Merge branch 'jc/revert-merge'

* jc/revert-merge:
  cherry-pick/revert -m: add tests
  revert/cherry-pick: work on merge commits as well

Conflicts:

	builtin-revert.c

5 files changed, 181 insertions, 8 deletions

diff --git a/Documentation/git-cherry-pick.txt b/Documentation/git-cherry-pick.txt
index 76a2edf..937c4a7 100644
--- a/Documentation/git-cherry-pick.txt
+++ b/Documentation/git-cherry-pick.txt
@@ -7,7 +7,7 @@ git-cherry-pick - Apply the change introduced by an existing commit
 
 SYNOPSIS
 --------
-'git-cherry-pick' [--edit] [-n] [-x] <commit>
+'git-cherry-pick' [--edit] [-n] [-m parent-number] [-x] <commit>
 
 DESCRIPTION
 -----------
@@ -44,6 +44,13 @@ OPTIONS
 	described above, and `-r` was to disable it.  Now the
 	default is not to do `-x` so this option is a no-op.
 
+-m parent-number|--mainline parent-number::
+	Usually you cannot revert a merge because you do not know which
+	side of the merge should be considered the mainline.  This
+	option specifies the parent number (starting from 1) of
+	the mainline and allows cherry-pick to replay the change
+	relative to the specified parent.
+
 -n|--no-commit::
 	Usually the command automatically creates a commit with
 	a commit log message stating which commit was
diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
index 69db498..3457c40 100644
--- a/Documentation/git-revert.txt
+++ b/Documentation/git-revert.txt
@@ -7,7 +7,7 @@ git-revert - Revert an existing commit
 
 SYNOPSIS
 --------
-'git-revert' [--edit | --no-edit] [-n] <commit>
+'git-revert' [--edit | --no-edit] [-n] [-m parent-number] <commit>
 
 DESCRIPTION
 -----------
@@ -27,6 +27,13 @@ OPTIONS
 	message prior committing the revert. This is the default if
 	you run the command from a terminal.
 
+-m parent-number|--mainline parent-number::
+	Usually you cannot revert a merge because you do not know which
+	side of the merge should be considered the mainline.  This
+	option specifies the parent number (starting from 1) of
+	the mainline and allows revert to reverse the change
+	relative to the specified parent.
+
 --no-edit::
 	With this option, `git-revert` will not start the commit
 	message editor.
diff --git a/builtin-revert.c b/builtin-revert.c
index a9347cf..62ab1fa 100644
--- a/builtin-revert.c
+++ b/builtin-revert.c
@@ -30,7 +30,7 @@ static const char * const cherry_pick_usage[] = {
 	NULL
 };
 
-static int edit, no_replay, no_commit, needed_deref;
+static int edit, no_replay, no_commit, needed_deref, mainline;
 static enum { REVERT, CHERRY_PICK } action;
 static struct commit *commit;
 
@@ -50,12 +50,14 @@ static void parse_args(int argc, const char **argv)
 		OPT_BOOLEAN('e', "edit", &edit, "edit the commit message"),
 		OPT_BOOLEAN('x', NULL, &no_replay, "append commit name when cherry-picking"),
 		OPT_BOOLEAN('r', NULL, &noop, "no-op (backward compatibility)"),
+		OPT_INTEGER('m', "mainline", &mainline, "parent number"),
 		OPT_END(),
 	};
 
 	if (parse_options(argc, argv, options, usage_str, 0) != 1)
 		usage_with_options(usage_str, options);
 	arg = argv[0];
+
 	if (get_sha1(arg, sha1))
 		die ("Cannot find '%s'", arg);
 	commit = (struct commit *)parse_object(sha1);
@@ -226,7 +228,7 @@ static int merge_recursive(const char *base_sha1,
 static int revert_or_cherry_pick(int argc, const char **argv)
 {
 	unsigned char head[20];
-	struct commit *base, *next;
+	struct commit *base, *next, *parent;
 	int i;
 	char *oneline, *reencoded_message = NULL;
 	const char *message, *encoding;
@@ -261,8 +263,29 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 
 	if (!commit->parents)
 		die ("Cannot %s a root commit", me);
-	if (commit->parents->next)
-		die ("Cannot %s a multi-parent commit.", me);
+	if (commit->parents->next) {
+		/* Reverting or cherry-picking a merge commit */
+		int cnt;
+		struct commit_list *p;
+
+		if (!mainline)
+			die("Commit %s is a merge but no -m option was given.",
+			    sha1_to_hex(commit->object.sha1));
+
+		for (cnt = 1, p = commit->parents;
+		     cnt != mainline && p;
+		     cnt++)
+			p = p->next;
+		if (cnt != mainline || !p)
+			die("Commit %s does not have parent %d",
+			    sha1_to_hex(commit->object.sha1), mainline);
+		parent = p->item;
+	} else if (0 < mainline)
+		die("Mainline was specified but commit %s is not a merge.",
+		    sha1_to_hex(commit->object.sha1));
+	else
+		parent = commit->parents->item;
+
 	if (!(message = commit->buffer))
 		die ("Cannot get commit message for %s",
 				sha1_to_hex(commit->object.sha1));
@@ -291,14 +314,14 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 		char *oneline_body = strchr(oneline, ' ');
 
 		base = commit;
-		next = commit->parents->item;
+		next = parent;
 		add_to_msg("Revert \"");
 		add_to_msg(oneline_body + 1);
 		add_to_msg("\"\n\nThis reverts commit ");
 		add_to_msg(sha1_to_hex(commit->object.sha1));
 		add_to_msg(".\n");
 	} else {
-		base = commit->parents->item;
+		base = parent;
 		next = commit;
 		set_author_ident_env(message);
 		add_message_to_msg(message);
diff --git a/git-compat-util.h b/git-compat-util.h
index 474f1d1..7b29d1b 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -381,4 +381,17 @@ static inline int strtoul_ui(char const *s, int base, unsigned int *result)
 	return 0;
 }
 
+static inline int strtol_i(char const *s, int base, int *result)
+{
+	long ul;
+	char *p;
+
+	errno = 0;
+	ul = strtol(s, &p, base);
+	if (errno || *p || p == s || (int) ul != ul)
+		return -1;
+	*result = ul;
+	return 0;
+}
+
 #endif
diff --git a/t/t3502-cherry-pick-merge.sh b/t/t3502-cherry-pick-merge.sh
new file mode 100755
index 0000000..3274c61
--- /dev/null
+++ b/t/t3502-cherry-pick-merge.sh
@@ -0,0 +1,123 @@
+#!/bin/sh
+
+test_description='cherry picking and reverting a merge
+
+		b---c
+	       /   /
+	initial---a
+
+'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+
+	>A &&
+	>B &&
+	git add A B &&
+	git commit -m "Initial" &&
+	git tag initial &&
+	git branch side &&
+	echo new line >A &&
+	git commit -m "add line to A" A &&
+	git tag a &&
+	git checkout side &&
+	echo new line >B &&
+	git commit -m "add line to B" B &&
+	git tag b &&
+	git checkout master &&
+	git merge side &&
+	git tag c
+
+'
+
+test_expect_success 'cherry-pick a non-merge with -m should fail' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	! git cherry-pick -m 1 b &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'cherry pick a merge without -m should fail' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	! git cherry-pick c &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'cherry pick a merge (1)' '
+
+	git reset --hard &&
+	git checkout a^0 &&
+	git cherry-pick -m 1 c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'cherry pick a merge (2)' '
+
+	git reset --hard &&
+	git checkout b^0 &&
+	git cherry-pick -m 2 c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'cherry pick a merge relative to nonexistent parent should fail' '
+
+	git reset --hard &&
+	git checkout b^0 &&
+	! git cherry-pick -m 3 c
+
+'
+
+test_expect_success 'revert a non-merge with -m should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert -m 1 b &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'revert a merge without -m should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert c &&
+	git diff --exit-code c
+
+'
+
+test_expect_success 'revert a merge (1)' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	git revert -m 1 c &&
+	git diff --exit-code a
+
+'
+
+test_expect_success 'revert a merge (2)' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	git revert -m 2 c &&
+	git diff --exit-code b
+
+'
+
+test_expect_success 'revert a merge relative to nonexistent parent should fail' '
+
+	git reset --hard &&
+	git checkout c^0 &&
+	! git revert -m 3 c &&
+	git diff --exit-code c
+
+'
+
+test_done