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+Date: Sat, 29 Sep 2012 19:58:30 -0400\r
+From: Austin Clements <amdragon@MIT.EDU>\r
+To: Jani Nikula <jani@nikula.org>\r
+Subject: Re: [PATCH] emacs: simplify point placement in notmuch-hello refresh\r
+Message-ID: <20120929235830.GZ26662@mit.edu>\r
+References: <1348958664-1767-1-git-send-email-jani@nikula.org>\r
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+\r
+LGTM. I wasn't aware notmuch-hello even attempted to maintain point,\r
+since I'd never seen it work.\r
+\r
+This patch could go a step further and remove found-target-pos from\r
+notmuch-hello-insert-saved-searches, target-pos from\r
+notmuch-hello-insert-searches, and found-target-pos from\r
+notmuch-hello-insert-buttons.\r
+\r
+It might be more stable to record the line number and column count and\r
+restore those, since point is sensitive to additions and removals of\r
+text within earlier lines.\r
+\r
+\r
+On a more abstract note, I feel like we have this same problem all\r
+over the Emacs UI: we "update" some UI by completely rebuilding it,\r
+and then we make some ad hoc, more-or-less (usually less) intelligent\r
+guess about where point should go. notmuch-hello has this problem,\r
+updating search-mode lines on tag change has this problem, refreshing\r
+the search buffer has this problem, and various buffer-rebuilding\r
+toggles in show have this problem.\r
+\r
+Proper incremental UI updates are simply not an option for some of\r
+these cases, because we have to call out to the CLI to get new data\r
+and that data might be completely different from what we're currently\r
+showing. We could restructure things to support this---for example,\r
+when toggling crypto, show could ask for the body of each message it's\r
+already showing---but this would complicate the code and I'm not sure\r
+we can restructure cases where the set of objects may change.\r
+\r
+But I wonder if there's an abstraction that would let us fully rebuild\r
+UIs or parts of UIs, but keep enough context to make this fluid. I'm\r
+imagining something like representing a buffer as a tree of UI nodes,\r
+where the buffer itself is simply the flattening of this tree, and\r
+each UI node has a identifier that's unique among its siblings. For\r
+example, the search buffer would have a root child for each search\r
+result, and then each piece of the result line would be a child of\r
+that line's node. This mechanism would give us a persistent context.\r
+Before an update, it could record the identifiers of all of the nodes\r
+in the path leading to the leaf node containing point, along with all\r
+of the prior siblings of each of these nodes and the offset of point\r
+within the leaf node. After and update, it could replay this path as\r
+best as possible: at each step in the path, if it can find a node with\r
+the same identifier as the node in the path, it would descend into it;\r
+otherwise, it would descend into the last recorded sibling it can find\r
+in the new tree. When this decent reaches a leaf, it can place point\r
+there. This same mechanism could be used to record and restore the\r
+window start position, as well as other markers we may need.\r
+\r
+Quoth Jani Nikula on Sep 30 at 1:44 am:\r
+> notmuch-hello (called also through notmuch-hello-update, bound to '='\r
+> by default) tries to find the widget under or following point before\r
+> refresh, and put the point back to the widget afterwards. The code has\r
+> grown quite complicated, and has at least the following issues:\r
+> \r
+> 1) All the individual section functions have to include code to\r
+> support point placement. If there is no such support, point is\r
+> dropped to the search box. Only saved searches and all tags\r
+> sections support point placement.\r
+> \r
+> 2) Point placement is based on widget-value. If there are two widgets\r
+> with the same widget-value (for example a saved search with the\r
+> same name as a tag) the point is moved to the earlier one, even if\r
+> point was on the later one.\r
+> \r
+> 3) When first entering notmuch-hello notmuch-hello-target is nil, and\r
+> point is dropped to the search box.\r
+> \r
+> Moving the point to the search box is annoying because the user is\r
+> required to move the point before being able to enter key bindings.\r
+> \r
+> Simplify the code by removing all point placement based on widgets, as\r
+> it does not work properly, and trying to fix that would unnecessarily\r
+> complicate the code.\r
+> \r
+> Point is simply saved before refresh, and put back to where it\r
+> was. Sometimes, if notmuch-show-empty-saved-searches is nil, and the\r
+> refresh adds or removes saved searches from the list, this has the\r
+> appearance of moving the point relative to the nearest widgets. This\r
+> is a much smaller and less frequent problem than the ones listed\r
+> above.\r
+> \r
+> ---\r
+> \r
+> I've sent this before months ago, and received comments starting at\r
+> id:"87aa2aohjs.fsf@gmail.com". I find the current behaviour annoying,\r
+> and I prefer this simple fix over complicating the existing\r
+> mess. Nobody has stood up to do anything better anyway. Perhaps we\r
+> could take a step forward with this while waiting for Someone(tm) to\r
+> come up with the perfect point placement?\r
+> ---\r
+> emacs/notmuch-hello.el | 70 ++++++++++++------------------------------------\r
+> 1 file changed, 17 insertions(+), 53 deletions(-)\r
+> \r
+> diff --git a/emacs/notmuch-hello.el b/emacs/notmuch-hello.el\r
+> index 684bedc..04d90cf 100644\r
+> --- a/emacs/notmuch-hello.el\r
+> +++ b/emacs/notmuch-hello.el\r
+> @@ -154,11 +154,6 @@ International Bureau of Weights and Measures."\r
+> (defvar notmuch-hello-url "http://notmuchmail.org"\r
+> "The `notmuch' web site.")\r
+> \r
+> -(defvar notmuch-hello-search-pos nil\r
+> - "Position of search widget, if any.\r
+> -\r
+> -This should only be set by `notmuch-hello-insert-search'.")\r
+> -\r
+> (defvar notmuch-hello-custom-section-options\r
+> '((:filter (string :tag "Filter for each tag"))\r
+> (:filter-count (string :tag "Different filter to generate message counts"))\r
+> @@ -209,11 +204,8 @@ function produces a section simply by adding content to the current\r
+> buffer. A section should not end with an empty line, because a\r
+> newline will be inserted after each section by `notmuch-hello'.\r
+> \r
+> -Each function should take no arguments. If the produced section\r
+> -includes `notmuch-hello-target' (i.e. cursor should be positioned\r
+> -inside this section), the function should return this element's\r
+> -position.\r
+> -Otherwise, it should return nil.\r
+> +Each function should take no arguments. The return value is\r
+> +ignored.\r
+> \r
+> For convenience an element can also be a list of the form (FUNC ARG1\r
+> ARG2 .. ARGN) in which case FUNC will be applied to the rest of the\r
+> @@ -240,15 +232,6 @@ supported for \"Customized queries section\" items."\r
+> notmuch-hello-query-section\r
+> (function :tag "Custom section"))))\r
+> \r
+> -(defvar notmuch-hello-target nil\r
+> - "Button text at position of point before rebuilding the notmuch-buffer.\r
+> -\r
+> -This variable contains the text of the button, if any, the\r
+> -point was positioned at before the notmuch-hello buffer was\r
+> -rebuilt. This should never actually be global and is defined as a\r
+> -defvar only for documentation purposes and to avoid a compiler\r
+> -warning about it occurring as a free variable.")\r
+> -\r
+> (defvar notmuch-hello-hidden-sections nil\r
+> "List of sections titles whose contents are hidden")\r
+> \r
+> @@ -449,8 +432,6 @@ Such a list can be computed with `notmuch-hello-query-counts'."\r
+> (msg-count (third elem)))\r
+> (widget-insert (format "%8s "\r
+> (notmuch-hello-nice-number msg-count)))\r
+> - (if (string= name notmuch-hello-target)\r
+> - (setq found-target-pos (point-marker)))\r
+> (widget-create 'push-button\r
+> :notify #'notmuch-hello-widget-search\r
+> :notmuch-search-terms query\r
+> @@ -589,7 +570,6 @@ Complete list of currently available key bindings:\r
+> (defun notmuch-hello-insert-search ()\r
+> "Insert a search widget."\r
+> (widget-insert "Search: ")\r
+> - (setq notmuch-hello-search-pos (point-marker))\r
+> (widget-create 'editable-field\r
+> ;; Leave some space at the start and end of the\r
+> ;; search boxes.\r
+> @@ -763,13 +743,7 @@ following:\r
+> (set-buffer "*notmuch-hello*")\r
+> (switch-to-buffer "*notmuch-hello*"))\r
+> \r
+> - (let ((notmuch-hello-target (if (widget-at)\r
+> - (widget-value (widget-at))\r
+> - (condition-case nil\r
+> - (progn\r
+> - (widget-forward 1)\r
+> - (widget-value (widget-at)))\r
+> - (error nil))))\r
+> + (let ((final-target-pos (point))\r
+> (inhibit-read-only t))\r
+> \r
+> ;; Delete all editable widget fields. Editable widget fields are\r
+> @@ -788,30 +762,20 @@ following:\r
+> (mapc 'delete-overlay (car all))\r
+> (mapc 'delete-overlay (cdr all)))\r
+> \r
+> - (let (final-target-pos)\r
+> - (mapc\r
+> - (lambda (section)\r
+> - (let ((point-before (point))\r
+> - (result (if (functionp section)\r
+> - (funcall section)\r
+> - (apply (car section) (cdr section)))))\r
+> - (if (and (not final-target-pos) (integer-or-marker-p result))\r
+> - (setq final-target-pos result))\r
+> - ;; don't insert a newline when the previous section didn't show\r
+> - ;; anything.\r
+> - (unless (eq (point) point-before)\r
+> - (widget-insert "\n"))))\r
+> - notmuch-hello-sections)\r
+> - (widget-setup)\r
+> -\r
+> - (when final-target-pos\r
+> - (goto-char final-target-pos)\r
+> - (unless (widget-at)\r
+> - (widget-forward 1)))\r
+> -\r
+> - (unless (widget-at)\r
+> - (when notmuch-hello-search-pos\r
+> - (goto-char notmuch-hello-search-pos)))))\r
+> + (mapc\r
+> + (lambda (section)\r
+> + (let ((point-before (point)))\r
+> + (if (functionp section)\r
+> + (funcall section)\r
+> + (apply (car section) (cdr section)))\r
+> + ;; don't insert a newline when the previous section didn't\r
+> + ;; show anything.\r
+> + (unless (eq (point) point-before)\r
+> + (widget-insert "\n"))))\r
+> + notmuch-hello-sections)\r
+> + (widget-setup)\r
+> +\r
+> + (goto-char final-target-pos))\r
+> (run-hooks 'notmuch-hello-refresh-hook)\r
+> (setq notmuch-hello-first-run nil))\r
+> \r
+\r
+-- \r
+Austin Clements MIT/'06/PhD/CSAIL\r
+amdragon@mit.edu http://web.mit.edu/amdragon\r
+ Somewhere in the dream we call reality you will find me,\r
+ searching for the reality we call dreams.\r
projects / notmuch-archives.git / commitdiff