[PATCH] 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>
---
> Perhaps it is a good idea to introduce
> 
> NORETURN void unable_to_lock_index_die(const char *path, int err)
> {
> 	if (err == EEXIST)
> 	        die(...);
>  	else
>         	die(...);
> }
> 
> in lockfile.c and call it from these two places you are touching?

Here it is!

 builtin-update-index.c |    3 +--
 cache.h                |    1 +
 lockfile.c             |   16 +++++++++++++++-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/builtin-update-index.c b/builtin-update-index.c
index 5604977..dd43d5b 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -742,8 +742,7 @@ 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));
+			unable_to_lock_index_die(get_index_file(), lock_error);
 		}
 		if (write_cache(newfd, active_cache, active_nr) ||
 		    commit_locked_index(lock_file))
diff --git a/cache.h b/cache.h
index 37dfb1c..bb5a190 100644
--- a/cache.h
+++ b/cache.h
@@ -484,6 +484,7 @@ struct lock_file {
 };
 #define LOCK_DIE_ON_ERROR 1
 #define LOCK_NODEREF 2
+extern NORETURN void unable_to_lock_index_die(const char *path, int err);
 extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
 extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
 extern int commit_lock_file(struct lock_file *);
diff --git a/lockfile.c b/lockfile.c
index 021c337..1db1a2f 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -155,11 +155,25 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 	return lk->fd;
 }
 
+
+NORETURN void unable_to_lock_index_die(const char *path, int err)
+{
+	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(err));
+	} else {
+		die("Unable to create '%s.lock': %s", path, strerror(err));
+	}
+}
+
 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));
+		unable_to_lock_index_die(path, errno);
 	return fd;
 }
 
-- 
1.6.2.rc1.14.g7f87d