feat(window/ui): add splitkeep option (#19243)

vim-patch:9.0.0445: when opening/closing window text moves up/down

Problem:    When opening/closing window text moves up/down.
Solution:   Add the 'splitscroll' option.  When off text will keep its
            position as much as possible.
https://github.com/vim/vim/commit/29ab524358ba429bcf6811710afc97a978641f0b

vim-patch:9.0.0455: a few problems with 'splitscroll'

Problem:    A few problems with 'splitscroll'.
Solution:   Fix 'splitscroll' problems. (Luuk van Baal, closes vim/vim#11117)
https://github.com/vim/vim/commit/5ed391708a62b4ebaa84dd23e32a416e5c3383d9

vim-patch:9.0.0461: 'scroll' is not always updated

Problem:    'scroll' is not always updated.
Solution:   Call win_init_size() at the right place.
https://github.com/vim/vim/commit/470a14140bc06f1653edf26ab0b3c9b801080353

vim-patch:9.0.0465: cursor moves when cmdwin is closed when 'splitscroll' is off

Problem:    Cursor moves when cmdwin is closed when 'splitscroll' is off.
Solution:   Temporarily set 'splitscroll' when jumping back to the original
            window. (closes vim/vim#11128)
https://github.com/vim/vim/commit/e697d488901b6321ddaad68b553f0a434c97d849

vim-patch:9.0.0469: cursor moves if cmdwin is closed when 'splitscroll' is off

Problem:    Cursor moves if cmdwin is closed when 'splitscroll' is off.
Solution:   Skip win_fix_cursor if called when cmdwin is open or closing.
            (Luuk van Baal, closes vim/vim#11134)
https://github.com/vim/vim/commit/3735f11050616652525bf80b4fbcb2b3bfeab113

vim-patch:9.0.0478: test for 'splitscroll' takes too much time

Problem:    Test for 'splitscroll' takes too much time.
Solution:   Only test some of the combinations. (Luuk van Baal, closes vim/vim#11139)
https://github.com/vim/vim/commit/594f9e09cd68e6277b8aa08094405bc642c5792a

vim-patch:9.0.0486: text scrolled with 'nosplitscroll', autocmd win and help

Problem:    Text scrolled with 'nosplitscroll', autocmd win opened and help
            window closed.
Solution:   Skip win_fix_scroll() in more situations. (Luuk van Baal,
            closes vim/vim#11150)
https://github.com/vim/vim/commit/d5bc762dea1fd32fa04342f8149f95ccfc3b9709

vim-patch:9.0.0505: various problems with 'nosplitscroll'

Problem:    Various problems with 'nosplitscroll'.
Solution:   Fix 'nosplitscroll' problems. (Luuk van Baal, closes vim/vim#11166)
https://github.com/vim/vim/commit/faf1d412f5e3665021500b528c0e7301eb02bf0b

vim-patch:9.0.0555: scrolling with 'nosplitscroll' in callback changing curwin

Problem:    Scrolling with 'nosplitscroll' in callback changing curwin.
Solution:   Invalidate w_cline_row in the right place. (Luuk van Baal,
            closes vim/vim#11185)
https://github.com/vim/vim/commit/20e58561abc4116f3bfbafaef242d886dd77b303

vim-patch:9.0.0603: with 'nosplitscroll' folds are not handled correctly

Problem:    With 'nosplitscroll' folds are not handled correctly.
Solution:   Take care of closed folds when moving the cursor. (Luuk van Baal,
            closes vim/vim#11234)
https://github.com/vim/vim/commit/7c1cbb6cd437c6e0c3ccc05840cc931108b4a60a

vim-patch:9.0.0605: dump file missing

Problem:    Dump file missing.
Solution:   Add the missing dump file. (issue vim/vim#11234)
https://github.com/vim/vim/commit/439a2ba1749463718b6ce1e1375b68c7b7cff808

vim-patch:9.0.0647: the 'splitscroll' option is not a good name

Problem:    The 'splitscroll' option is not a good name.
Solution:   Rename 'splitscroll' to 'splitkeep' and make it a string option,
            also supporting "topline". (Luuk van Baal, closes vim/vim#11258)
https://github.com/vim/vim/commit/13ece2ae1d09009d3fb8acf858c288e7848ecdac

vim-patch:9.0.0667: ml_get error when 'splitkeep' is "screen"

Problem:    ml_get error when 'splitkeep' is "screen". (Marius Gedminas)
Solution:   Check the botline is not too large. (Luuk van Baal,
            closes vim/vim#11293, closes vim/vim#11292)
https://github.com/vim/vim/commit/346823d3e5668b99d2c2fd920e7f215e21ad3ea7

1 files changed, 82 insertions, 67 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 781e9e3553..09f20baebf 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -2541,97 +2541,112 @@ int oneleft(void)
   return OK;
 }
 
-/// @oaram upd_topline  When true: update topline
-int cursor_up(long n, int upd_topline)
+/// Move the cursor up "n" lines in window "wp".
+/// Takes care of closed folds.
+/// Returns the new cursor line or zero for failure.
+linenr_T cursor_up_inner(win_T *wp, long n)
 {
-  linenr_T lnum;
+  linenr_T lnum = wp->w_cursor.lnum;
 
-  if (n > 0) {
-    lnum = curwin->w_cursor.lnum;
-
-    // This fails if the cursor is already in the first line.
-    if (lnum <= 1) {
-      return FAIL;
-    }
-    if (n >= lnum) {
-      lnum = 1;
-    } else if (hasAnyFolding(curwin)) {
-      // Count each sequence of folded lines as one logical line.
+  // This fails if the cursor is already in the first line.
+  if (lnum <= 1) {
+    return 0;
+  }
+  if (n >= lnum) {
+    lnum = 1;
+  } else if (hasAnyFolding(wp)) {
+    // Count each sequence of folded lines as one logical line.
 
-      // go to the start of the current fold
-      (void)hasFolding(lnum, &lnum, NULL);
+    // go to the start of the current fold
+    (void)hasFoldingWin(wp, lnum, &lnum, NULL, true, NULL);
 
-      while (n--) {
-        // move up one line
-        lnum--;
-        if (lnum <= 1) {
-          break;
-        }
-        // If we entered a fold, move to the beginning, unless in
-        // Insert mode or when 'foldopen' contains "all": it will open
-        // in a moment.
-        if (n > 0 || !((State & MODE_INSERT) || (fdo_flags & FDO_ALL))) {
-          (void)hasFolding(lnum, &lnum, NULL);
-        }
+    while (n--) {
+      // move up one line
+      lnum--;
+      if (lnum <= 1) {
+        break;
       }
-      if (lnum < 1) {
-        lnum = 1;
+      // If we entered a fold, move to the beginning, unless in
+      // Insert mode or when 'foldopen' contains "all": it will open
+      // in a moment.
+      if (n > 0 || !((State & MODE_INSERT) || (fdo_flags & FDO_ALL))) {
+        (void)hasFoldingWin(wp, lnum, &lnum, NULL, true, NULL);
       }
-    } else {
-      lnum -= (linenr_T)n;
     }
-    curwin->w_cursor.lnum = lnum;
+    if (lnum < 1) {
+      lnum = 1;
+    }
+  } else {
+    lnum -= (linenr_T)n;
+  }
+
+  wp->w_cursor.lnum = lnum;
+  return lnum;
+}
+
+/// @param upd_topline  When true: update topline
+int cursor_up(long n, int upd_topline)
+{
+  if (n > 0 && cursor_up_inner(curwin, n) == 0) {
+    return FAIL;
   }
 
   // try to advance to the column we want to be at
   coladvance(curwin->w_curswant);
 
   if (upd_topline) {
-    update_topline(curwin);           // make sure curwin->w_topline is valid
+    update_topline(curwin);  // make sure curwin->w_topline is valid
   }
 
   return OK;
 }
 
-/// Cursor down a number of logical lines.
-///
-/// @param upd_topline  When true: update topline
-int cursor_down(long n, int upd_topline)
+/// Move the cursor down "n" lines in window "wp".
+/// Takes care of closed folds.
+/// Returns the new cursor line or zero for failure.
+linenr_T cursor_down_inner(win_T *wp, long n)
 {
-  linenr_T lnum;
-
-  if (n > 0) {
-    lnum = curwin->w_cursor.lnum;
-    // Move to last line of fold, will fail if it's the end-of-file.
-    (void)hasFolding(lnum, NULL, &lnum);
+  linenr_T lnum = wp->w_cursor.lnum;
+  linenr_T line_count = wp->w_buffer->b_ml.ml_line_count;
 
-    // This fails if the cursor is already in the last line.
-    if (lnum >= curbuf->b_ml.ml_line_count) {
-      return FAIL;
-    }
-    if (lnum + n >= curbuf->b_ml.ml_line_count) {
-      lnum = curbuf->b_ml.ml_line_count;
-    } else if (hasAnyFolding(curwin)) {
-      linenr_T last;
+  // Move to last line of fold, will fail if it's the end-of-file.
+  (void)hasFoldingWin(wp, lnum, NULL, &lnum, true, NULL);
+  // This fails if the cursor is already in the last line.
+  if (lnum >= line_count) {
+    return FAIL;
+  }
+  if (lnum + n >= line_count) {
+    lnum = line_count;
+  } else if (hasAnyFolding(wp)) {
+    linenr_T last;
 
-      // count each sequence of folded lines as one logical line
-      while (n--) {
-        if (hasFolding(lnum, NULL, &last)) {
-          lnum = last + 1;
-        } else {
-          lnum++;
-        }
-        if (lnum >= curbuf->b_ml.ml_line_count) {
-          break;
-        }
+    // count each sequence of folded lines as one logical line
+    while (n--) {
+      if (hasFoldingWin(wp, lnum, NULL, &last, true, NULL)) {
+        lnum = last + 1;
+      } else {
+        lnum++;
       }
-      if (lnum > curbuf->b_ml.ml_line_count) {
-        lnum = curbuf->b_ml.ml_line_count;
+      if (lnum >= line_count) {
+        break;
       }
-    } else {
-      lnum += (linenr_T)n;
     }
-    curwin->w_cursor.lnum = lnum;
+    if (lnum > line_count) {
+      lnum = line_count;
+    }
+  } else {
+    lnum += (linenr_T)n;
+  }
+
+  wp->w_cursor.lnum = lnum;
+  return lnum;
+}
+
+/// @param upd_topline  When true: update topline
+int cursor_down(long n, int upd_topline)
+{
+  if (n > 0 && cursor_down_inner(curwin, n) == 0) {
+    return FAIL;
   }
 
   // try to advance to the column we want to be at