fix(marks): ensure decor is removed with proper range (#32973)

Problem:  Paired mark whose end is in front of its start should not have
          its decor removed (as fixed by 72f630f9), but may still need to
          have its range redrawn.
Solution: Still call `buf_decor_remove()` but ensure it is not called with
          an inverse range when `extmark_del()` is called on an end mark.

src/nvim/extmark.c

@@ -180,11 +180,14 @@ void extmark_del(buf_T *buf, MarkTreeIter *itr, MTKey key, bool restore)
   }
 
   if (mt_decor_any(key)) {
-    // If key is an end mark it has been found first while iterating the marktree,
+    if (mt_invalid(key)) {
-    // indicating the decor is already invalid.
-    if (mt_invalid(key) || mt_end(key)) {
       decor_free(mt_decor(key));
     } else {
+      if (mt_end(key)) {
+        MTKey k = key;
+        key = key2;
+        key2 = k;
+      }
       buf_decor_remove(buf, key.pos.row, key2.pos.row, key.pos.col, mt_decor(key), true);
     }
   }

test/functional/ui/decorations_spec.lua

@@ -6393,24 +6393,19 @@ l5
 end)
 
 describe('decorations: virt_text', function()
-  local screen ---@type test.functional.ui.screen
+  local ns, screen ---@type integer, test.functional.ui.screen
 
   before_each(function()
     clear()
     screen = Screen.new(50, 10)
+    ns = api.nvim_create_namespace('test')
   end)
 
   it('avoids regression in #17638', function()
-    exec_lua[[
+    command 'set number relativenumber'
-      vim.wo.number = true
-      vim.wo.relativenumber = true
-    ]]
-
     command 'normal 4ohello'
     command 'normal aVIRTUAL'
 
-    local ns = api.nvim_create_namespace('test')
-
     api.nvim_buf_set_extmark(0, ns, 2, 0, {
       virt_text = {{"hello", "String"}},
       virt_text_win_col = 20,
@@ -6451,7 +6446,6 @@ describe('decorations: virt_text', function()
                                                         |
     ]]}
 
-    local ns = api.nvim_create_namespace('ns')
     for row = 1, 5 do
       api.nvim_buf_set_extmark(0, ns, row, 0, { id = 1, virt_text = {{'world', 'Normal'}} })
     end
@@ -6464,6 +6458,30 @@ describe('decorations: virt_text', function()
                                                         |
     ]]}
   end)
+
+  it('redraws correctly when removing mark whose end ends up in front of start', function()
+    command('normal 5ohello')
+    api.nvim_buf_set_extmark(0, ns, 2, 0, { end_col = 1, virt_text = {{'world', 'Normal'}} })
+    screen:expect([[
+                                                        |
+      hello                                             |
+      hello world                                       |
+      hello                                             |*2
+      hell^o                                             |
+      {1:~                                                 }|*3
+                                                        |
+    ]])
+    feed('3Gdd')
+    api.nvim_buf_clear_namespace(0, ns, 0, -1)
+    screen:expect([[
+                                                        |
+      hello                                             |
+      ^hello                                             |
+      hello                                             |*2
+      {1:~                                                 }|*4
+                                                        |
+    ]])
+  end)
 end)
 
 describe('decorations: window scoped', function()