmd.PersistentFlags().BoolVar(&migrateEverything, "everything", false, "Migrate all local references")
 		cmd.PersistentFlags().BoolVar(&migrateSkipFetch, "skip-fetch", false, "Assume up-to-date remote references.")
 
+		cmd.PersistentFlags().BoolVarP(&migrateYes, "yes", "y", false, "Don't prompt for answers.")
+
 		cmd.AddCommand(exportCmd, importCmd, info)
 	})
 }

commands/command_migrate_export.go

@@ -17,6 +17,8 @@ import (
 )
 
 func migrateExportCommand(cmd *cobra.Command, args []string) {
+	ensureWorkingCopyClean(os.Stdin, os.Stderr)
+
 	l := tasklog.NewLogger(os.Stderr)
 	defer l.Close()
 

commands/command_migrate_import.go

@@ -22,6 +22,8 @@ import (
 )
 
 func migrateImportCommand(cmd *cobra.Command, args []string) {
+	ensureWorkingCopyClean(os.Stdin, os.Stderr)
+
 	l := tasklog.NewLogger(os.Stderr)
 	defer l.Close()
 

git/git.go

@@ -1192,3 +1192,21 @@ func IsFileModified(filepath string) (bool, error) {
 
 	return matched, nil
 }
+
+// IsWorkingCopyDirty returns true if and only if the working copy in which the
+// command was executed is dirty as compared to the index.
+//
+// If the status of the working copy could not be determined, an error will be
+// returned instead.
+func IsWorkingCopyDirty() (bool, error) {
+	bare, err := IsBare()
+	if bare || err != nil {
+		return false, err
+	}
+
+	out, err := gitSimple("status", "--porcelain")
+	if err != nil {
+		return false, err
+	}
+	return len(out) != 0, nil
+}

test/test-migrate-export.sh

@@ -132,7 +132,7 @@ begin_test "migrate export (bare repository)"
 
   md_oid="$(calc_oid "$(cat a.md)")"
   txt_oid="$(calc_oid "$(cat a.txt)")"
-  
+
   make_bare
 
   assert_pointer "refs/heads/master" "a.txt" "$txt_oid" "30"
@@ -198,7 +198,7 @@ begin_test "migrate export (no filter)"
 
   setup_multiple_local_branches_tracked
 
-  git lfs migrate export 2>&1 | tee migrate.log
+  git lfs migrate export --yes 2>&1 | tee migrate.log
   if [ ${PIPESTATUS[0]} -eq 0 ]; then
     echo >&2 "fatal: expected git lfs migrate export to fail, didn't"
     exit 1
@@ -330,7 +330,7 @@ begin_test "migrate export (include/exclude ref)"
     --include="*.txt" \
     --include-ref=refs/heads/my-feature \
     --exclude-ref=refs/heads/master
-  
+
   assert_pointer "refs/heads/master" "a.md" "$md_master_oid" "21"
   assert_pointer "refs/heads/master" "a.txt" "$txt_master_oid" "20"
 
@@ -432,7 +432,8 @@ begin_test "migrate export (invalid --remote)"
 
   setup_single_remote_branch_tracked
 
-  git lfs migrate export --include="*" --remote="zz" 2>&1 | tee migrate.log
+  git lfs migrate export --include="*" --remote="zz" --yes 2>&1 \
+    | tee migrate.log
   if [ ${PIPESTATUS[0]} -eq 0 ]; then
     echo >&2 "fatal: expected git lfs migrate export to fail, didn't"
     exit 1

test/test-migrate-fixtures.sh

@@ -553,6 +553,28 @@ setup_local_branch_with_symlink() {
   git commit -m "add symlink"
 }
 
+# setup_local_branch_with_dirty_copy creates a repository as follows:
+#
+#   A
+#    \
+#     refs/heads/master
+#
+# - Commit 'A' has the contents "a.txt\n" in a.txt, and marks a.txt as unclean
+#   in the working copy.
+setup_local_branch_with_dirty_copy() {
+  set -e
+
+  reponame="migrate-single-local-branch-with-dirty-copy"
+  remove_and_create_local_repo "$reponame"
+
+  echo "a.txt" > a.txt
+
+  git add a.txt
+  git commit -m "initial commit"
+
+  echo "2" >> a.txt
+}
+
 # make_bare converts the existing full checkout of a repository into a bare one,
 # and then `cd`'s into it.
 make_bare() {
@@ -587,4 +609,6 @@ remove_and_create_remote_repo() {
 
   setup_remote_repo "$reponame"
   clone_repo "$reponame" "$reponame"
+
+  rm clone.log
 }

test/test-migrate-fixup.sh

@@ -11,7 +11,7 @@ begin_test "migrate import (--fixup)"
 
   txt_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
 
-  git lfs migrate import --everything --fixup
+  git lfs migrate import --everything --fixup --yes
 
   assert_pointer "refs/heads/master" "a.txt" "$txt_oid" "120"
   assert_local_object "$txt_oid" "120"
@@ -31,7 +31,7 @@ begin_test "migrate import (--fixup, complex nested)"
   a_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
   b_oid="$(calc_oid "$(git cat-file -p :dir/b.txt)")"
 
-  git lfs migrate import --everything --fixup
+  git lfs migrate import --everything --fixup --yes
 
   assert_pointer "refs/heads/master" "a.txt" "$a_oid" "1"
   refute_pointer "refs/heads/master" "b.txt"
@@ -53,7 +53,7 @@ begin_test "migrate import (--fixup, --include)"
 
   setup_single_local_branch_tracked_corrupt
 
-  git lfs migrate import --everything --fixup --include="*.txt" 2>&1 \
+  git lfs migrate import --everything --fixup --yes --include="*.txt" 2>&1 \
     | tee migrate.log
 
   if [ "${PIPESTATUS[0]}" -eq 0 ]; then
@@ -71,7 +71,7 @@ begin_test "migrate import (--fixup, --exclude)"
 
   setup_single_local_branch_tracked_corrupt
 
-  git lfs migrate import --everything --fixup --exclude="*.txt" 2>&1 \
+  git lfs migrate import --everything --fixup --yes --exclude="*.txt" 2>&1 \
     | tee migrate.log
 
   if [ "${PIPESTATUS[0]}" -eq 0 ]; then
@@ -89,7 +89,7 @@ begin_test "migrate import (--fixup, --no-rewrite)"
 
   setup_single_local_branch_tracked_corrupt
 
-  git lfs migrate import --everything --fixup --no-rewrite 2>&1 \
+  git lfs migrate import --everything --fixup --yes --no-rewrite 2>&1 \
     | tee migrate.log
 
   if [ "${PIPESTATUS[0]}" -eq 0 ]; then

test/test-migrate-import-no-rewrite.sh

@@ -12,7 +12,7 @@ begin_test "migrate import --no-rewrite (default branch)"
   txt_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
   prev_commit_oid="$(git rev-parse HEAD)"
 
-  git lfs migrate import --no-rewrite *.txt
+  git lfs migrate import --no-rewrite --yes *.txt
 
   # Ensure our desired files were imported into git-lfs
   assert_pointer "refs/heads/master" "a.txt" "$txt_oid" "120"
@@ -46,7 +46,7 @@ begin_test "migrate import --no-rewrite (bare repository)"
   txt_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
   md_oid="$(calc_oid "$(git cat-file -p :a.md)")"
 
-  git lfs migrate import --no-rewrite a.txt a.md
+  git lfs migrate import --no-rewrite --yes a.txt a.md
 
   # Ensure our desired files were imported
   assert_pointer "refs/heads/master" "a.txt" "$txt_oid" "30"
@@ -78,7 +78,7 @@ begin_test "migrate import --no-rewrite (multiple branches)"
   txt_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
   md_feature_oid="$(calc_oid "$(git cat-file -p my-feature:a.md)")"
 
-  git lfs migrate import --no-rewrite *.txt *.md
+  git lfs migrate import --no-rewrite --yes *.txt *.md
 
   # Ensure our desired files were imported
   assert_pointer "refs/heads/master" "a.md" "$md_oid" "140"
@@ -111,7 +111,7 @@ begin_test "migrate import --no-rewrite (no .gitattributes)"
   setup_multiple_local_branches
 
   # Ensure command fails if no .gitattributes files are present
-  git lfs migrate import --no-rewrite *.txt *.md 2>&1 | tee migrate.log
+  git lfs migrate import --no-rewrite --yes *.txt *.md 2>&1 | tee migrate.log
   if [ ${PIPESTATUS[0]} -eq 0 ]; then
     echo >&2 "fatal: expected git lfs migrate import --no-rewrite to fail, didn't"
     exit 1
@@ -139,7 +139,7 @@ begin_test "migrate import --no-rewrite (nested .gitattributes)"
   nested_md_oid="$(calc_oid "$(git cat-file -p :b/a.md)")"
   txt_oid="$(calc_oid "$(git cat-file -p :a.txt)")"
 
-  git lfs migrate import --no-rewrite a.txt b/a.md
+  git lfs migrate import --no-rewrite --yes a.txt b/a.md
 
   # Ensure a.txt and subtree/a.md were imported, even though *.md only exists in the
   # nested subtree/.gitattributes file
@@ -152,7 +152,7 @@ begin_test "migrate import --no-rewrite (nested .gitattributes)"
 
   # Failure should occur when trying to import a.md as no entry exists in
   # top-level .gitattributes file
-  git lfs migrate import --no-rewrite a.md 2>&1 | tee migrate.log
+  git lfs migrate import --no-rewrite --yes a.md 2>&1 | tee migrate.log
   if [ ${PIPESTATUS[0]} -eq 0 ]; then
     echo >&2 "fatal: expected git lfs migrate import --no-rewrite to fail, didn't"
     exit 1
@@ -171,7 +171,7 @@ begin_test "migrate import --no-rewrite (with commit message)"
   prev_commit_oid="$(git rev-parse HEAD)"
   expected_commit_msg="run git-lfs migrate import --no-rewrite"
 
-  git lfs migrate import --message "$expected_commit_msg" --no-rewrite *.txt
+  git lfs migrate import --message "$expected_commit_msg" --no-rewrite --yes *.txt
 
   # Ensure the git history remained the same
   new_commit_oid="$(git rev-parse HEAD~1)"
@@ -201,7 +201,7 @@ begin_test "migrate import --no-rewrite (with empty commit message)"
 
   prev_commit_oid="$(git rev-parse HEAD)"
 
-  git lfs migrate import -m "" --no-rewrite *.txt
+  git lfs migrate import -m "" --no-rewrite --yes *.txt
 
   # Ensure the git history remained the same
   new_commit_oid="$(git rev-parse HEAD~1)"

test/test-migrate-import.sh

@@ -417,7 +417,7 @@ begin_test "migrate import (existing .gitattributes)"
 
   txt_master_oid="$(calc_oid "$(git cat-file -p "$master:a.txt")")"
 
-  git lfs migrate import --include-ref=refs/heads/master --include="*.txt"
+  git lfs migrate import --yes --include-ref=refs/heads/master --include="*.txt"
 
   assert_local_object "$txt_master_oid" "120"