worktree: invoke post-checkout hook (unless --no-checkout)

git-clone and git-checkout both invoke the post-checkout hook following
a successful checkout, yet git-worktree neglects to do so even though it
too "checks out" the worktree. Fix this oversight.

Implementation note: The newly-created worktree may reference a branch
or be detached. In the latter case, a commit lookup is performed, though
the result is used only in a boolean sense to (a) determine if the
commit actually exists, and (b) assign either the branch name or commit
ID to HEAD. Since the post-commit hook needs to know the ID of the
checked-out commit, the lookup now needs to be done in all cases, rather
than only when detached. Consequently, a new boolean is needed to handle
(b) since the lookup result itself can no longer perform that role.

Reported-by: Matthew K Gumbel <matthew.k.gumbel@intel.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 0bb0042d8c..91eb297f7b 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -170,7 +170,8 @@ This hook cannot affect the outcome of 'git checkout'.
 
 It is also run after 'git clone', unless the --no-checkout (-n) option is
 used. The first parameter given to the hook is the null-ref, the second the
-ref of the new HEAD and the flag is always 1.
+ref of the new HEAD and the flag is always 1. Likewise for 'git worktree add'
+unless --no-checkout is used.
 
 This hook can be used to perform repository validity checks, auto-display
 differences from the previous HEAD if different, or set working dir metadata