Introduce CHERRY_PICK_HEAD

When a cherry-pick conflicts git advises:

 $ git commit -c <original commit id>

to preserve the original commit message and authorship. Instead, let's
record the original commit id in CHERRY_PICK_HEAD and advise:

  $ git commit -c CHERRY_PICK_HEAD

A later patch teaches git to handle the '-c CHERRY_PICK_HEAD' part.
Note that we record CHERRY_PICK_HEAD even in the case where there
are no conflicts so that we may use it to communicate authorship to
commit; this will then allow us to remove set_author_ident_env from
revert.c. However, we do not record CHERRY_PICK_HEAD when --no-commit
is used, as presumably the user intends to further edit the commit
and possibly even cherry-pick additional commits on top.

Tests and documentation contributed by Jonathan Nieder.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 25 insertions, 2 deletions

diff --git a/builtin/revert.c b/builtin/revert.c
index bb6e9e83b..e716a1b00 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -231,6 +231,22 @@ static void set_author_ident_env(const char *message)
 			sha1_to_hex(commit->object.sha1));
 }
 
+static void write_cherry_pick_head(void)
+{
+	int fd;
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_addf(&buf, "%s\n", sha1_to_hex(commit->object.sha1));
+
+	fd = open(git_path("CHERRY_PICK_HEAD"), O_WRONLY | O_CREAT, 0666);
+	if (fd < 0)
+		die_errno("Could not open '%s' for writing",
+			  git_path("CHERRY_PICK_HEAD"));
+	if (write_in_full(fd, buf.buf, buf.len) != buf.len || close(fd))
+		die_errno("Could not write to '%s'", git_path("CHERRY_PICK_HEAD"));
+	strbuf_release(&buf);
+}
+
 static void advise(const char *advice, ...)
 {
 	va_list params;
@@ -246,6 +262,12 @@ static void print_advice(void)
 
 	if (msg) {
 		fprintf(stderr, "%s\n", msg);
+		/*
+		 * A conflict has occured but the porcelain
+		 * (typically rebase --interactive) wants to take care
+		 * of the commit itself so remove CHERRY_PICK_HEAD
+		 */
+		unlink(git_path("CHERRY_PICK_HEAD"));
 		return;
 	}
 
@@ -253,8 +275,7 @@ static void print_advice(void)
 	advise("with 'git add <paths>' or 'git rm <paths>'");
 
 	if (action == CHERRY_PICK)
-		advise("and commit the result with 'git commit -c %s'",
-		       find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV));
+		advise("and commit the result with 'git commit -c CHERRY_PICK_HEAD'");
 }
 
 static void write_message(struct strbuf *msgbuf, const char *filename)
@@ -489,6 +510,8 @@ static int do_pick_commit(void)
 			strbuf_addstr(&msgbuf, sha1_to_hex(commit->object.sha1));
 			strbuf_addstr(&msgbuf, ")\n");
 		}
+		if (!no_commit)
+			write_cherry_pick_head();
 	}
 
 	if (!strategy || !strcmp(strategy, "recursive") || action == REVERT) {