fix(messages): list_cmd kind for :registers, :au[g] #32531

Problem:  No kind for `:registers/autocmd/augroup` messages. `:registers`
          chunks are emitted as separate `msg_show` events.

Solution: Add the `list_cmd` kind to the message. Introduce a new
          `msg_ext_skip_flush` variable to set to true around a
          group of to be paired message chunks.

4 files changed, 13 insertions, 4 deletions

diff --git a/src/nvim/autocmd.c b/src/nvim/autocmd.c
index ad27823667..34ad734528 100644
--- a/src/nvim/autocmd.c
+++ b/src/nvim/autocmd.c
@@ -554,6 +554,7 @@ void do_augroup(char *arg, bool del_group)
     current_augroup = augroup_add(arg);
   } else {  // ":aug": list the group names
     msg_start();
+    msg_ext_set_kind("list_cmd");
 
     String name;
     int value;
@@ -855,6 +856,7 @@ void do_autocmd(exarg_T *eap, char *arg_in, int forceit)
   // Print header when showing autocommands.
   if (is_showing) {
     // Highlight title
+    msg_ext_set_kind("list_cmd");
     msg_puts_title(_("\n--- Autocommands ---"));
 
     if (*arg == '*' || *arg == '|' || *arg == NUL) {
diff --git a/src/nvim/message.c b/src/nvim/message.c
index 6fc102e4ff..ef4cde8a80 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -3162,6 +3162,8 @@ void msg_ext_ui_flush(void)
   if (!ui_has(kUIMessages)) {
     msg_ext_kind = NULL;
     return;
+  } else if (msg_ext_skip_flush) {
+    return;
   }
 
   msg_ext_emit_chunk();
diff --git a/src/nvim/message.h b/src/nvim/message.h
index 13746406f9..55c58114f4 100644
--- a/src/nvim/message.h
+++ b/src/nvim/message.h
@@ -34,6 +34,8 @@ extern MessageHistoryEntry *first_msg_hist;
 extern MessageHistoryEntry *last_msg_hist;
 
 EXTERN bool msg_ext_need_clear INIT( = false);
+// Set to true to force grouping a set of message chunks into a single `cmdline_show` event.
+EXTERN bool msg_ext_skip_flush INIT( = false);
 
 /// allocated grid for messages. Used when display+=msgsep is set, or
 /// ext_multigrid is active. See also the description at msg_scroll_flush()
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index 2491621fbc..6c437bcb2c 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -3770,10 +3770,16 @@ void ex_display(exarg_T *eap)
   }
   int hl_id = HLF_8;
 
+  msg_ext_set_kind("list_cmd");
+  msg_ext_skip_flush = true;
   // Highlight title
   msg_puts_title(_("\nType Name Content"));
   for (int i = -1; i < NUM_REGISTERS && !got_int; i++) {
     int name = get_register_name(i);
+    if (arg != NULL && vim_strchr(arg, name) == NULL) {
+      continue;             // did not ask for this register
+    }
+
     switch (get_reg_type(name, NULL)) {
     case kMTLineWise:
       type = 'l'; break;
@@ -3783,10 +3789,6 @@ void ex_display(exarg_T *eap)
       type = 'b'; break;
     }
 
-    if (arg != NULL && vim_strchr(arg, name) == NULL) {
-      continue;             // did not ask for this register
-    }
-
     if (i == -1) {
       if (y_previous != NULL) {
         yb = y_previous;
@@ -3890,6 +3892,7 @@ void ex_display(exarg_T *eap)
     msg_puts("\n  c  \"=   ");
     dis_msg(expr_line, false);
   }
+  msg_ext_skip_flush = false;
 }
 
 /// display a string for do_dis()