emacs: simplify point placement in notmuch-hello refresh

notmuch-hello (called also through notmuch-hello-update, bound to '='
by default) tries to find the widget under or following point before
refresh, and put the point back to the widget afterwards. The code has
grown quite complicated, and has at least the following issues:

1) All the individual section functions have to include code to
   support point placement. If there is no such support, point is
   dropped to the search box. Only saved searches and all tags
   sections support point placement.

2) Point placement is based on widget-value. If there are two widgets
   with the same widget-value (for example a saved search with the
   same name as a tag) the point is moved to the earlier one, even if
   point was on the later one.

3) When first entering notmuch-hello notmuch-hello-target is nil, and
   point is dropped to the search box.

Moving the point to the search box is annoying because the user is
required to move the point before being able to enter key bindings.

Simplify the code by removing all point placement based on widgets, as
it does not work properly, and trying to fix that would unnecessarily
complicate the code.

Save current line and column before refresh, and restore them
afterwards. Sometimes, if notmuch-show-empty-saved-searches is nil,
and the refresh adds or removes saved searches from the list, this has
the appearance of moving the point relative to the nearest
widgets. This is a much smaller and less frequent problem than the
ones listed above.

emacs/notmuch-hello.el

@@ -154,11 +154,6 @@ International Bureau of Weights and Measures."
 (defvar notmuch-hello-url "http://notmuchmail.org"
   "The `notmuch' web site.")
 
-(defvar notmuch-hello-search-pos nil
-  "Position of search widget, if any.
-
-This should only be set by `notmuch-hello-insert-search'.")
-
 (defvar notmuch-hello-custom-section-options
   '((:filter (string :tag "Filter for each tag"))
     (:filter-count (string :tag "Different filter to generate message counts"))
@@ -209,11 +204,8 @@ function produces a section simply by adding content to the current
 buffer.  A section should not end with an empty line, because a
 newline will be inserted after each section by `notmuch-hello'.
 
-Each function should take no arguments.  If the produced section
-includes `notmuch-hello-target' (i.e. cursor should be positioned
-inside this section), the function should return this element's
-position.
-Otherwise, it should return nil.
+Each function should take no arguments. The return value is
+ignored.
 
 For convenience an element can also be a list of the form (FUNC ARG1
 ARG2 .. ARGN) in which case FUNC will be applied to the rest of the
@@ -240,15 +232,6 @@ supported for \"Customized queries section\" items."
 	    notmuch-hello-query-section
 	    (function :tag "Custom section"))))
 
-(defvar notmuch-hello-target nil
-  "Button text at position of point before rebuilding the notmuch-buffer.
-
-This variable contains the text of the button, if any, the
-point was positioned at before the notmuch-hello buffer was
-rebuilt. This should never actually be global and is defined as a
-defvar only for documentation purposes and to avoid a compiler
-warning about it occurring as a free variable.")
-
 (defvar notmuch-hello-hidden-sections nil
   "List of sections titles whose contents are hidden")
 
@@ -435,8 +418,7 @@ Such a list can be computed with `notmuch-hello-query-counts'."
 	 (reordered-list (notmuch-hello-reflect searches tags-per-line))
 	 ;; Hack the display of the buttons used.
 	 (widget-push-button-prefix "")
-	 (widget-push-button-suffix "")
-	 (found-target-pos nil))
+	 (widget-push-button-suffix ""))
     ;; dme: It feels as though there should be a better way to
     ;; implement this loop than using an incrementing counter.
     (mapc (lambda (elem)
@@ -449,8 +431,6 @@ Such a list can be computed with `notmuch-hello-query-counts'."
 		     (msg-count (third elem)))
 		(widget-insert (format "%8s "
 				       (notmuch-hello-nice-number msg-count)))
-		(if (string= name notmuch-hello-target)
-		    (setq found-target-pos (point-marker)))
 		(widget-create 'push-button
 			       :notify #'notmuch-hello-widget-search
 			       :notmuch-search-terms query
@@ -466,8 +446,7 @@ Such a list can be computed with `notmuch-hello-query-counts'."
     ;; If the last line was not full (and hence did not include a
     ;; carriage return), insert one now.
     (unless (eq (% count tags-per-line) 0)
-      (widget-insert "\n"))
-    found-target-pos))
+      (widget-insert "\n"))))
 
 (defimage notmuch-hello-logo ((:type png :file "notmuch-logo.png")))
 
@@ -571,8 +550,7 @@ Complete list of currently available key bindings:
 		       (funcall notmuch-saved-search-sort-function
 				notmuch-saved-searches)
 		     notmuch-saved-searches)
-		   :show-empty-searches notmuch-show-empty-saved-searches))
-	found-target-pos)
+		   :show-empty-searches notmuch-show-empty-saved-searches)))
     (when searches
       (widget-insert "Saved searches: ")
       (widget-create 'push-button
@@ -581,15 +559,12 @@ Complete list of currently available key bindings:
 		     "edit")
       (widget-insert "\n\n")
       (let ((start (point)))
-	(setq found-target-pos
-	      (notmuch-hello-insert-buttons searches))
-	(indent-rigidly start (point) notmuch-hello-indent)
-	found-target-pos))))
+	(notmuch-hello-insert-buttons searches)
+	(indent-rigidly start (point) notmuch-hello-indent)))))
 
 (defun notmuch-hello-insert-search ()
   "Insert a search widget."
   (widget-insert "Search: ")
-  (setq notmuch-hello-search-pos (point-marker))
   (widget-create 'editable-field
 		 ;; Leave some space at the start and end of the
 		 ;; search boxes.
@@ -689,16 +664,13 @@ Supports the following entries in OPTIONS as a plist:
 				(notmuch-hello-update))
 		     "hide"))
     (widget-insert "\n")
-    (let (target-pos)
     (when (not is-hidden)
       (let ((searches (apply 'notmuch-hello-query-counts query-alist options)))
 	(when (or (not (plist-get options :hide-if-empty))
 		  searches)
 	  (widget-insert "\n")
-	    (setq target-pos
-		  (notmuch-hello-insert-buttons searches))
-	    (indent-rigidly start (point) notmuch-hello-indent))))
-      target-pos)))
+	  (notmuch-hello-insert-buttons searches)
+	  (indent-rigidly start (point) notmuch-hello-indent))))))
 
 (defun notmuch-hello-insert-tags-section (&optional title &rest options)
   "Insert a section displaying all tags with message counts.
@@ -763,13 +735,8 @@ following:
       (set-buffer "*notmuch-hello*")
     (switch-to-buffer "*notmuch-hello*"))
 
-  (let ((notmuch-hello-target (if (widget-at)
-				  (widget-value (widget-at))
-				(condition-case nil
-				    (progn
-				      (widget-forward 1)
-				      (widget-value (widget-at)))
-				  (error nil))))
+  (let ((target-line (line-number-at-pos))
+	(target-column (current-column))
 	(inhibit-read-only t))
 
     ;; Delete all editable widget fields.  Editable widget fields are
@@ -788,30 +755,25 @@ following:
       (mapc 'delete-overlay (car all))
       (mapc 'delete-overlay (cdr all)))
 
-    (let (final-target-pos)
     (mapc
      (lambda (section)
-	 (let ((point-before (point))
-	       (result (if (functionp section)
+       (let ((point-before (point)))
+	 (if (functionp section)
 	     (funcall section)
-			 (apply (car section) (cdr section)))))
-	   (if (and (not final-target-pos) (integer-or-marker-p result))
-	       (setq final-target-pos result))
-	   ;; don't insert a newline when the previous section didn't show
-	   ;; anything.
+	   (apply (car section) (cdr section)))
+	 ;; don't insert a newline when the previous section didn't
+	 ;; show anything.
 	 (unless (eq (point) point-before)
 	   (widget-insert "\n"))))
      notmuch-hello-sections)
     (widget-setup)
 
-      (when final-target-pos
-	(goto-char final-target-pos)
-	(unless (widget-at)
-	  (widget-forward 1)))
-
-      (unless (widget-at)
-	(when notmuch-hello-search-pos
-	  (goto-char notmuch-hello-search-pos)))))
+    ;; Move point back to where it was before refresh. Use line and
+    ;; column instead of point directly to be insensitive to additions
+    ;; and removals of text within earlier lines.
+    (goto-char (point-min))
+    (forward-line (1- target-line))
+    (move-to-column target-column))
   (run-hooks 'notmuch-hello-refresh-hook)
   (setq notmuch-hello-first-run nil))