[PATCH v3] More friendly message when locking the index fails.

[Matthieu Moy <Matthieu.Moy@imag.fr>]

Just saying that index.lock exists doesn't tell the user _what_ to do
to fix the problem. We should give an indication that it's normally
safe to delete index.lock after making sure git isn't running here.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
---
Oops, I hadn't noticed, but the previous version triggered a warning
because of lack of braces on the if. Sorry.

 builtin-update-index.c |   12 ++++++++++--
 lockfile.c             |   13 +++++++++++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/builtin-update-index.c b/builtin-update-index.c
index 5604977..23b97db 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -742,8 +742,16 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		if (newfd < 0) {
 			if (refresh_flags & REFRESH_QUIET)
 				exit(128);
-			die("unable to create '%s.lock': %s",
-			    get_index_file(), strerror(lock_error));
+			if (lock_error == EEXIST) {
+				die("Unable to create '%s.lock': %s.\n\n"
+				    "If no other git process is currently running, this probably means a\n"
+				    "git process crashed in this repository earlier. Make sure no other git\n"
+				    "process is running and remove the file manually to continue.",
+				    get_index_file(), strerror(lock_error));
+			} else {
+				die("Unable to create '%s.lock': %s",
+				    get_index_file(), strerror(lock_error));
+			}
 		}
 		if (write_cache(newfd, active_cache, active_nr) ||
 		    commit_locked_index(lock_file))
diff --git a/lockfile.c b/lockfile.c
index 021c337..c812596 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -158,8 +158,17 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
 {
 	int fd = lock_file(lk, path, flags);
-	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
-		die("unable to create '%s.lock': %s", path, strerror(errno));
+	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR)) {
+		if (errno == EEXIST) {
+			die("Unable to create '%s.lock': %s.\n\n"
+			    "If no other git process is currently running, this probably means a\n"
+			    "git process crashed in this repository earlier. Make sure no other git\n"
+			    "process is running and remove the file manually to continue.",
+			    path, strerror(errno));
+		} else {
+			die("Unable to create '%s.lock': %s", path, strerror(errno));
+		}
+	}
 	return fd;
 }
 
-- 
1.6.1.2.351.g80eb2.dirty