Merge branch 'maint'

* maint:
  Documentation: bisect: change a few instances of "git-cmd" to "git cmd"
  Documentation: rev-list: change a few instances of "git-cmd" to "git cmd"
  checkout: Don't crash when switching away from an invalid branch.

Documentation/git-bisect.txt

@@ -26,7 +26,7 @@ on the subcommand:
  git bisect log
  git bisect run <cmd>...
 
-This command uses 'git-rev-list --bisect' to help drive the
+This command uses 'git rev-list --bisect' to help drive the
 binary search process to find which change introduced a bug, given an
 old "good" commit object name and a later "bad" commit object name.
 
@@ -101,7 +101,7 @@ $ git bisect visualize
 to see the currently remaining suspects in 'gitk'.  `visualize` is a bit
 too long to type and `view` is provided as a synonym.
 
-If 'DISPLAY' environment variable is not set, 'git-log' is used
+If 'DISPLAY' environment variable is not set, 'git log' is used
 instead.  You can even give command line options such as `-p` and
 `--stat`.
 
@@ -215,7 +215,7 @@ tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or
 work around other problem this bisection is not interested in")
 applied to the revision being tested.
 
-To cope with such a situation, after the inner 'git-bisect' finds the
+To cope with such a situation, after the inner 'git bisect' finds the
 next revision to test, with the "run" script, you can apply that tweak
 before compiling, run the real test, and after the test decides if the
 revision (possibly with the needed tweaks) passed the test, rewind the

Documentation/rev-list-options.txt

@@ -285,7 +285,7 @@ See also linkgit:git-reflog[1].
 History Simplification
 ~~~~~~~~~~~~~~~~~~~~~~
 
-When optional paths are given, 'git-rev-list' simplifies commits with
+When optional paths are given, 'git rev-list' simplifies commits with
 various strategies, according to the options you have selected.
 
 Suppose you specified `foo` as the <paths>.  We shall call commits
@@ -466,14 +466,14 @@ Limit output to the one commit object which is roughly halfway between
 the included and excluded commits. Thus, if
 
 -----------------------------------------------------------------------
-	$ git-rev-list --bisect foo ^bar ^baz
+	$ git rev-list --bisect foo ^bar ^baz
 -----------------------------------------------------------------------
 
 outputs 'midpoint', the output of the two commands
 
 -----------------------------------------------------------------------
-	$ git-rev-list foo ^midpoint
-	$ git-rev-list midpoint ^bar ^baz
+	$ git rev-list foo ^midpoint
+	$ git rev-list midpoint ^bar ^baz
 -----------------------------------------------------------------------
 
 would be of roughly the same length.  Finding the change which

builtin-checkout.c

@@ -47,7 +47,7 @@ static int post_checkout_hook(struct commit *old, struct commit *new,
 
 	memset(&proc, 0, sizeof(proc));
 	argv[0] = name;
-	argv[1] = xstrdup(sha1_to_hex(old->object.sha1));
+	argv[1] = xstrdup(sha1_to_hex(old ? old->object.sha1 : null_sha1));
 	argv[2] = xstrdup(sha1_to_hex(new->object.sha1));
 	argv[3] = changed ? "1" : "0";
 	argv[4] = NULL;
@@ -492,10 +492,10 @@ static void update_refs_for_switch(struct checkout_opts *opts,
 	}
 
 	old_desc = old->name;
-	if (!old_desc)
+	if (!old_desc && old->commit)
 		old_desc = sha1_to_hex(old->commit->object.sha1);
 	strbuf_addf(&msg, "checkout: moving from %s to %s",
-		    old_desc, new->name);
+		    old_desc ? old_desc : "(invalid)", new->name);
 
 	if (new->path) {
 		create_symref("HEAD", new->path, msg.buf);
@@ -551,7 +551,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 	 * a new commit, we want to mention the old commit once more
 	 * to remind the user that it might be lost.
 	 */
-	if (!opts->quiet && !old.path && new->commit != old.commit)
+	if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
 		describe_detached_head("Previous HEAD position was", old.commit);
 
 	if (!old.commit) {

t/t2011-checkout-invalid-head.sh

+#!/bin/sh
+
+test_description='checkout switching away from an invalid branch'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo hello >world &&
+	git add world &&
+	git commit -m initial
+'
+
+test_expect_success 'checkout master from invalid HEAD' '
+	echo 0000000000000000000000000000000000000000 >.git/HEAD &&
+	git checkout master --
+'
+
+test_done