emacs: replace use of hook to draw hl-line in search mode

In the thread at id:87fsfuuxwn.fsf@thinkbox, a bug is discussed where
the point and hl-line overlay get out of sync, leading the user to
open the wrong message. As far as I can tell this is caused by
notmuch-hl-mode being invoked too early.

This change bypasses the logic preventing notmuch-search-hook being
called only once, so that the overlay is updated later after the
buffer is full(er).

This change may lead to the overlay being updated multiple times; if
this is annoying we can add a similar buffer local variable to ensure
it is only called once.

The extra logic to check notmuch-search-target-line reduces the
flicker somewhat by not highlighting the first line every time.

2 files changed, 11 insertions, 4 deletions

diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index 934ec894..5477bf4a 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -126,10 +126,9 @@ there will be called at other points of notmuch execution."
   :type 'file
   :group 'notmuch)
 
-(defcustom notmuch-search-hook '(notmuch-hl-line-mode)
+(defcustom notmuch-search-hook nil
   "List of functions to call when notmuch displays the search results."
   :type 'hook
-  :options '(notmuch-hl-line-mode)
   :group 'notmuch-search
   :group 'notmuch-hooks)
 
@@ -930,6 +929,16 @@ sets the :orig-tag property."
 	(notmuch-sexp-parse-partial-list 'notmuch-search-append-result
 					 results-buf))
       (with-current-buffer results-buf
+	(when (and notmuch-hl-line
+		   ;; If we know where the cursor will end up (from
+		   ;; the call to notmuch-search), avoid redrawing the
+		   ;; hl-line overlay until the buffer is sufficiently
+		   ;; filled. This check is intended as an
+		   ;; optimization to reduce flicker.
+		   (>=
+		    (line-number-at-pos (point-max) t)
+		    (or notmuch-search-target-line -1)))
+	  (notmuch-hl-line-mode))
 	(notmuch--search-hook-wrapper)))))
 
 ;;; Commands (and some helper functions used by them)
diff --git a/test/T312-emacs-hl-line.sh b/test/T312-emacs-hl-line.sh
index 4cceed30..4697b671 100755
--- a/test/T312-emacs-hl-line.sh
+++ b/test/T312-emacs-hl-line.sh
@@ -104,7 +104,6 @@ test_emacs_expect_t '(let ((notmuch-hl-line t))
 			   (line-number-at-pos (overlay-start hl-line-overlay)) 12))'
 
 test_begin_subtest "line 12, search, refresh"
-test_subtest_known_broken
 test_emacs_expect_t '(let ((notmuch-hl-line t))
 			(notmuch-search "tag:inbox")
 			(notmuch-test-wait)
@@ -140,7 +139,6 @@ test_emacs_expect_t '(let ((notmuch-hl-line t))
 			   (line-number-at-pos (overlay-start hl-line-overlay)) 12))'
 
 test_begin_subtest "hl-line disabled, search"
-test_subtest_known_broken
 test_emacs_expect_t '(let ((notmuch-hl-line nil))
 			(notmuch-search "tag:inbox")
 			(notmuch-test-wait)