fix(f_wait): flush UI before blocking (#25962)

src/nvim/eval/funcs.c

@@ -2911,6 +2911,9 @@ static void f_wait(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
   bool error = false;
   const int called_emsg_before = called_emsg;
 
+  // Flush screen updates before blocking.
+  ui_flush();
+
   LOOP_PROCESS_EVENTS_UNTIL(&main_loop, main_loop.events, timeout,
                             eval_expr_typval(&expr, false, &argv, 0, &exprval) != OK
                             || tv_get_number_chk(&exprval, &error)

src/nvim/getchar.c

@@ -1723,7 +1723,7 @@ static void getchar_common(typval_T *argvars, typval_T *rettv)
       // getchar(): blocking wait.
       // TODO(bfredl): deduplicate shared logic with state_enter ?
       if (!char_avail()) {
-        // flush output before waiting
+        // Flush screen updates before blocking.
         ui_flush();
         (void)os_inchar(NULL, 0, -1, typebuf.tb_change_cnt, main_loop.events);
         if (!multiqueue_empty(main_loop.events)) {

src/nvim/lua/executor.c

@@ -463,7 +463,7 @@ static int nlua_wait(lua_State *lstate)
   int pcall_status = 0;
   bool callback_result = false;
 
-  // Flush UI before blocking
+  // Flush screen updates before blocking.
   ui_flush();
 
   LOOP_PROCESS_EVENTS_UNTIL(&main_loop,

src/nvim/state.c

@@ -70,7 +70,7 @@ getkey:
         update_screen();
         setcursor();  // put cursor back where it belongs
       }
-      // Flush screen updates before blocking
+      // Flush screen updates before blocking.
       ui_flush();
       // Call `os_inchar` directly to block for events or user input without
       // consuming anything from `input_buffer`(os/input.c) or calling the

test/functional/core/job_spec.lua

@@ -875,25 +875,41 @@ describe('jobs', function()
       end)
     end)
 
-    it('hides cursor when waiting', function()
-      local screen = Screen.new(30, 3)
+    it('hides cursor and flushes messages before blocking', function()
+      local screen = Screen.new(50, 6)
       screen:set_default_attr_ids({
-        [0] = {foreground = Screen.colors.Blue1, bold = true};
+        [0] = {foreground = Screen.colors.Blue, bold = true};  -- NonText
+        [1] = {bold = true, reverse = true};  -- MsgSeparator
+        [2] = {bold = true, foreground = Screen.colors.SeaGreen};  -- MoreMsg
       })
       screen:attach()
       command([[let g:id = jobstart([v:progpath, '--clean', '--headless'])]])
-      feed_command('call jobwait([g:id], 300)')
+      source([[
+        func PrintAndWait()
+          echon "aaa\nbbb"
+          call jobwait([g:id], 300)
+          echon "\nccc"
+        endfunc
+      ]])
+      feed_command('call PrintAndWait()')
       screen:expect{grid=[[
-                                      |
-        {0:~                             }|
-        :call jobwait([g:id], 300)    |
+                                                          |
+        {0:~                                                 }|
+        {0:~                                                 }|
+        {1:                                                  }|
+        aaa                                               |
+        bbb                                               |
       ]], timeout=100}
-      funcs.jobstop(meths.get_var('id'))
       screen:expect{grid=[[
-        ^                              |
-        {0:~                             }|
-        :call jobwait([g:id], 300)    |
+                                                          |
+        {1:                                                  }|
+        aaa                                               |
+        bbb                                               |
+        ccc                                               |
+        {2:Press ENTER or type command to continue}^           |
       ]]}
+      feed('<CR>')
+      funcs.jobstop(meths.get_var('id'))
     end)
   end)
 

test/functional/lua/vim_spec.lua

@@ -2559,7 +2559,6 @@ describe('lua stdlib', function()
       ]])
     end)
 
-
     it('should not block other events', function()
       eq({time = true, wait_result = true}, exec_lua[[
         start_time = get_time()
@@ -2601,6 +2600,7 @@ describe('lua stdlib', function()
         }
       ]])
     end)
+
     it('should work with vim.defer_fn', function()
       eq({time = true, wait_result = true}, exec_lua[[
         start_time = get_time()

test/functional/ui/messages_spec.lua

@@ -1312,17 +1312,54 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
     ]])
   end)
 
-  it('echo messages are shown correctly when getchar() immediately follows', function()
-    feed([[:echo 'foo' | echo 'bar' | call getchar()<CR>]])
-    screen:expect([[
-                                                                  |
-      {1:~                                                           }|
-      {1:~                                                           }|
-      {1:~                                                           }|
-      {3:                                                            }|
-      foo                                                         |
-      bar^                                                         |
-    ]])
+  describe('echo messages are shown when immediately followed by', function()
+    --- @param to_block  string           command to cause a blocking wait
+    --- @param to_unblock  number|string  number: timeout for blocking screen
+    ---                                   string: keys to stop the blocking wait
+    local function test_flush_before_block(to_block, to_unblock)
+      local timeout = type(to_unblock) == 'number' and to_unblock or nil
+      exec(([[
+        func PrintAndWait()
+          echon "aaa\nbbb"
+          %s
+          echon "\nccc"
+        endfunc
+      ]]):format(to_block))
+      feed(':call PrintAndWait()<CR>')
+      screen:expect{grid=[[
+                                                                    |
+        {1:~                                                           }|
+        {1:~                                                           }|
+        {1:~                                                           }|
+        {3:                                                            }|
+        aaa                                                         |
+        bbb^                                                         |
+      ]], timeout=timeout}
+      if type(to_unblock) == 'string' then
+        feed(to_unblock)
+      end
+      screen:expect{grid=[[
+                                                                    |
+        {1:~                                                           }|
+        {3:                                                            }|
+        aaa                                                         |
+        bbb                                                         |
+        ccc                                                         |
+        {4:Press ENTER or type command to continue}^                     |
+      ]]}
+    end
+
+    it('getchar()', function()
+      test_flush_before_block([[call getchar()]], 'k')
+    end)
+
+    it('wait()', function()
+      test_flush_before_block([[call wait(300, '0')]], 100)
+    end)
+
+    it('lua vim.wait()', function()
+      test_flush_before_block([[lua vim.wait(300, function() end)]], 100)
+    end)
   end)
 
   it('consecutive calls to win_move_statusline() work after multiline message #21014',function()