vim-patch:9.0.1543: display errors when making topline shorter

Problem:    Display errors when making topline shorter and 'smoothscroll' is
            set.
Solution:   Reset w_skipcol when the topline becomes shorter than its current
            value. (Luuk van Baal, closes vim/vim#12367)

https://github.com/vim/vim/commit/5d01f86d99bc3a3fd92d4f4e9338a9e78e9ebe16

5 files changed, 82 insertions, 12 deletions

diff --git a/src/nvim/change.c b/src/nvim/change.c
index 1d6869990e..a9e7126afc 100644
--- a/src/nvim/change.c
+++ b/src/nvim/change.c
@@ -247,11 +247,24 @@ static void changed_common(linenr_T lnum, colnr_T col, linenr_T lnume, linenr_T
         wp->w_redr_type = UPD_VALID;
       }
 
+      linenr_T last = lnume + xtra - 1;  // last line after the change
+
+      // Reset "w_skipcol" if the topline length has become smaller to
+      // such a degree that nothing will be visible anymore, accounting
+      // for 'smoothscroll' <<< or 'listchars' "precedes" marker.
+      if (wp->w_skipcol > 0
+          && (last < wp->w_topline
+              || (wp->w_topline >= lnum
+                  && wp->w_topline < lnume
+                  && win_linetabsize(wp, wp->w_topline, ml_get(wp->w_topline), (colnr_T)MAXCOL)
+                  <= (unsigned)wp->w_skipcol + (wp->w_p_list && wp->w_p_lcs_chars.prec ? 1 : 3)))) {
+        wp->w_skipcol = 0;
+      }
+
       // Check if a change in the buffer has invalidated the cached
       // values for the cursor.
       // Update the folds for this window.  Can't postpone this, because
       // a following operator might work on the whole fold: ">>dd".
-      linenr_T last = lnume + xtra - 1;  // last line after the change
       foldUpdate(wp, lnum, last);
 
       // The change may cause lines above or below the change to become
diff --git a/test/functional/legacy/display_spec.lua b/test/functional/legacy/display_spec.lua
index a698bed9f7..f59eac7674 100644
--- a/test/functional/legacy/display_spec.lua
+++ b/test/functional/legacy/display_spec.lua
@@ -200,13 +200,13 @@ describe('display', function()
     local screen = Screen.new(35, 14)
     screen:attach()
     exec([[
-      set display=lastline scrolloff=5
+      set display=lastline smoothscroll scrolloff=0
       call setline(1, [
-        \'aaaaa'->repeat(100),
+        \'aaaaa'->repeat(500),
         \'bbbbb '->repeat(7) .. 'ccccc '->repeat(7) .. 'ddddd '->repeat(7)
       \])
     ]])
-    feed('482|')
+    feed('736|')
     screen:expect([[
       <<<aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
@@ -219,10 +219,11 @@ describe('display', function()
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
-      aaaaaaaaaaaaaaaaaaaaaaaaaa^aaaaaaaaa|
-      aaaaaaaaaa                         |
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      ^aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
                                          |
     ]])
+    -- The correct part of the last line is moved into view.
     feed('D')
     screen:expect([[
       <<<aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
@@ -236,10 +237,48 @@ describe('display', function()
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
-      aaaaaaaaaaaaaaaaaaaaaaaaa^a         |
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa^a|
       bbbbb bbbbb bbbbb bbbbb bbbbb bb@@@|
                                          |
     ]])
+    -- "w_skipcol" does not change because the topline is still long enough
+    -- to maintain the current skipcol.
+    feed('g04l11gkD')
+    screen:expect([[
+      <<<^a                               |
+      bbbbb bbbbb bbbbb bbbbb bbbbb bbbbb|
+       bbbbb ccccc ccccc ccccc ccccc cccc|
+      c ccccc ccccc ddddd ddddd ddddd ddd|
+      dd ddddd ddddd ddddd               |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+      ~                                  |
+                                         |
+    ]])
+    -- "w_skipcol" is reset to bring the entire topline into view because
+    -- the line length is now smaller than the current skipcol + marker.
+    feed('x')
+    screen:expect([[
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
+      aa^a                                |
+      bbbbb bbbbb bbbbb bbbbb bbbbb bbbbb|
+       bbbbb ccccc ccccc ccccc ccccc cccc|
+      c ccccc ccccc ddddd ddddd ddddd @@@|
+                                         |
+    ]])
   end)
 
   -- oldtest: Test_display_cursor_long_line()
diff --git a/test/functional/legacy/scroll_opt_spec.lua b/test/functional/legacy/scroll_opt_spec.lua
index e567d238b2..838ada4006 100644
--- a/test/functional/legacy/scroll_opt_spec.lua
+++ b/test/functional/legacy/scroll_opt_spec.lua
@@ -588,6 +588,9 @@ describe('smoothscroll', function()
     -- than one window. Note that the cursor is at the bottom this time because
     -- Vim prefers to do so if we are scrolling a few lines only.
     exec("call setline(1, ['one', 'two', 'Line' .. (' with lots of text'->repeat(10)) .. ' end', 'four'])")
+    -- Currently visible lines were replaced, test that the lines and cursor
+    -- are correctly displayed.
+    screen:expect_unchanged()
     feed('3Gztj')
     screen:expect_unchanged()
     -- Repeat the step but this time start it when the line is smooth-scrolled by
diff --git a/test/old/testdir/test_display.vim b/test/old/testdir/test_display.vim
index b30f3bbeef..a2b40521d9 100644
--- a/test/old/testdir/test_display.vim
+++ b/test/old/testdir/test_display.vim
@@ -482,9 +482,9 @@ func Test_display_long_lastline()
   CheckScreendump
 
   let lines =<< trim END
-    set display=lastline
+    set display=lastline smoothscroll scrolloff=0
     call setline(1, [
-      \'aaaaa'->repeat(100),
+      \'aaaaa'->repeat(150),
       \'bbbbb '->repeat(7) .. 'ccccc '->repeat(7) .. 'ddddd '->repeat(7)
     \])
   END
@@ -492,11 +492,23 @@ func Test_display_long_lastline()
   call writefile(lines, 'XdispLongline', 'D')
   let buf = RunVimInTerminal('-S XdispLongline', #{rows: 14, cols: 35})
 
-  call term_sendkeys(buf, "482|")
+  call term_sendkeys(buf, "736|")
   call VerifyScreenDump(buf, 'Test_display_long_line_1', {})
+
+  " The correct part of the last line is moved into view.
   call term_sendkeys(buf, "D")
   call VerifyScreenDump(buf, 'Test_display_long_line_2', {})
 
+  " "w_skipcol" does not change because the topline is still long enough
+  " to maintain the current skipcol.
+  call term_sendkeys(buf, "g04l11gkD")
+  call VerifyScreenDump(buf, 'Test_display_long_line_3', {})
+
+  " "w_skipcol" is reset to bring the entire topline into view because
+  " the line length is now smaller than the current skipcol + marker.
+  call term_sendkeys(buf, "x")
+  call VerifyScreenDump(buf, 'Test_display_long_line_4', {})
+
   call StopVimInTerminal(buf)
 endfunc
 
diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index c0c3134ff4..6f3d12679e 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -335,9 +335,12 @@ func Test_smoothscroll_wrap_long_line()
   " than one window. Note that the cursor is at the bottom this time because
   " Vim prefers to do so if we are scrolling a few lines only.
   call term_sendkeys(buf, ":call setline(1, ['one', 'two', 'Line' .. (' with lots of text'->repeat(10)) .. ' end', 'four'])\<CR>")
+  " Currently visible lines were replaced, test that the lines and cursor
+  " are correctly displayed.
+  call VerifyScreenDump(buf, 'Test_smooth_long_14', {})
   call term_sendkeys(buf, "3Gzt")
   call term_sendkeys(buf, "j")
-  call VerifyScreenDump(buf, 'Test_smooth_long_14', {})
+  call VerifyScreenDump(buf, 'Test_smooth_long_15', {})
 
   " Repeat the step but this time start it when the line is smooth-scrolled by
   " one line. This tests that the offset calculation is still correct and
@@ -345,7 +348,7 @@ func Test_smoothscroll_wrap_long_line()
   " screen.
   call term_sendkeys(buf, "3Gzt")
   call term_sendkeys(buf, "\<C-E>j")
-  call VerifyScreenDump(buf, 'Test_smooth_long_15', {})
+  call VerifyScreenDump(buf, 'Test_smooth_long_16', {})
   
   call StopVimInTerminal(buf)
 endfunc