Merge branch 'cc/replace-graft'

"git replace" learned a "--graft" option to rewrite parents of a
commit.

* cc/replace-graft:
  replace: add test for --graft with a mergetag
  replace: check mergetags when using --graft
  replace: add test for --graft with signed commit
  replace: remove signature when using --graft
  contrib: add convert-grafts-to-replace-refs.sh
  Documentation: replace: add --graft option
  replace: add test for --graft
  replace: add --graft option
  replace: cleanup redirection style in tests

Documentation/git-replace.txt

@@ -10,6 +10,7 @@ SYNOPSIS
 [verse]
 'git replace' [-f] <object> <replacement>
 'git replace' [-f] --edit <object>
+'git replace' [-f] --graft <commit> [<parent>...]
 'git replace' -d <object>...
 'git replace' [--format=<format>] [-l [<pattern>]]
 
@@ -81,6 +82,15 @@ OPTIONS
 	cannot be pretty-printed. Note that you may need to configure
 	your editor to cleanly read and write binary data.
 
+--graft <commit> [<parent>...]::
+	Create a graft commit. A new commit is created with the same
+	content as <commit> except that its parents will be
+	[<parent>...] instead of <commit>'s parents. A replacement ref
+	is then created to replace <commit> with the newly created
+	commit. See contrib/convert-grafts-to-replace-refs.sh for an
+	example script based on this option that can convert grafts to
+	replace refs.
+
 -l <pattern>::
 --list <pattern>::
 	List replace refs for objects that match the given pattern (or

builtin/replace.c

@@ -13,10 +13,12 @@
 #include "refs.h"
 #include "parse-options.h"
 #include "run-command.h"
+#include "tag.h"
 
 static const char * const git_replace_usage[] = {
 	N_("git replace [-f] <object> <replacement>"),
 	N_("git replace [-f] --edit <object>"),
+	N_("git replace [-f] --graft <commit> [<parent>...]"),
 	N_("git replace -d <object>..."),
 	N_("git replace [--format=<format>] [-l [<pattern>]]"),
 	NULL
@@ -299,6 +301,117 @@ static int edit_and_replace(const char *object_ref, int force, int raw)
 	return replace_object_sha1(object_ref, old, "replacement", new, force);
 }
 
+static void replace_parents(struct strbuf *buf, int argc, const char **argv)
+{
+	struct strbuf new_parents = STRBUF_INIT;
+	const char *parent_start, *parent_end;
+	int i;
+
+	/* find existing parents */
+	parent_start = buf->buf;
+	parent_start += 46; /* "tree " + "hex sha1" + "\n" */
+	parent_end = parent_start;
+
+	while (starts_with(parent_end, "parent "))
+		parent_end += 48; /* "parent " + "hex sha1" + "\n" */
+
+	/* prepare new parents */
+	for (i = 0; i < argc; i++) {
+		unsigned char sha1[20];
+		if (get_sha1(argv[i], sha1) < 0)
+			die(_("Not a valid object name: '%s'"), argv[i]);
+		lookup_commit_or_die(sha1, argv[i]);
+		strbuf_addf(&new_parents, "parent %s\n", sha1_to_hex(sha1));
+	}
+
+	/* replace existing parents with new ones */
+	strbuf_splice(buf, parent_start - buf->buf, parent_end - parent_start,
+		      new_parents.buf, new_parents.len);
+
+	strbuf_release(&new_parents);
+}
+
+struct check_mergetag_data {
+	int argc;
+	const char **argv;
+};
+
+static void check_one_mergetag(struct commit *commit,
+			       struct commit_extra_header *extra,
+			       void *data)
+{
+	struct check_mergetag_data *mergetag_data = (struct check_mergetag_data *)data;
+	const char *ref = mergetag_data->argv[0];
+	unsigned char tag_sha1[20];
+	struct tag *tag;
+	int i;
+
+	hash_sha1_file(extra->value, extra->len, typename(OBJ_TAG), tag_sha1);
+	tag = lookup_tag(tag_sha1);
+	if (!tag)
+		die(_("bad mergetag in commit '%s'"), ref);
+	if (parse_tag_buffer(tag, extra->value, extra->len))
+		die(_("malformed mergetag in commit '%s'"), ref);
+
+	/* iterate over new parents */
+	for (i = 1; i < mergetag_data->argc; i++) {
+		unsigned char sha1[20];
+		if (get_sha1(mergetag_data->argv[i], sha1) < 0)
+			die(_("Not a valid object name: '%s'"), mergetag_data->argv[i]);
+		if (!hashcmp(tag->tagged->sha1, sha1))
+			return; /* found */
+	}
+
+	die(_("original commit '%s' contains mergetag '%s' that is discarded; "
+	      "use --edit instead of --graft"), ref, sha1_to_hex(tag_sha1));
+}
+
+static void check_mergetags(struct commit *commit, int argc, const char **argv)
+{
+	struct check_mergetag_data mergetag_data;
+
+	mergetag_data.argc = argc;
+	mergetag_data.argv = argv;
+	for_each_mergetag(check_one_mergetag, commit, &mergetag_data);
+}
+
+static int create_graft(int argc, const char **argv, int force)
+{
+	unsigned char old[20], new[20];
+	const char *old_ref = argv[0];
+	struct commit *commit;
+	struct strbuf buf = STRBUF_INIT;
+	const char *buffer;
+	unsigned long size;
+
+	if (get_sha1(old_ref, old) < 0)
+		die(_("Not a valid object name: '%s'"), old_ref);
+	commit = lookup_commit_or_die(old, old_ref);
+
+	buffer = get_commit_buffer(commit, &size);
+	strbuf_add(&buf, buffer, size);
+	unuse_commit_buffer(commit, buffer);
+
+	replace_parents(&buf, argc - 1, &argv[1]);
+
+	if (remove_signature(&buf)) {
+		warning(_("the original commit '%s' has a gpg signature."), old_ref);
+		warning(_("the signature will be removed in the replacement commit!"));
+	}
+
+	check_mergetags(commit, argc, argv);
+
+	if (write_sha1_file(buf.buf, buf.len, commit_type, new))
+		die(_("could not write replacement commit for: '%s'"), old_ref);
+
+	strbuf_release(&buf);
+
+	if (!hashcmp(old, new))
+		return error("new commit is the same as the old one: '%s'", sha1_to_hex(old));
+
+	return replace_object_sha1(old_ref, old, "replacement", new, force);
+}
+
 int cmd_replace(int argc, const char **argv, const char *prefix)
 {
 	int force = 0;
@@ -309,12 +422,14 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 		MODE_LIST,
 		MODE_DELETE,
 		MODE_EDIT,
+		MODE_GRAFT,
 		MODE_REPLACE
 	} cmdmode = MODE_UNSPECIFIED;
 	struct option options[] = {
 		OPT_CMDMODE('l', "list", &cmdmode, N_("list replace refs"), MODE_LIST),
 		OPT_CMDMODE('d', "delete", &cmdmode, N_("delete replace refs"), MODE_DELETE),
 		OPT_CMDMODE('e', "edit", &cmdmode, N_("edit existing object"), MODE_EDIT),
+		OPT_CMDMODE('g', "graft", &cmdmode, N_("change a commit's parents"), MODE_GRAFT),
 		OPT_BOOL('f', "force", &force, N_("replace the ref if it exists")),
 		OPT_BOOL(0, "raw", &raw, N_("do not pretty-print contents for --edit")),
 		OPT_STRING(0, "format", &format, N_("format"), N_("use this format")),
@@ -332,7 +447,10 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 		usage_msg_opt("--format cannot be used when not listing",
 			      git_replace_usage, options);
 
-	if (force && cmdmode != MODE_REPLACE && cmdmode != MODE_EDIT)
+	if (force &&
+	    cmdmode != MODE_REPLACE &&
+	    cmdmode != MODE_EDIT &&
+	    cmdmode != MODE_GRAFT)
 		usage_msg_opt("-f only makes sense when writing a replacement",
 			      git_replace_usage, options);
 
@@ -359,6 +477,12 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 				      git_replace_usage, options);
 		return edit_and_replace(argv[0], force, raw);
 
+	case MODE_GRAFT:
+		if (argc < 1)
+			usage_msg_opt("-g needs at least one argument",
+				      git_replace_usage, options);
+		return create_graft(argc, argv, force);
+
 	case MODE_LIST:
 		if (argc > 1)
 			usage_msg_opt("only one pattern can be given with -l",

commit.c

@@ -1146,6 +1146,40 @@ int parse_signed_commit(const struct commit *commit,
 	return saw_signature;
 }
 
+int remove_signature(struct strbuf *buf)
+{
+	const char *line = buf->buf;
+	const char *tail = buf->buf + buf->len;
+	int in_signature = 0;
+	const char *sig_start = NULL;
+	const char *sig_end = NULL;
+
+	while (line < tail) {
+		const char *next = memchr(line, '\n', tail - line);
+		next = next ? next + 1 : tail;
+
+		if (in_signature && line[0] == ' ')
+			sig_end = next;
+		else if (starts_with(line, gpg_sig_header) &&
+			 line[gpg_sig_header_len] == ' ') {
+			sig_start = line;
+			sig_end = next;
+			in_signature = 1;
+		} else {
+			if (*line == '\n')
+				/* dump the whole remainder of the buffer */
+				next = tail;
+			in_signature = 0;
+		}
+		line = next;
+	}
+
+	if (sig_start)
+		strbuf_remove(buf, sig_start - buf->buf, sig_end - sig_start);
+
+	return sig_start != NULL;
+}
+
 static void handle_signed_tag(struct commit *parent, struct commit_extra_header ***tail)
 {
 	struct merge_remote_desc *desc;

commit.h

@@ -333,6 +333,8 @@ struct commit *get_merge_parent(const char *name);
 
 extern int parse_signed_commit(const struct commit *commit,
 			       struct strbuf *message, struct strbuf *signature);
+extern int remove_signature(struct strbuf *buf);
+
 extern void print_commit_list(struct commit_list *list,
 			      const char *format_cur,
 			      const char *format_last);

contrib/convert-grafts-to-replace-refs.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+# You should execute this script in the repository where you
+# want to convert grafts to replace refs.
+
+GRAFTS_FILE="${GIT_DIR:-.git}/info/grafts"
+
+. $(git --exec-path)/git-sh-setup
+
+test -f "$GRAFTS_FILE" || die "Could not find graft file: '$GRAFTS_FILE'"
+
+grep '^[^# ]' "$GRAFTS_FILE" |
+while read definition
+do
+	if test -n "$definition"
+	then
+		echo "Converting: $definition"
+		git replace --graft $definition ||
+			die "Conversion failed for: $definition"
+	fi
+done
+
+mv "$GRAFTS_FILE" "$GRAFTS_FILE.bak" ||
+	die "Could not rename '$GRAFTS_FILE' to '$GRAFTS_FILE.bak'"
+
+echo "Success!"
+echo "All the grafts in '$GRAFTS_FILE' have been converted to replace refs!"
+echo "The grafts file '$GRAFTS_FILE' has been renamed: '$GRAFTS_FILE.bak'"

t/t6050-replace.sh

@@ -7,6 +7,7 @@ test_description='Tests replace refs functionality'
 exec </dev/null
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
 
 add_and_commit_file ()
 {
@@ -18,6 +19,38 @@ add_and_commit_file()
     git commit --quiet -m "$_file: $_msg"
 }
 
+commit_buffer_contains_parents ()
+{
+    git cat-file commit "$1" >payload &&
+    sed -n -e '/^$/q' -e '/^parent /p' <payload >actual &&
+    shift &&
+    for _parent
+    do
+	echo "parent $_parent"
+    done >expected &&
+    test_cmp expected actual
+}
+
+commit_peeling_shows_parents ()
+{
+    _parent_number=1
+    _commit="$1"
+    shift &&
+    for _parent
+    do
+	_found=$(git rev-parse --verify $_commit^$_parent_number) || return 1
+	test "$_found" = "$_parent" || return 1
+	_parent_number=$(( $_parent_number + 1 ))
+    done &&
+    test_must_fail git rev-parse --verify $_commit^$_parent_number
+}
+
+commit_has_parents ()
+{
+    commit_buffer_contains_parents "$@" &&
+    commit_peeling_shows_parents "$@"
+}
+
 HASH1=
 HASH2=
 HASH3=
@@ -351,4 +384,60 @@ test_expect_success 'replace ref cleanup' '
 	test -z "$(git replace)"
 '
 
+test_expect_success '--graft with and without already replaced object' '
+	test $(git log --oneline | wc -l) = 7 &&
+	git replace --graft $HASH5 &&
+	test $(git log --oneline | wc -l) = 3 &&
+	commit_has_parents $HASH5 &&
+	test_must_fail git replace --graft $HASH5 $HASH4 $HASH3 &&
+	git replace --force -g $HASH5 $HASH4 $HASH3 &&
+	commit_has_parents $HASH5 $HASH4 $HASH3 &&
+	git replace -d $HASH5
+'
+
+test_expect_success GPG 'set up a signed commit' '
+	echo "line 17" >>hello &&
+	echo "line 18" >>hello &&
+	git add hello &&
+	test_tick &&
+	git commit --quiet -S -m "hello: 2 more lines in a signed commit" &&
+	HASH8=$(git rev-parse --verify HEAD) &&
+	git verify-commit $HASH8
+'
+
+test_expect_success GPG '--graft with a signed commit' '
+	git cat-file commit $HASH8 >orig &&
+	git replace --graft $HASH8 &&
+	git cat-file commit $HASH8 >repl &&
+	commit_has_parents $HASH8 &&
+	test_must_fail git verify-commit $HASH8 &&
+	sed -n -e "/^tree /p" -e "/^author /p" -e "/^committer /p" orig >expected &&
+	echo >>expected &&
+	sed -e "/^$/q" repl >actual &&
+	test_cmp expected actual &&
+	git replace -d $HASH8
+'
+
+test_expect_success GPG 'set up a merge commit with a mergetag' '
+	git reset --hard HEAD &&
+	git checkout -b test_branch HEAD~2 &&
+	echo "line 1 from test branch" >>hello &&
+	echo "line 2 from test branch" >>hello &&
+	git add hello &&
+	test_tick &&
+	git commit -m "hello: 2 more lines from a test branch" &&
+	HASH9=$(git rev-parse --verify HEAD) &&
+	git tag -s -m "tag for testing with a mergetag" test_tag HEAD &&
+	git checkout master &&
+	git merge -s ours test_tag &&
+	HASH10=$(git rev-parse --verify HEAD) &&
+	git cat-file commit $HASH10 | grep "^mergetag object"
+'
+
+test_expect_success GPG '--graft on a commit with a mergetag' '
+	test_must_fail git replace --graft $HASH10 $HASH8^1 &&
+	git replace --graft $HASH10 $HASH8^1 $HASH9 &&
+	git replace -d $HASH10
+'
+
 test_done