Merge branch 'jc/maint-co-track' into maint

* jc/maint-co-track:
  Enhance hold_lock_file_for_{update,append}() API
  demonstrate breakage of detached checkout with symbolic link HEAD
  Fix "checkout --track -b newbranch" on detached HEAD

Author: gitster

branch.c

@@ -129,7 +129,9 @@ void create_branch(const char *head,
 			die("Cannot setup tracking information; starting point is not a branch.");
 		break;
 	case 1:
-		/* Unique completion -- good */
+		/* Unique completion -- good, only if it is a real ref */
+		if (track == BRANCH_TRACK_EXPLICIT && !strcmp(real_ref, "HEAD"))
+			die("Cannot setup tracking information; starting point is not a branch.");
 		break;
 	default:
 		die("Ambiguous object name: '%s'.", start_name);

builtin-commit.c

@@ -320,7 +320,8 @@ static char *prepare_index(int argc, const char **argv, const char *prefix)
 		die("unable to write new_index file");
 
 	fd = hold_lock_file_for_update(&false_lock,
-				       git_path("next-index-%d", getpid()), 1);
+				       git_path("next-index-%d", getpid()),
+				       LOCK_DIE_ON_ERROR);
 
 	create_base_index();
 	add_remove_files(&partial);

builtin-fetch-pack.c

@@ -813,7 +813,8 @@ struct ref *fetch_pack(struct fetch_pack_args *my_args,
 			  )
 			die("shallow file was changed during fetch");
 
-		fd = hold_lock_file_for_update(&lock, shallow, 1);
+		fd = hold_lock_file_for_update(&lock, shallow,
+					       LOCK_DIE_ON_ERROR);
 		if (!write_shallow_commits(fd, 0)) {
 			unlink(shallow);
 			rollback_lock_file(&lock);

builtin-revert.c

@@ -338,7 +338,8 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 	 * reverse of it if we are revert.
 	 */
 
-	msg_fd = hold_lock_file_for_update(&msg_file, defmsg, 1);
+	msg_fd = hold_lock_file_for_update(&msg_file, defmsg,
+					   LOCK_DIE_ON_ERROR);
 
 	encoding = get_encoding(message);
 	if (!encoding)

bundle.c

@@ -186,7 +186,8 @@ int create_bundle(struct bundle_header *header, const char *path,
 	if (bundle_to_stdout)
 		bundle_fd = 1;
 	else
-		bundle_fd = hold_lock_file_for_update(&lock, path, 1);
+		bundle_fd = hold_lock_file_for_update(&lock, path,
+						      LOCK_DIE_ON_ERROR);
 
 	/* write signature */
 	write_or_die(bundle_fd, bundle_signature, strlen(bundle_signature));

cache.h

@@ -411,6 +411,8 @@ struct lock_file {
 	char on_list;
 	char filename[PATH_MAX];
 };
+#define LOCK_DIE_ON_ERROR 1
+#define LOCK_NODEREF 2
 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 *);

lockfile.c

@@ -121,15 +121,17 @@ static char *resolve_symlink(char *p, size_t s)
 }
 
 
-static int lock_file(struct lock_file *lk, const char *path)
+static int lock_file(struct lock_file *lk, const char *path, int flags)
 {
-	if (strlen(path) >= sizeof(lk->filename)) return -1;
+	if (strlen(path) >= sizeof(lk->filename))
+		return -1;
 	strcpy(lk->filename, path);
 	/*
 	 * subtract 5 from size to make sure there's room for adding
 	 * ".lock" for the lock file name
 	 */
-	resolve_symlink(lk->filename, sizeof(lk->filename)-5);
+	if (!(flags & LOCK_NODEREF))
+		resolve_symlink(lk->filename, sizeof(lk->filename)-5);
 	strcat(lk->filename, ".lock");
 	lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
 	if (0 <= lk->fd) {
@@ -155,35 +157,35 @@ static int lock_file(struct lock_file *lk, const char *path)
 	return lk->fd;
 }
 
-int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
+int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
 {
-	int fd = lock_file(lk, path);
-	if (fd < 0 && die_on_error)
+	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));
 	return fd;
 }
 
-int hold_lock_file_for_append(struct lock_file *lk, const char *path, int die_on_error)
+int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
 {
 	int fd, orig_fd;
 
-	fd = lock_file(lk, path);
+	fd = lock_file(lk, path, flags);
 	if (fd < 0) {
-		if (die_on_error)
+		if (flags & LOCK_DIE_ON_ERROR)
 			die("unable to create '%s.lock': %s", path, strerror(errno));
 		return fd;
 	}
 
 	orig_fd = open(path, O_RDONLY);
 	if (orig_fd < 0) {
 		if (errno != ENOENT) {
-			if (die_on_error)
+			if (flags & LOCK_DIE_ON_ERROR)
 				die("cannot open '%s' for copying", path);
 			close(fd);
 			return error("cannot open '%s' for copying", path);
 		}
 	} else if (copy_fd(orig_fd, fd)) {
-		if (die_on_error)
+		if (flags & LOCK_DIE_ON_ERROR)
 			exit(128);
 		close(fd);
 		return -1;
@@ -215,7 +217,10 @@ int commit_lock_file(struct lock_file *lk)
 
 int hold_locked_index(struct lock_file *lk, int die_on_error)
 {
-	return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
+	return hold_lock_file_for_update(lk, get_index_file(),
+					 die_on_error
+					 ? LOCK_DIE_ON_ERROR
+					 : 0);
 }
 
 void set_alternate_index_output(const char *name)

pack-refs.c

@@ -89,7 +89,8 @@ int pack_refs(unsigned int flags)
 	memset(&cbdata, 0, sizeof(cbdata));
 	cbdata.flags = flags;
 
-	fd = hold_lock_file_for_update(&packed, git_path("packed-refs"), 1);
+	fd = hold_lock_file_for_update(&packed, git_path("packed-refs"),
+				       LOCK_DIE_ON_ERROR);
 	cbdata.refs_file = fdopen(fd, "w");
 	if (!cbdata.refs_file)
 		die("unable to create ref-pack file structure (%s)",

refs.c

@@ -790,7 +790,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char
 	struct ref_lock *lock;
 	struct stat st;
 	int last_errno = 0;
-	int type;
+	int type, lflags;
 	int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
 
 	lock = xcalloc(1, sizeof(struct ref_lock));
@@ -830,8 +830,11 @@ static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char
 
 	lock->lk = xcalloc(1, sizeof(struct lock_file));
 
-	if (flags & REF_NODEREF)
+	lflags = LOCK_DIE_ON_ERROR;
+	if (flags & REF_NODEREF) {
 		ref = orig_ref;
+		lflags |= LOCK_NODEREF;
+	}
 	lock->ref_name = xstrdup(ref);
 	lock->orig_ref_name = xstrdup(orig_ref);
 	ref_file = git_path("%s", ref);
@@ -845,8 +848,8 @@ static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char
 		error("unable to create directory for %s", ref_file);
 		goto error_return;
 	}
-	lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, 1);
 
+	lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
 	return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
 
  error_return:

rerere.c

@@ -346,7 +346,8 @@ int setup_rerere(struct string_list *merge_rr)
 		return -1;
 
 	merge_rr_path = xstrdup(git_path("MERGE_RR"));
-	fd = hold_lock_file_for_update(&write_lock, merge_rr_path, 1);
+	fd = hold_lock_file_for_update(&write_lock, merge_rr_path,
+				       LOCK_DIE_ON_ERROR);
 	read_rr(merge_rr);
 	return fd;
 }