patch 8.2.4660: cursorcolumn is sometimes not correctv8.2.4660

Problem:    Cursorcolumn is sometimes not correct.
Solution:   Recompute the cursor column when entering Insert mode and the
            cursor is on a character wider than a screen cell.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/testdir/test_highlight.vim b/src/testdir/test_highlight.vim
index b07ba1174..4b8cd86fa 100644
--- a/src/testdir/test_highlight.vim
+++ b/src/testdir/test_highlight.vim
@@ -592,6 +592,28 @@ func Test_cursorline_with_visualmode()
   call delete('Xtest_cursorline_with_visualmode')
 endfunc
 
+func Test_cursorcolumn_insert_on_tab()
+  CheckScreendump
+
+  let lines =<< trim END
+    call setline(1, ['123456789', "a\tb"])
+    set cursorcolumn
+    call cursor(2, 2)
+  END
+  call writefile(lines, 'Xcuc_insert_on_tab')
+
+  let buf = RunVimInTerminal('-S Xcuc_insert_on_tab', #{rows: 8})
+  call TermWait(buf)
+  call VerifyScreenDump(buf, 'Test_cursorcolumn_insert_on_tab_1', {})
+
+  call term_sendkeys(buf, 'i')
+  call TermWait(buf)
+  call VerifyScreenDump(buf, 'Test_cursorcolumn_insert_on_tab_2', {})
+
+  call StopVimInTerminal(buf)
+  call delete('Xcuc_insert_on_tab')
+endfunc
+
 func Test_cursorcolumn_callback()
   CheckScreendump
   CheckFeature timers