UI: redraw statusline when entering cmdline (#8347)

src/nvim/ex_getln.c

@@ -347,6 +347,13 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
     redrawcmd();
   }
 
+  // redraw the statusline for statuslines that display the current mode
+  // using the mode() function.
+  if (KeyTyped) {
+    curwin->w_redr_status = true;
+    redraw_statuslines();
+  }
+
   did_emsg = false;
   got_int = false;
   s->state.check = command_line_check;

test/functional/ui/cmdline_spec.lua

@@ -157,6 +157,27 @@ describe('external cmdline', function()
     end)
   end)
 
+  it("redraws statusline on entering", function()
+    command('set laststatus=2')
+    command('set statusline=%{mode()}')
+    feed(':')
+    screen:expect([[
+                               |
+      {1:~                        }|
+      {1:~                        }|
+      {3:c^                        }|
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "" } },
+        firstc = ":",
+        indent = 0,
+        pos = 0,
+        prompt = ""
+      }}, cmdline)
+    end)
+  end)
+
   it("works with input()", function()
     feed(':call input("input", "default")<cr>')
     screen:expect([[