[PATCH/RFCv4 1/2] git-rebase -i: add command "drop" to remove a commit

@@ -514,6 +514,9 @@ rebasing.
 If you just want to edit the commit message for a commit, replace the
 command "pick" with the command "reword".
 
+To drop a commit, replace the command "pick" with "drop", or just
+delete its line.
+
 If you want to fold two or more commits into one, replace the command
 "pick" for the second and subsequent commits with "squash" or "fixup".
 If the commits had different authors, the folded commit will be

@@ -152,6 +152,7 @@ Commands:
  s, squash = use commit, but meld into previous commit
  f, fixup = like "squash", but discard this commit's log message
  x, exec = run command (the rest of the line) using shell
+ d, drop = remove commit
 
 These lines can be re-ordered; they are executed from top to bottom.
 

@@ -508,6 +509,23 @@ do_next () {
 	"$comment_char"*|''|noop)
 		mark_action_done
 		;;
+	drop|d)
+		if test -z $sha1
+		then
+			warn "Missing SHA-1 in 'drop' command."
+			die "Please fix this using 'git rebase --edit-todo'."
+		fi
+
+		sha1_verif="$(git rev-parse --verify --quiet $sha1^{commit})"
+		if test -z $sha1_verif
+		then
+			warn "'$sha1' is not a SHA-1 or does not represent" \
+				"a commit in 'drop' command."
+			die "Please fix this using 'git rebase --edit-todo'."
+		fi
+
+		mark_action_done
+		;;
 	pick|p)
 		comment_for_reflog pick
 

@@ -14,7 +14,7 @@
 #       specified line.
 #
 #   "<cmd> <lineno>" -- add a line with the specified command
-#       ("squash", "fixup", "edit", or "reword") and the SHA1 taken
+#       ("squash", "fixup", "edit", "reword" or "drop") and the SHA1 taken
 #       from the specified line.
 #
 #   "exec_cmd_with_args" -- add an "exec cmd with args" line.

@@ -46,7 +46,7 @@ set_fake_editor () {
 	action=pick
 	for line in $FAKE_LINES; do
 		case $line in
-		squash|fixup|edit|reword)
+		squash|fixup|edit|reword|drop)
 			action="$line";;
 		exec*)
 			echo "$line" | sed 's/_/ /g' >> "$1";;

@@ -1102,4 +1102,14 @@ test_expect_success 'rebase -i commits that overwrite untracked files (no ff)' '
 	test $(git cat-file commit HEAD | sed -ne \$p) = I
 '
 
+test_expect_success 'drop' '
+	test_when_finished "git checkout master" &&
+	git checkout -b dropBranchTest master &&
+	set_fake_editor &&
+	FAKE_LINES="1 drop 2 3 drop 4 5" git rebase -i --root &&
+	test E = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test C = $(git cat-file commit HEAD^ | sed -ne \$p) &&
+	test A = $(git cat-file commit HEAD^^ | sed -ne \$p)
+'
+
 test_done

@@ -2160,6 +2160,16 @@ rebase.autoStash::
 	successful rebase might result in non-trivial conflicts.
 	Defaults to false.
 
+rebase.missingCommitsCheck::
+	If set to "warn", git rebase -i will print a warning if some
+	commits are removed (e.g. a line was deleted), however the
+	rebase will still proceed. If set to "error", it will print
+	the previous warning and abort the rebase. If set to
+	"ignore", no checking is done.
+	To drop a commit without warning or error, use the `drop`
+	command in the todo-list.
+	Defaults to "ignore".
+
 receive.advertiseAtomic::
 	By default, git-receive-pack will advertise the atomic push
 	capability to its clients. If you don't want to this capability

@@ -213,6 +213,12 @@ rebase.autoSquash::
 rebase.autoStash::
 	If set to true enable '--autostash' option by default.
 
+rebase.missingCommitsCheck::
+	If set to "warn" print warnings about removed commits in
+	interactive mode. If set to "error" print the warnings and
+	abort the rebase. If set to "ignore" no checking is
+	done. "ignore" by default.
+
 OPTIONS
 -------
 --onto <newbase>::

@@ -851,6 +851,86 @@ add_exec_commands () {
 	mv "$1.new" "$1"
 }
 
+# Print the list of the SHA-1 of the commits
+# from a todo list in a file.
+# $1: todo-file, $2: outfile
+todo_list_to_sha_list () {
+	git stripspace --strip-comments <"$1" | while read -r command sha1 rest
+	do
+		case $command in
+		x|"exec")
+			;;
+		*)
+			printf "%s\n" "$sha1"
+			;;
+		esac
+	done >"$2"
+}
+
+# Use warn for each line of a file
+# $1: file
+warn_file () {
+	while read -r line
+	do
+		warn " - $line"
+	done <"$1"
+}
+
+# Check if the user dropped some commits by mistake
+# Behaviour determined by rebase.missingCommitsCheck.
+check_commits () {
+	checkLevel=$(git config --get rebase.missingCommitsCheck)
+	checkLevel=${checkLevel:-ignore}
+	# Don't be case sensitive
+	checkLevel=$(echo "$checkLevel" | tr 'A-Z' 'a-z')
+
+	case "$checkLevel" in
+	warn|error)
+		# Get the SHA-1 of the commits
+		todo_list_to_sha_list "$todo".backup "$todo".oldsha1
+		todo_list_to_sha_list "$todo" "$todo".newsha1
+
+		# Sort the SHA-1 and compare them
+		sort -u "$todo".oldsha1 >"$todo".oldsha1+
+		mv "$todo".oldsha1+ "$todo".oldsha1
+		sort -u "$todo".newsha1 >"$todo".newsha1+
+		mv "$todo".newsha1+ "$todo".newsha1
+		comm -2 -3 "$todo".oldsha1 "$todo".newsha1 >"$todo".miss
+
+		# Make the list user-friendly
+		opt="--no-walk=sorted --format=oneline --abbrev-commit --stdin"
+		git rev-list $opt <"$todo".miss >"$todo".miss+
+		mv "$todo".miss+ "$todo".miss
+
+		# Check missing commits
+		if test -s "$todo".miss
+		then
+			warn "Warning: some commits may have been dropped" \
+				"accidentally."
+			warn "Dropped commits (newer to older):"
+			warn_file "$todo".miss
+			warn ""
+			warn "To avoid this message, use \"drop\" to" \
+				"explicitly remove a commit."
+			warn "Use git --config rebase.missingCommitsCheck to change" \
+				"the level of warnings (ignore, warn, error)."
+			warn ""
+
+			if test "$checkLevel" = error
+			then
+				die_abort "Rebase aborted due to dropped commits."
+			fi
+		fi
+		;;
+	ignore)
+		;;
+	*)
+		warn "Unrecognized setting $checkLevel for option" \
+			"rebase.missingCommitsCheck."
+		;;
+	esac
+}
+
 # The whole contents of this file is run by dot-sourcing it from
 # inside a shell function.  It used to be that "return"s we see
 # below were not inside any function, and expected to return

@@ -1096,6 +1176,8 @@ has_action "$todo" ||
 
 expand_todo_ids
 
+check_commits
+
 test -d "$rewritten" || test -n "$force_rebase" || skip_unnecessary_picks
 
 GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name"

@@ -1112,4 +1112,67 @@ test_expect_success 'drop' '
 	test A = $(git cat-file commit HEAD^^ | sed -ne \$p)
 '
 
+cat >expect <<EOF
+Successfully rebased and updated refs/heads/tmp2.
+EOF
+
+test_expect_success 'rebase -i respects rebase.missingCommitsCheck=ignore' '
+	test_config rebase.missingCommitsCheck ignore &&
+	test_when_finished "git checkout master &&
+		git branch -D tmp2" &&
+	git checkout -b tmp2 master &&
+	set_fake_editor &&
+	FAKE_LINES="1 2 3 4" \
+		git rebase -i --root 2>warning &&
+	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_cmp warning expect
+'
+
+cat >expect <<EOF
+Warning: some commits may have been dropped accidentally.
+Dropped commits (newer to older):
+ - $(git rev-list --pretty=oneline --abbrev-commit -1 master)
+
+To avoid this message, use "drop" to explicitly remove a commit.
+Use git --config rebase.missingCommitsCheck to change the level of warnings (ignore, warn, error).
+
+Successfully rebased and updated refs/heads/tmp2.
+EOF
+
+test_expect_success 'rebase -i respects rebase.missingCommitsCheck=warn' '
+	test_config rebase.missingCommitsCheck warn &&
+	test_when_finished "git checkout master &&
+		git branch -D tmp2" &&
+	git checkout -b tmp2 master &&
+	set_fake_editor &&
+	FAKE_LINES="1 2 3 4" \
+		git rebase -i --root 2>warning &&
+	test D = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_cmp warning expect
+'
+
+cat >expect <<EOF
+Warning: some commits may have been dropped accidentally.
+Dropped commits (newer to older):
+ - $(git rev-list --pretty=oneline --abbrev-commit -1 master)
+ - $(git rev-list --pretty=oneline --abbrev-commit -1 master~2)
+
+To avoid this message, use "drop" to explicitly remove a commit.
+Use git --config rebase.missingCommitsCheck to change the level of warnings (ignore, warn, error).
+
+Rebase aborted due to dropped commits.
+EOF
+
+test_expect_success 'rebase -i respects rebase.missingCommitsCheck=error' '
+	test_config rebase.missingCommitsCheck error &&
+	test_when_finished "git checkout master &&
+		git branch -D tmp2" &&
+	git checkout -b tmp2 master &&
+	set_fake_editor &&
+	test_must_fail env FAKE_LINES="1 2 4" \
+		git rebase -i --root 2>warning &&
+	test E = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test_cmp warning expect
+'
+
 test_done