scratch/icomplete-vertical-mode-improvements f7b22c0 08/10: Simplify icomplete-vertical-mode scrolling implementation

[João Távora]

branch: scratch/icomplete-vertical-mode-improvements
commit f7b22c08f81b768a552ae4b3a82a35fb0a777c15
Author: João Távora <joaotavora@gmail.com>
Commit: João Távora <joaotavora@gmail.com>

    Simplify icomplete-vertical-mode scrolling implementation
    
    * lisp/icomplete.el:
    (icomplete--last-selected, icomplete--comp-predecessors): Remove.
    (icomplete--scrolled-past, icomplete--scrolled-completions): New variables.
    (icomplete-forward-completions)
    (icomplete-backward-completions)
    (icomplete-minibuffer-setup):  Simplify.
    (icomplete-exhibit): Use new variable name.
    (icomplete--render-vertical): Simplify.
---
 lisp/icomplete.el | 44 +++++++++++++++++++++-----------------------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/lisp/icomplete.el b/lisp/icomplete.el
index 61129eb..b8ebb74 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -224,11 +224,13 @@ the default otherwise."
   (minibuffer-force-complete nil nil 'dont-cycle))
 
 ;; Both these variables are only meaningful if `icomplete-scroll' is
-;; non-nil.
-(defvar icomplete--comp-predecessors nil
-  "Completions to list before the selected one.")
-(defvar icomplete--last-selected nil
-  "Last completion explicitly selected.")
+;; non-nil.  We implement within classic rotating, non-scrolling
+;; icomplete by rotationg two lists (classic icomplete rotates only
+;; one list)
+(defvar icomplete--scrolled-past nil
+  "Completions manually scrolled past.")
+(defvar icomplete--scrolled-completions nil
+  "Completions manually scrolled to.")
 
 (defun icomplete-forward-completions ()
   "Step forward completions by one entry.
@@ -241,9 +243,8 @@ Second entry becomes the first and can be selected with
          (last (last comps)))
     (when (consp (cdr comps))
       (cond (icomplete-scroll
-             (push (pop comps) icomplete--comp-predecessors)
-             (setq icomplete--last-selected
-                   (cons (car comps) (buffer-modified-tick))))
+             (push (pop comps) icomplete--scrolled-past)
+             (setq icomplete--scrolled-completions comps))
             (t
              (setcdr (last comps) (cons (pop comps) (cdr last)))))
       (completion--cache-all-sorted-completions beg end comps))))
@@ -257,10 +258,9 @@ Last entry becomes the first and can be selected with
          (end (icomplete--field-end))
          (comps (completion-all-sorted-completions beg end))
         last-but-one)
-    (cond ((and icomplete-scroll icomplete--comp-predecessors)
-           (push (pop icomplete--comp-predecessors) comps)
-           (setq icomplete--last-selected
-                 (cons (car comps) (buffer-modified-tick))))
+    (cond ((and icomplete-scroll icomplete--scrolled-past)
+           (push (pop icomplete--scrolled-past) comps)
+           (setq icomplete--scrolled-completions comps))
           ((and (not icomplete-scroll)
                 (consp (cdr (setq last-but-one (last comps 2)))))
            ;; At least two elements in comps
@@ -475,7 +475,7 @@ Usually run by inclusion in `minibuffer-setup-hook'."
   (when (and icomplete-mode (icomplete-simple-completing-p))
     (setq-local icomplete--initial-input (icomplete--field-string))
     (setq-local completion-show-inline-help nil)
-    (setq icomplete--last-selected nil)
+    (setq icomplete--scrolled-completions nil)
     (use-local-map (make-composed-keymap icomplete-minibuffer-map
                                         (current-local-map)))
     (add-hook 'pre-command-hook  #'icomplete-pre-command-hook  nil t)
@@ -642,7 +642,7 @@ See `icomplete-mode' and `minibuffer-setup-hook'."
   (when (and icomplete-mode
              (icomplete-simple-completing-p)) ;Shouldn't be necessary.
     (unless completion-all-sorted-completions
-      (setq icomplete--comp-predecessors nil))
+      (setq icomplete--scrolled-past nil))
     (let ((saved-point (point)))
       (save-excursion
         (goto-char (point-max))
@@ -703,21 +703,19 @@ See `icomplete-mode' and `minibuffer-setup-hook'."
   ;; First, attempt to keep selection stable.  Do this only if
   ;; `icomplete-scroll' is t and there is a selection.
   ;;
-  ;; Most importantly, also only do this if the buffer changed,
-  ;; meaning there are new candidates within which we want to search
-  ;; for our manually selected one.  That's because if we were to
+  ;; Most importantly, also only if the new completions list doesn't
+  ;; match out manually scrolled list.  That's because if we were to
   ;; needlessly search for our selection in unchanged candidates, we'd
   ;; obviously always find it in the first position, lose the illusion
   ;; of a dropdown scroll.
   (when (and icomplete-scroll
-             icomplete--last-selected
-             (not (eq (cdr icomplete--last-selected) (buffer-modified-tick))))
+             (not (eq icomplete--scrolled-completions comps)))
     (cl-loop
      with preds
      for (comp . rest) on comps
-     when (equal comp (car icomplete--last-selected))
+     when (equal comp (car icomplete--scrolled-completions))
      do
-     (setq icomplete--comp-predecessors preds
+     (setq icomplete--scrolled-past preds
            comps (cons comp rest))
      (completion--cache-all-sorted-completions
       (icomplete--field-beg)
@@ -725,12 +723,12 @@ See `icomplete-mode' and `minibuffer-setup-hook'."
       comps)
      and return nil
      do (push comp preds)
-     finally (setq icomplete--last-selected nil)))
+     finally (setq icomplete--scrolled-completions nil)))
   ;; The ugliest loop, collect the completions before and after the
   ;; selected one, considering scrolling positions.
   ;;
   (cl-loop
-   with preds = icomplete--comp-predecessors
+   with preds = icomplete--scrolled-past
    with succs = (cdr comps)
    with max-lines = (1- (min icomplete-prospects-height
                              (max-mini-window-height)))