[PATCH] clone: do not segfault when specifying a nonexistent branch

[Stefan Beller <stefanbeller@googlemail.com>]

Actually I only wanted to change one line to prevent a crash, when you
specify a non existing branch when cloning:
-			if (option_branch) {
+			if (option_branch && our_head_points_at) {

However it turns out this is not a good idea as we still want to setup
'remote.*.fetch', which previously depended the string buffer 'value'
being non empty.
Therefore I added a local variable 'set_remote', which determines whether
we want to setup 'remote.*.fetch'.


While staring at the code, I also think it is a good idea to restructure
the if clauses a little as previously we had
	if (option_mirror || !option_bare) {
		if (option_single_branch && !option_mirror) {
The 'option_mirror' is part of both ifs, but opposing each other.
This is not yet done in this patch, as it still needs some thinking how to
remove the nesting of the if clauses in a nice way.

Reported-by: Robert Mitwicki <robert.mitwicki@opensoftware.pl>
Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
---
 builtin/clone.c | 50 ++++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 0aff974..8b9a78a 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -686,40 +686,46 @@ static void write_refspec_config(const char* src_ref_prefix,
 	struct strbuf key = STRBUF_INIT;
 	struct strbuf value = STRBUF_INIT;
 
+	int set_remote = 0;
 	if (option_mirror || !option_bare) {
+		set_remote = 1;
 		if (option_single_branch && !option_mirror) {
 			if (option_branch) {
-				if (strstr(our_head_points_at->name, "refs/tags/"))
-					strbuf_addf(&value, "+%s:%s", our_head_points_at->name,
-						our_head_points_at->name);
-				else
-					strbuf_addf(&value, "+%s:%s%s", our_head_points_at->name,
-						branch_top->buf, option_branch);
+				if (our_head_points_at) {
+					if (strstr(our_head_points_at->name, "refs/tags/"))
+						strbuf_addf(&value, "+%s:%s", our_head_points_at->name,
+							our_head_points_at->name);
+					else
+						strbuf_addf(&value, "+%s:%s%s", our_head_points_at->name,
+							branch_top->buf, option_branch);
+				}
 			} else if (remote_head_points_at) {
 				strbuf_addf(&value, "+%s:%s%s", remote_head_points_at->name,
 						branch_top->buf,
 						skip_prefix(remote_head_points_at->name, "refs/heads/"));
+			} else {
+				/*
+				 * otherwise, the next "git fetch" will
+				 * simply fetch from HEAD without updating
+				 * any remote-tracking branch, which is what
+				 * we want.
+				 */
+				set_remote = 0;
 			}
-			/*
-			 * otherwise, the next "git fetch" will
-			 * simply fetch from HEAD without updating
-			 * any remote-tracking branch, which is what
-			 * we want.
-			 */
 		} else {
 			strbuf_addf(&value, "+%s*:%s*", src_ref_prefix, branch_top->buf);
 		}
-		/* Configure the remote */
-		if (value.len) {
-			strbuf_addf(&key, "remote.%s.fetch", option_origin);
-			git_config_set_multivar(key.buf, value.buf, "^$", 0);
-			strbuf_reset(&key);
+	}
+	/* Configure the remote */
+	if (set_remote) {
+		strbuf_addf(&key, "remote.%s.fetch", option_origin);
+		git_config_set_multivar(key.buf, value.buf, "^$", 0);
+		strbuf_reset(&key);
 
-			if (option_mirror) {
-				strbuf_addf(&key, "remote.%s.mirror", option_origin);
-				git_config_set(key.buf, "true");
-				strbuf_reset(&key);
-			}
+		if (option_mirror) {
+			strbuf_addf(&key, "remote.%s.mirror", option_origin);
+			git_config_set(key.buf, "true");
+			strbuf_reset(&key);
 		}
 	}
 
-- 
1.8.4.1.469.gb38b9db