bug#52302: 28.0.50; [PATCH] Overlay strings should not increment vpos

[dick.r.chiang@gmail.com]

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From 010b26de2993754db6bb42243b5c6c89fc5e8a50 Mon Sep 17 00:00:00 2001
From: dickmao <dick.r.chiang@gmail.com>
Date: Sun, 5 Dec 2021 12:25:32 -0500
Subject: [PATCH] Overlay strings at `to_charpos` should not increment vpos

Previously, two calls to `move_it_vertically_backward (it, 0)` were
required to get IT back to line start.  It should only ever
take one call.

* src/xdisp.c (move_it_to): Recognize the invisible overlay
string should not increment vpos.
(move_it_vertically_backward): Rectify assertions.
(resize_mini_window): Should not need to call
move_it_vertically_backward (it, 0) twice.
* test/src/xdisp-tests.el (xdisp-tests--minibuffer-resizing):
Test.
---
 src/xdisp.c             | 28 ++++++++++++----------------
 test/src/xdisp-tests.el | 30 +++++++++++++-----------------
 2 files changed, 25 insertions(+), 33 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 0ff6286af74..e5498bbbb1b 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -10081,6 +10081,7 @@ move_it_to (struct it *it, ptrdiff_t to_charpos, int to_x, int to_y, int to_vpos
 
   for (;;)
     {
+      bool reached_continued = false;
       orig_charpos = IT_CHARPOS (*it);
       orig_method = it->method;
       if (op & MOVE_TO_VPOS)
@@ -10125,6 +10126,11 @@ move_it_to (struct it *it, ptrdiff_t to_charpos, int to_x, int to_y, int to_vpos
 		      break;
 		    }
 		}
+	      else if (skip == MOVE_LINE_CONTINUED
+		       && it->method == GET_FROM_STRING
+		       && IT_CHARPOS (*it) == to_charpos)
+		/* TO_CHARPOS reached, now consuming overlay string. */
+		reached_continued = true;
 	    }
 	}
       else if (op & MOVE_TO_Y)
@@ -10381,7 +10387,8 @@ move_it_to (struct it *it, ptrdiff_t to_charpos, int to_x, int to_y, int to_vpos
       it->hpos = 0;
       it->line_number_produced_p = false;
       it->current_y += it->max_ascent + it->max_descent;
-      ++it->vpos;
+      if (! reached_continued)
+	++it->vpos;
       last_height = it->max_ascent + it->max_descent;
       it->max_ascent = it->max_descent = 0;
     }
@@ -10490,11 +10497,11 @@ move_it_vertically_backward (struct it *it, int dy)
 	   || (it2.method == GET_FROM_STRING
 	       && IT_CHARPOS (it2) == start_pos
 	       && SREF (it2.string, IT_STRING_BYTEPOS (it2) - 1) == '\n')));
-  eassert (IT_CHARPOS (*it) >= BEGV);
+  eassert (IT_CHARPOS (it2) >= BEGV);
   SAVE_IT (it3, it2, it3data);
 
   move_it_to (&it2, start_pos, -1, -1, -1, MOVE_TO_POS);
-  eassert (IT_CHARPOS (*it) >= BEGV);
+  eassert (IT_CHARPOS (it2) >= BEGV);
   /* H is the actual vertical distance from the position in *IT
      and the starting position.  */
   h = it2.current_y - it->current_y;
@@ -12218,7 +12225,6 @@ resize_mini_window (struct window *w, bool exact_p)
       struct it it;
       int unit = FRAME_LINE_HEIGHT (f);
       int height, max_height;
-      struct text_pos start;
       struct buffer *old_current_buffer = NULL;
       int windows_height = FRAME_INNER_HEIGHT (f);
 
@@ -12272,25 +12278,15 @@ resize_mini_window (struct window *w, bool exact_p)
 	    {
 	      init_iterator (&it, w, ZV, ZV_BYTE, NULL, DEFAULT_FACE_ID);
 	      move_it_vertically_backward (&it, height - unit);
-              /* The following move is usually a no-op when the stuff
-                 displayed in the mini-window comes entirely from buffer
-                 text, but it is needed when some of it comes from overlay
-                 strings, especially when there's an after-string at ZV.
-                 This happens with some completion packages, like
-                 icomplete, ido-vertical, etc.  With those packages, if we
-                 don't force w->start to be at the beginning of a screen
-                 line, important parts of the stuff in the mini-window,
-                 such as user prompt, will be hidden from view.  */
-              move_it_by_lines (&it, 0);
-              start = it.current.pos;
               /* Prevent redisplay_window from recentering, and thus from
                  overriding the window-start point we computed here.  */
               w->start_at_line_beg = false;
-              SET_MARKER_FROM_TEXT_POS (w->start, start);
+              SET_MARKER_FROM_TEXT_POS (w->start, it.current.pos);
             }
 	}
       else
 	{
+	  struct text_pos start;
 	  SET_TEXT_POS (start, BEGV, BEGV_BYTE);
           SET_MARKER_FROM_TEXT_POS (w->start, start);
         }
diff --git a/test/src/xdisp-tests.el b/test/src/xdisp-tests.el
index ae4aacd9c7c..d1d7262665a 100644
--- a/test/src/xdisp-tests.el
+++ b/test/src/xdisp-tests.el
@@ -34,23 +34,19 @@ xdisp-tests--in-minibuffer
 
 (ert-deftest xdisp-tests--minibuffer-resizing () ;; bug#43519
   (should
-   (equal
-    t
-    (xdisp-tests--in-minibuffer
-      (insert "hello")
-      (let ((ol (make-overlay (point) (point)))
-            (max-mini-window-height 1)
-            (text "askdjfhaklsjdfhlkasjdfhklasdhflkasdhflkajsdhflkashdfkljahsdlfkjahsdlfkjhasldkfhalskdjfhalskdfhlaksdhfklasdhflkasdhflkasdhflkajsdhklajsdgh"))
-        ;; (save-excursion (insert text))
-        ;; (sit-for 2)
-        ;; (delete-region (point) (point-max))
-        (put-text-property 0 1 'cursor t text)
-        (overlay-put ol 'after-string text)
-        (redisplay 'force)
-        ;; Make sure we do the see "hello" text.
-        (prog1 (equal (window-start) (point-min))
-          ;; (list (window-start) (window-end) (window-width))
-          (delete-overlay ol)))))))
+   (xdisp-tests--in-minibuffer
+    (insert "hello")
+    (let ((ol (make-overlay (point) (point)))
+          (max-mini-window-height 1)
+          (text (let ((s ""))
+                  (dotimes (i 137)
+                    (setq s (concat s (char-to-string (+ (% i 26) ?a)))))
+                  s)))
+      (put-text-property 0 1 'cursor t text)
+      (overlay-put ol 'after-string text)
+      (redisplay)
+      (prog1 (equal (window-start) (point-min))
+        (delete-overlay ol))))))
 
 (ert-deftest xdisp-tests--minibuffer-scroll () ;; bug#44070
   (let ((posns
-- 
2.26.2


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