[PATCH 1/6] builtin-commit: fix author date with --amend --author=<author>

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

When amending a commit with a new author, the author date is taken
from the original commit.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 builtin-commit.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/builtin-commit.c b/builtin-commit.c
index a84a729..6be6def 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -527,6 +527,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	} else if (amend) {
 		struct commit_list *c;
 		struct commit *commit;
+		const char *author;
 
 		reflog_msg = "commit (amend)";
 		commit = lookup_commit(head_sha1);
@@ -536,6 +537,21 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		for (c = commit->parents; c; c = c->next)
 			strbuf_addf(&sb, "parent %s\n",
 				      sha1_to_hex(c->item->object.sha1));
+
+		/* determine author date */
+		author = strstr(commit->buffer, "\nauthor");
+		if (author && !memmem(commit->buffer,
+					author + 1 - commit->buffer,
+					"\n\n", 2)) {
+			const char *email_end = strchr(author + 1, '>');
+			const char *line_end = strchr(author + 1, '\n');
+			if (email_end && line_end && email_end < line_end) {
+				char *date = xstrndup(email_end + 1,
+					line_end - email_end - 1);
+				setenv("GIT_AUTHOR_DATE", date, 1);
+				free(date);
+			}
+		}
 	} else if (in_merge) {
 		struct strbuf m;
 		FILE *fp;
-- 
1.5.3.5.1693.g26ed