fix(messages): messages added to history missing from ext_messages "g<" #33907

Problem:  Messages that are already added to the history are not emitted
          as part of the "g<" msg_history_show event.

Solution: Move clearing the history for temporary messages to before
          adding a message to the history, rather than after emitting
          a message.

src/nvim/message.c

@@ -1031,8 +1031,15 @@ static void msg_hist_add(const char *s, int len, int hl_id)
   msg_hist_add_multihl(msg, false);
 }
 
+static bool do_clear_hist_temp = true;
+
 static void msg_hist_add_multihl(HlMessage msg, bool temp)
 {
+  if (do_clear_hist_temp) {
+    msg_hist_clear_temp();
+    do_clear_hist_temp = false;
+  }
+
   if (msg_hist_off || msg_silent != 0) {
     hl_msg_free(msg);
     return;
@@ -2207,8 +2214,6 @@ static void msg_ext_emit_chunk(void)
   ADD(*msg_ext_chunks, ARRAY_OBJ(chunk));
 }
 
-static bool do_clear_hist_temp = true;
-
 /// The display part of msg_puts_len().
 /// May be called recursively to display scroll-back text.
 static void msg_puts_display(const char *str, int maxlen, int hl_id, int recurse)
@@ -2237,10 +2242,6 @@ static void msg_puts_display(const char *str, int maxlen, int hl_id, int recurse
     int col = (int)(maxlen < 0 ? mb_string2cells(p) : mb_string2cells_len(p, (size_t)(maxlen)));
     msg_col = (lastline ? 0 : msg_col) + col;
 
-    if (do_clear_hist_temp && !strequal(msg_ext_kind, "return_prompt")) {
-      msg_hist_clear_temp();
-      do_clear_hist_temp = false;
-    }
     return;
   }
 
@@ -2696,6 +2697,7 @@ void show_sb_text(void)
 {
   if (ui_has(kUIMessages)) {
     exarg_T ea = { .arg = "", .skip = true };
+    msg_ext_clear(true);
     ex_messages(&ea);
     return;
   }

test/functional/ui/messages_spec.lua

@@ -1638,7 +1638,7 @@ stack traceback:
         },
       },
     })
-    feed(':messages<CR>g<lt>')
+    feed('g<lt>')
     screen:expect({
       grid = [[
         ^                         |
@@ -1662,6 +1662,40 @@ stack traceback:
         },
       },
     })
+    feed('Q')
+    screen:expect({
+      grid = [[
+        ^                         |
+        {1:~                        }|*4
+      ]],
+      messages = {
+        {
+          content = { { "E354: Invalid register name: '^@'", 9, 6 } },
+          history = true,
+          kind = 'emsg',
+        },
+      },
+    })
+    feed('g<lt>')
+    screen:expect({
+      grid = [[
+        ^                         |
+        {1:~                        }|*4
+      ]],
+      messages = {
+        {
+          content = { { 'Press ENTER or type command to continue', 6, 18 } },
+          history = false,
+          kind = 'return_prompt',
+        },
+      },
+      msg_history = {
+        {
+          content = { { "E354: Invalid register name: '^@'", 9, 6 } },
+          kind = 'emsg',
+        },
+      },
+    })
   end)
 
   it('single event for multiple :set options', function()