From 79a7a4abe11f9b678cbf7073a4464fbe8631d57a Mon Sep 17 00:00:00 2001
From: Jaehwang Jung <tomtomjhj@gmail.com>
Date: Sun, 19 Apr 2026 02:16:31 +0900
Subject: [PATCH 1/2] fix(smoothscroll): crash when resizing to textoff with
 showbreak

vim-patch:9.2.0362: division by zero with smoothscroll and small windows

Problem:  Resizing a smoothscrolled wrapped window to its textoff width
          with 'showbreak' can leave wrapped continuation lines with
          zero text width. win_lbr_chartabsize() still runs the partial max_head_vcol calculation in
          that state and divides by width2, crashing during redraw.
Solution: Skip that partial head calculation when the wrapped
          continuation width is zero, matching the other width2 guards
          in charset.c (Jaehwang Jung)

closes: vim/vim#20012

AI-assisted: Codex

https://github.com/vim/vim/commit/0e31fb024c846e36bb0d26d01ff179a0d1b3eae4
---
 src/nvim/plines.c                          |  2 +-
 test/functional/legacy/scroll_opt_spec.lua | 18 ++++++++++
 test/old/testdir/test_scroll_opt.vim       | 38 ++++++++++++++++++++++
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/nvim/plines.c b/src/nvim/plines.c
index 1fafdf2206..12b40c1a5a 100644
--- a/src/nvim/plines.c
+++ b/src/nvim/plines.c
@@ -269,7 +269,7 @@ CharSize charsize_regular(CharsizeArg *csarg, char *const cur, colnr_T const vco
 
         if (max_head_vcol == 0 || vcol + size + added < max_head_vcol) {
           head += cnt * head_mid;
-        } else if (max_head_vcol > vcol + head_prev + prev_rem) {
+        } else if (width2 > 0 && max_head_vcol > vcol + head_prev + prev_rem) {
           head += (max_head_vcol - (vcol + head_prev + prev_rem)
                    + width2 - 1) / width2 * head_mid;
         } else if (max_head_vcol < 0) {
diff --git a/test/functional/legacy/scroll_opt_spec.lua b/test/functional/legacy/scroll_opt_spec.lua
index 427a69ca01..16f061a5c7 100644
--- a/test/functional/legacy/scroll_opt_spec.lua
+++ b/test/functional/legacy/scroll_opt_spec.lua
@@ -1127,6 +1127,24 @@ describe('smoothscroll', function()
     screen:expect(screen_l_top)
   end)
 
+  -- oldtest: Test_smoothscroll_textoff_showbreak()
+  it('does not crash when resizing to textoff with showbreak', function()
+    exec([[
+      set noswapfile scrolloff=0
+
+      call setline(1, 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa')
+      set number wrap smoothscroll showbreak=>
+      vsplit
+
+      let textoff = getwininfo(win_getid())[0].textoff
+      execute "normal! 0\<C-E>"
+      redraw
+      execute 'vertical resize' textoff
+      redraw
+    ]])
+    assert_alive()
+  end)
+
   it('works with virt_lines above and below', function()
     screen:try_resize(55, 7)
     exec([=[
diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index 4db7db2a49..7c65afa38b 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -1443,4 +1443,42 @@ func Test_smoothscroll_listchars_eol()
   bwipe!
 endfunc
 
+
+" Resizing to "textoff" after 'smoothscroll' skips part of a wrapped line must
+" not crash.
+func Test_smoothscroll_textoff_showbreak()
+  CheckOption smoothscroll
+
+  let donefile = 'XTest_crash_textoff_showbreak_done'
+  defer delete(donefile)
+  let lines =<< trim END
+    set noswapfile
+
+    set scrolloff=0
+    set lines=12 columns=40
+
+    call setline(1, 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa')
+    set number wrap smoothscroll showbreak=>
+    vsplit
+
+    let textoff = getwininfo(win_getid())[0].textoff
+    execute "normal! 0\<C-E>"
+    redraw
+    execute 'vertical resize' textoff
+    redraw
+    call writefile(['done'], 'XTest_crash_textoff_showbreak_done')
+  END
+  call writefile(lines, 'XTest_crash_textoff_showbreak', 'D')
+
+  let buf = 0
+  let buf = term_start([GetVimProg(), '--clean'], #{term_rows: 24, term_cols: 80})
+  call TermWait(buf, 200)
+  call term_sendkeys(buf, ":source XTest_crash_textoff_showbreak\<CR>")
+  call WaitForAssert({-> assert_true(filereadable(donefile))})
+  let status = term_getstatus(buf)
+  call assert_equal('running', status)
+  call assert_true(filereadable(donefile))
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

From 2ee25ba41be465f36e4b67bf45f75d6563754d39 Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Mon, 20 Apr 2026 09:31:22 +0800
Subject: [PATCH 2/2] vim-patch:9.2.0364: tests:
 test_smoothscroll_textoff_showbreak() fails

Problem:  tests: test_smoothscroll_textoff_showbreak() fails
          (after v9.2.0363)
Solution: Add missing CheckRunVimInTerminal

related: vim/vim#20011

https://github.com/vim/vim/commit/618a327ce6f6c7a47bdbf2a4f5d1c329d97e6037

Co-authored-by: Christian Brabandt <cb@256bit.org>
---
 test/old/testdir/test_scroll_opt.vim | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/old/testdir/test_scroll_opt.vim b/test/old/testdir/test_scroll_opt.vim
index 7c65afa38b..e5e5067b54 100644
--- a/test/old/testdir/test_scroll_opt.vim
+++ b/test/old/testdir/test_scroll_opt.vim
@@ -1448,6 +1448,7 @@ endfunc
 " not crash.
 func Test_smoothscroll_textoff_showbreak()
   CheckOption smoothscroll
+  CheckRunVimInTerminal
 
   let donefile = 'XTest_crash_textoff_showbreak_done'
   defer delete(donefile)