[PATCH 2/3] push: fail early with detached HEAD and current

[Ramkumar Ramachandra <artagnon@gmail.com>]

Setting push.default to current adds the refspec "HEAD" for the
transport layer to handle.  If "HEAD" doesn't resolve to a branch (and
since no refspec rhs is specified), the push fails after some time with
a cryptic error message:

  $ git push
  error: unable to push to unqualified destination: HEAD
  The destination refspec neither matches an existing ref on the remote nor
  begins with refs/, and we are unable to guess a prefix based on the source ref.
  error: failed to push some refs to 'git@github.com:artagnon/git'

Fail early with a nicer error message:

  $ git push
  fatal: You are not currently on a branch.
  To push the history leading to the current (detached HEAD)
  state now, use

    git push ram HEAD:<name-of-remote-branch>

Just like in the upstream and simple cases.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 builtin/push.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/builtin/push.c b/builtin/push.c
index ef3aa97..a79038c 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -175,6 +175,8 @@ static void warn_unspecified_push_default_configuration(void)
 
 static void setup_default_push_refspecs(struct remote *remote)
 {
+	struct branch *branch = branch_get(NULL);
+
 	switch (push_default) {
 	default:
 	case PUSH_DEFAULT_UNSPECIFIED:
@@ -194,6 +196,8 @@ static void setup_default_push_refspecs(struct remote *remote)
 		break;
 
 	case PUSH_DEFAULT_CURRENT:
+		if (!branch)
+			die(_(message_detached_head_die), remote->name);
 		add_refspec("HEAD");
 		break;
 
-- 
1.8.3.12.gbd56588