ui: fix problem with the popupmenu when rightleft is set

fixes #12032

2 files changed, 20 insertions, 0 deletions

diff --git a/src/nvim/ui_compositor.c b/src/nvim/ui_compositor.c
index e582d8f859..bc7fee7e96 100644
--- a/src/nvim/ui_compositor.c
+++ b/src/nvim/ui_compositor.c
@@ -311,6 +311,9 @@ ScreenGrid *ui_comp_mouse_focus(int row, int col)
 static void compose_line(Integer row, Integer startcol, Integer endcol,
                          LineFlags flags)
 {
+  // If rightleft is set, startcol may be -1. In such cases, the assertions
+  // will fail because no overlap is found. Adjust startcol to prevent it.
+  startcol = MAX(startcol, 0);
   // in case we start on the right half of a double-width char, we need to
   // check the left half. But skip it in output if it wasn't doublewidth.
   int skipstart = 0, skipend = 0;
diff --git a/test/functional/ui/popupmenu_spec.lua b/test/functional/ui/popupmenu_spec.lua
index c1c5d1ce2e..0ea0aecb00 100644
--- a/test/functional/ui/popupmenu_spec.lua
+++ b/test/functional/ui/popupmenu_spec.lua
@@ -9,6 +9,7 @@ local funcs = helpers.funcs
 local get_pathsep = helpers.get_pathsep
 local eq = helpers.eq
 local pcall_err = helpers.pcall_err
+local eval = helpers.eval
 
 describe('ui/ext_popupmenu', function()
   local screen
@@ -2196,4 +2197,20 @@ describe('builtin popupmenu', function()
       {2:-- INSERT --}                    |
     ]])
   end)
+
+  it('does not crash when displayed in the last column with rightleft (#12032)', function()
+    local col = 30
+    local items = {'word', 'choice', 'text', 'thing'}
+    local max_len = 0
+    for _, v in ipairs(items) do
+      max_len = max_len < #v and #v or max_len
+    end
+    screen:try_resize(col, 8)
+    command('set rightleft')
+    command('call setline(1, repeat(" ", &columns - '..max_len..'))')
+    feed('$i')
+    funcs.complete(col - max_len, items)
+    feed('<c-y>')
+    eq(2, eval('1+1'))
+  end)
 end)