From 8fccb26cd3beccaf2f9664a928b99a8574f1cbd3 Mon Sep 17 00:00:00 2001
From: Matei Stroia <stroiamatei@gmail.com>
Date: Wed, 20 May 2026 14:56:39 +0300
Subject: [PATCH] fix(fold): virtual lines duplicate foldopen (#39891)

Problem:
Virtual lines above a line where a fold starts show `foldopen` in
`foldcolumn`.

Solution:
Check if the line below the virtual one is inside a fold that starts
higher up or if it's the start of a fold. In the latter case, don't show
anything in `foldcolumn` for the virtual line.

refactor: lint
(cherry picked from commit 526ae1cc1b432d7f1d9a412be86ac28c809f77eb)
---
 src/nvim/drawline.c              | 10 +++-
 test/functional/ui/fold_spec.lua | 98 ++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+), 1 deletion(-)

diff --git a/src/nvim/drawline.c b/src/nvim/drawline.c
index c8a0349e94..42188b52fb 100644
--- a/src/nvim/drawline.c
+++ b/src/nvim/drawline.c
@@ -486,7 +486,15 @@ static void draw_foldcolumn(win_T *wp, winlinevars_T *wlv)
   int fdc = compute_foldcolumn(wp, 0);
   if (fdc > 0) {
     int attr = win_hl_attr(wp, use_cursor_line_highlight(wp, wlv->lnum) ? HLF_CLF : HLF_FC);
-    fill_foldcolumn(wp, wlv->foldinfo, wlv->lnum, attr, fdc, &wlv->off, NULL, NULL);
+    // Only draw 'foldcolumn' for filler line if lnum is inside a fold that
+    // starts higher up. We don't want to show 'foldopen' or 'foldclose' twice.
+    foldinfo_T fi;
+    if (wlv->filler_todo <= 0 || wlv->foldinfo.fi_lnum < wlv->lnum) {
+      fi = wlv->foldinfo;
+    } else {
+      fi = (foldinfo_T){ 0 };
+    }
+    fill_foldcolumn(wp, fi, wlv->lnum, attr, fdc, &wlv->off, NULL, NULL);
   }
 }
 
diff --git a/test/functional/ui/fold_spec.lua b/test/functional/ui/fold_spec.lua
index aaff97fbe4..3b25f7cb7f 100644
--- a/test/functional/ui/fold_spec.lua
+++ b/test/functional/ui/fold_spec.lua
@@ -2257,6 +2257,104 @@ describe('folded lines', function()
       end
     end)
 
+    it('virt_lines above line where fold begins do not duplicate foldcolumn', function()
+      fn.setline(1, 'line 1')
+      fn.setline(2, 'line 2')
+      fn.setline(3, 'line 3')
+      fn.setline(4, 'line 4')
+
+      local ns = api.nvim_create_namespace('ns')
+      api.nvim_buf_set_extmark(
+        0,
+        ns,
+        1,
+        0,
+        { virt_lines_above = true, virt_lines = { { { 'above line 2' } } } }
+      )
+      api.nvim_buf_set_extmark(0, ns, 2, 0, { virt_lines = { { { 'below line 3' } } } })
+
+      command('set foldcolumn=1')
+      feed('jzfl')
+      feed('2jzfl')
+      if multigrid then
+        screen:expect([[
+        ## grid 1
+          [2:---------------------------------------------]|*7
+          [3:---------------------------------------------]|
+        ## grid 2
+          {7: }line 1                                      |
+          {7: }above line 2                                |
+          {7:-}line 2                                      |
+          {7: }line 3                                      |
+          {7: }below line 3                                |
+          {7:-}^line 4                                      |
+          {1:~                                            }|
+        ## grid 3
+                                                       |
+        ]])
+      else
+        screen:expect([[
+          {7: }line 1                                      |
+          {7: }above line 2                                |
+          {7:-}line 2                                      |
+          {7: }line 3                                      |
+          {7: }below line 3                                |
+          {7:-}^line 4                                      |
+          {1:~                                            }|
+                                                       |
+        ]])
+      end
+    end)
+
+    it('foldcolumn is not interrupted when virt_lines are inside a fold', function()
+      fn.setline(1, 'line 1')
+      fn.setline(2, 'line 2')
+      fn.setline(3, 'line 3')
+      fn.setline(4, 'line 4')
+
+      local ns = api.nvim_create_namespace('ns')
+      api.nvim_buf_set_extmark(0, ns, 1, 0, { virt_lines = { { { 'below line 2', '' } } } })
+      api.nvim_buf_set_extmark(
+        0,
+        ns,
+        2,
+        0,
+        { virt_lines_above = true, virt_lines = { { { 'above line 3', '' } } } }
+      )
+
+      command('set foldcolumn=1')
+      feed('zf2j')
+      feed('zo')
+      if multigrid then
+        screen:expect([[
+        ## grid 1
+          [2:---------------------------------------------]|*7
+          [3:---------------------------------------------]|
+        ## grid 2
+          {7:-}^line 1                                      |
+          {7:│}line 2                                      |
+          {7:│}below line 2                                |
+          {7:│}above line 3                                |
+          {7:│}line 3                                      |
+          {7: }line 4                                      |
+          {1:~                                            }|
+        ## grid 3
+                                                       |
+        ]])
+      else
+        screen:expect([[
+          {7:-}^line 1                                      |
+          {7:│}line 2                                      |
+          {7:│}below line 2                                |
+          {7:│}above line 3                                |
+          {7:│}line 3                                      |
+          {7: }line 4                                      |
+          {1:~                                            }|
+                                                       |
+        ]])
+      end
+    end)
+
     it('Folded and Visual highlights are combined #19691', function()
       command('hi! Visual guifg=NONE guibg=Red')
       insert([[