bug#52561: 28.0.50; [PATCH] Tall characters create scrolling stasis

[dick.r.chiang@gmail.com]

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After this prints "all bad", try M-v (scroll-down).

emacs-27.2 -Q --eval \
  "(progn \
     (switch-to-buffer \"xdisp-tests--scroll-down-leaves-cursor-behind\") \
     (insert \"Óscar\" \"\n\") \
     (dotimes (_ (/ (1+ (window-pixel-height)) (line-pixel-height))) \
        (insert \"line\" \"\n\")) \
     (goto-char (point-max)) \
     (redisplay) \
     (scroll-down) \
     (redisplay) \
     (princ (format \"all %s\n\" (if (= (window-start) 1) \"good\" \"bad\")) \
            (function external-debugging-output)))"



[-- Attachment #2: 0001-Tall-characters-create-scrolling-stasis.patch --]
[-- Type: text/x-diff, Size: 11160 bytes --]

From 8c6b54f2853d21f52fb729688436c0f765d7cbfe Mon Sep 17 00:00:00 2001
From: dickmao <dick.r.chiang@gmail.com>
Date: Thu, 16 Dec 2021 17:55:05 -0500
Subject: [PATCH] Tall characters create scrolling stasis

* lisp/emacs-lisp/multisession.el (multisession--set-value-sqlite):
You gotta do what you gotta do.
* src/xdisp.c (redisplay_window): VPOS is a screen line measure;
Y is a pixel measure.
* test/lisp/emacs-lisp/multisession-tests.el (multi-test--on-conflict-p):
You gotta do what you gotta do.
(multi-test-sqlite-simple): You gotta do what you gotta do.
(multi-test-sqlite-busy): You gotta do what you gotta do.
(multi-test-files-simple): You gotta do what you gotta do.
(multi-test-files-busy): You gotta do what you gotta do.
(multi-test-files-some-values): You gotta do what you gotta do.
* test/src/xdisp-tests.el (xdisp-tests--scroll-down-leaves-cursor-behind):
Test scrolling stasis bug.
---
 lisp/emacs-lisp/multisession.el            |  2 +
 src/xdisp.c                                | 33 ++++------
 test/lisp/emacs-lisp/multisession-tests.el | 77 ++++++++++++++--------
 test/src/xdisp-tests.el                    | 18 +++++
 4 files changed, 81 insertions(+), 49 deletions(-)

diff --git a/lisp/emacs-lisp/multisession.el b/lisp/emacs-lisp/multisession.el
index 17c9384134..5c77ac9a81 100644
--- a/lisp/emacs-lisp/multisession.el
+++ b/lisp/emacs-lisp/multisession.el
@@ -223,6 +223,8 @@ multisession--set-value-sqlite
       (condition-case nil
           (ignore (read-from-string pvalue))
         (error (error "Unable to store unreadable value: %s" pvalue)))
+      ;; I get near "ON" syntax error with 3.22.0
+      ;; https://stackoverflow.com/a/51531835/5132008
       (sqlite-execute
        multisession--db
        "insert into multisession(package, key, sequence, value) values(?, ?, 1, ?) on conflict(package, key) do update set sequence = sequence + 1, value = ?"
diff --git a/src/xdisp.c b/src/xdisp.c
index 5e549c9c63..65632ff167 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -18921,7 +18921,7 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
   if (w->force_start)
     {
       /* We set this later on if we have to adjust point.  */
-      int new_vpos = -1;
+      int new_y = -1;
 
       w->force_start = false;
       w->vscroll = 0;
@@ -18991,28 +18991,16 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
 				      NULL, 0);
 	    }
 	  if (r)
-	    new_vpos = MATRIX_ROW_BOTTOM_Y (r);
+	    new_y = MATRIX_ROW_BOTTOM_Y (r);
 	  else	/* Give up and just move to the middle of the window.  */
-	    new_vpos = window_box_height (w) / 2;
+	    new_y = window_box_height (w) / 2;
 	}
 
       if (!cursor_row_fully_visible_p (w, false, false, false))
 	{
 	  /* Point does appear, but on a line partly visible at end of window.
 	     Move it back to a fully-visible line.  */
-	  new_vpos = window_box_height (w);
-	  /* But if window_box_height suggests a Y coordinate that is
-	     not less than we already have, that line will clearly not
-	     be fully visible, so give up and scroll the display.
-	     This can happen when the default face uses a font whose
-	     dimensions are different from the frame's default
-	     font.  */
-	  if (new_vpos >= w->cursor.y)
-	    {
-	      w->cursor.vpos = -1;
-	      clear_glyph_matrix (w->desired_matrix);
-	      goto try_to_scroll;
-	    }
+	  new_y =  WINDOW_BOX_HEIGHT_NO_MODE_LINE (w);
 	}
       else if (w->cursor.vpos >= 0)
 	{
@@ -19052,13 +19040,18 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
 
       /* If we need to move point for either of the above reasons,
 	 now actually do it.  */
-      if (new_vpos >= 0)
+      if (new_y >= 0)
 	{
 	  struct glyph_row *row;
 
-	  row = MATRIX_FIRST_TEXT_ROW (w->desired_matrix);
-	  while (MATRIX_ROW_BOTTOM_Y (row) < new_vpos)
-	    ++row;
+	  for (row = MATRIX_FIRST_TEXT_ROW (w->desired_matrix);
+	       row < MATRIX_BOTTOM_TEXT_ROW (w->desired_matrix, w);
+	       ++row)
+	    if (MATRIX_ROW_BOTTOM_Y (row) - row->extra_line_spacing > new_y)
+	      {
+		row--;
+		break;
+	      }
 
 	  TEMP_SET_PT_BOTH (MATRIX_ROW_START_CHARPOS (row),
 			    MATRIX_ROW_START_BYTEPOS (row));
diff --git a/test/lisp/emacs-lisp/multisession-tests.el b/test/lisp/emacs-lisp/multisession-tests.el
index 41fcde04f2..8160f9115a 100644
--- a/test/lisp/emacs-lisp/multisession-tests.el
+++ b/test/lisp/emacs-lisp/multisession-tests.el
@@ -26,6 +26,13 @@
 (require 'ert-x)
 (require 'cl-lib)
 
+(defsubst multi-test--on-conflict-p ()
+  (when (bound-and-true-p multisession--db)
+    (let ((result (with-sqlite-transaction multisession--db
+		    (sqlite-select multisession--db "select sqlite_version()"))))
+      (version-list-<= (version-to-list "3.24.0")
+                       (version-to-list (seq-find #'stringp (cl-first result)))))))
+
 (ert-deftest multi-test-sqlite-simple ()
   (skip-unless (sqlite-available-p))
   (ert-with-temp-file dir
@@ -38,6 +45,7 @@ multi-test-sqlite-simple
             (define-multisession-variable foo 0
               ""
               :synchronized t)
+            (skip-unless (multi-test--on-conflict-p))
             (should (= (multisession-value foo) 0))
             (cl-incf (multisession-value foo))
             (should (= (multisession-value foo) 1))
@@ -56,11 +64,12 @@ multi-test-sqlite-simple
                               :synchronized t)
                             (cl-incf (multisession-value foo))))))
             (should (= (multisession-value foo) 2)))
-        (sqlite-close multisession--db)
+        (when multisession--db
+          (sqlite-close multisession--db))
         (setq multisession--db nil)))))
 
 (ert-deftest multi-test-sqlite-busy ()
-  (skip-unless (and t (sqlite-available-p)))
+  (skip-unless (sqlite-available-p))
   (ert-with-temp-file dir
     :directory t
     (let ((user-init-file "/tmp/foo.el")
@@ -72,6 +81,7 @@ multi-test-sqlite-busy
             (define-multisession-variable bar 0
               ""
               :synchronized t)
+            (skip-unless (multi-test--on-conflict-p))
             (should (= (multisession-value bar) 0))
             (cl-incf (multisession-value bar))
             (should (= (multisession-value bar) 1))
@@ -93,45 +103,53 @@ multi-test-sqlite-busy
                                     (cl-incf (multisession-value bar))))))))
             (while (process-live-p proc)
               (ignore-error 'sqlite-locked-error
-                (message "bar %s" (multisession-value bar))
-                ;;(cl-incf (multisession-value bar))
-                )
-              (sleep-for 0.1))
+                (message "bar %s" (multisession-value bar)))
+              (accept-process-output nil 0.1))
             (message "bar ends up as %s" (multisession-value bar))
             (should (< (multisession-value bar) 1003)))
-        (sqlite-close multisession--db)
+        (when (process-live-p proc)
+          (kill-process proc))
+        (when multisession--db
+          (sqlite-close multisession--db))
         (setq multisession--db nil)))))
 
 (ert-deftest multi-test-files-simple ()
+  (skip-unless (sqlite-available-p))
   (ert-with-temp-file dir
     :directory t
     (let ((user-init-file "/tmp/sfoo.el")
           (multisession-storage 'files)
           (multisession-directory dir))
-      (define-multisession-variable sfoo 0
-        ""
-        :synchronized t)
-      (should (= (multisession-value sfoo) 0))
-      (cl-incf (multisession-value sfoo))
-      (should (= (multisession-value sfoo) 1))
-      (call-process
-       (concat invocation-directory invocation-name)
-       nil t nil
-       "-Q" "-batch"
-       "--eval" (prin1-to-string
-                 `(progn
-                    (require 'multisession)
-                    (let ((multisession-directory ,dir)
-                          (multisession-storage 'files)
-                          (user-init-file "/tmp/sfoo.el"))
-                      (define-multisession-variable sfoo 0
-                        ""
-                        :synchronized t)
-                      (cl-incf (multisession-value sfoo))))))
-      (should (= (multisession-value sfoo) 2)))))
+      (unwind-protect
+          (progn
+            (define-multisession-variable sfoo 0
+              ""
+              :synchronized t)
+            (skip-unless (multi-test--on-conflict-p))
+            (should (= (multisession-value sfoo) 0))
+            (cl-incf (multisession-value sfoo))
+            (should (= (multisession-value sfoo) 1))
+            (call-process
+             (concat invocation-directory invocation-name)
+             nil t nil
+             "-Q" "-batch"
+             "--eval" (prin1-to-string
+                       `(progn
+                          (require 'multisession)
+                          (let ((multisession-directory ,dir)
+                                (multisession-storage 'files)
+                                (user-init-file "/tmp/sfoo.el"))
+                            (define-multisession-variable sfoo 0
+                              ""
+                              :synchronized t)
+                            (cl-incf (multisession-value sfoo))))))
+            (should (= (multisession-value sfoo) 2)))
+        (when multisession--db
+          (sqlite-close multisession--db))
+        (setq multisession--db nil)))))
 
 (ert-deftest multi-test-files-busy ()
-  (skip-unless (and t (sqlite-available-p)))
+  (skip-unless (sqlite-available-p))
   (ert-with-temp-file dir
     :directory t
     (let ((user-init-file "/tmp/foo.el")
@@ -168,6 +186,7 @@ multi-test-files-busy
       (should (< (multisession-value sbar) 2000)))))
 
 (ert-deftest multi-test-files-some-values ()
+  (skip-unless (sqlite-available-p))
   (ert-with-temp-file dir
     :directory t
     (let ((user-init-file "/tmp/sfoo.el")
diff --git a/test/src/xdisp-tests.el b/test/src/xdisp-tests.el
index ae4aacd9c7..f79406e531 100644
--- a/test/src/xdisp-tests.el
+++ b/test/src/xdisp-tests.el
@@ -170,4 +170,22 @@ test-get-display-property
     (should (equal (get-display-property 2 'height) 2.0))
     (should (equal (get-display-property 2 'space-width) 20))))
 
+(ert-deftest xdisp-tests--scroll-down-leaves-cursor-behind ()
+  "When first line contains accented, and therefore taller
+character, e.g., Óscar, scrolling down (moving window-start up)
+has resulted in a no-op."
+  (skip-unless (not noninteractive))
+  (switch-to-buffer "xdisp-tests--scroll-down-leaves-cursor-behind")
+
+  (insert "Óscar" "\n")
+  (dotimes (_ (/ (1+ (window-pixel-height)) (line-pixel-height)))
+    (insert "line" "\n"))
+  (goto-char (point-max))
+  (redisplay)
+  (scroll-down)
+  (redisplay)
+  (should (= (window-start) 1))
+  (let (kill-buffer-query-functions)
+    (kill-buffer "xdisp-tests--scroll-down-leaves-cursor-behind")))
+
 ;;; xdisp-tests.el ends here
-- 
2.26.2


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In Commercial Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30, cairo version 1.15.10)
 of 2021-12-16 built on dick
Repository revision: 2eb60be235d820a7e37ef37c23b6f5b10849f11c
Repository branch: dev
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.4 LTS

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