fix(messages): list_cmd kind for buffer line messages (#33855)

Problem:  Missing kind and separate event for each line for message
          containing buffer lines for e.g. `:print`.
Solution: Set the `list_cmd` kind and only `msg_start()` for the first
          message, print a newline instead.

src/nvim/ex_cmds.c

@@ -1470,7 +1470,7 @@ void append_redir(char *const buf, const size_t buflen, const char *const opt,
   }
 }
 
-void print_line_no_prefix(linenr_T lnum, int use_number, bool list)
+void print_line_no_prefix(linenr_T lnum, bool use_number, bool list)
 {
   char numbuf[30];
 
@@ -1483,7 +1483,7 @@ void print_line_no_prefix(linenr_T lnum, int use_number, bool list)
 }
 
 /// Print a text line.  Also in silent mode ("ex -s").
-void print_line(linenr_T lnum, int use_number, bool list)
+void print_line(linenr_T lnum, bool use_number, bool list, bool first)
 {
   bool save_silent = silent_mode;
 
@@ -1492,12 +1492,17 @@ void print_line(linenr_T lnum, int use_number, bool list)
     return;
   }
 
-  msg_start();
   silent_mode = false;
   info_message = true;  // use stdout, not stderr
+  if (first) {
+    msg_start();
+    msg_ext_set_kind("list_cmd");
+  } else if (!save_silent) {
+    msg_putchar('\n');  // don't want trailing newline with regular messaging
+  }
   print_line_no_prefix(lnum, use_number, list);
   if (save_silent) {
-    msg_putchar('\n');
+    msg_putchar('\n');  // batch mode message should always end in newline
     silent_mode = save_silent;
   }
   info_message = false;
@@ -3039,7 +3044,7 @@ void ex_z(exarg_T *eap)
       }
     }
 
-    print_line(i, eap->flags & EXFLAG_NR, eap->flags & EXFLAG_LIST);
+    print_line(i, eap->flags & EXFLAG_NR, eap->flags & EXFLAG_LIST, i == start);
 
     if (minus && i == lnum) {
       msg_putchar('\n');
@@ -4259,7 +4264,7 @@ skip:
       global_need_beginline = true;
     }
     if (subflags.do_print) {
-      print_line(curwin->w_cursor.lnum, subflags.do_number, subflags.do_list);
+      print_line(curwin->w_cursor.lnum, subflags.do_number, subflags.do_list, true);
     }
   } else if (!global_busy) {
     if (got_int) {

src/nvim/ex_docmd.c

@@ -5129,14 +5129,13 @@ static void ex_print(exarg_T *eap)
   if (curbuf->b_ml.ml_flags & ML_EMPTY) {
     emsg(_(e_empty_buffer));
   } else {
-    for (; !got_int; os_breakcheck()) {
-      print_line(eap->line1,
+    for (linenr_T line = eap->line1; line <= eap->line2 && !got_int; os_breakcheck()) {
+      print_line(line,
                  (eap->cmdidx == CMD_number || eap->cmdidx == CMD_pound
                   || (eap->flags & EXFLAG_NR)),
-                 eap->cmdidx == CMD_list || (eap->flags & EXFLAG_LIST));
-      if (++eap->line1 > eap->line2) {
-        break;
-      }
+                 eap->cmdidx == CMD_list || (eap->flags & EXFLAG_LIST),
+                 line == eap->line1);
+      line++;
     }
     setpcmark();
     // put cursor at last line
@@ -6360,7 +6359,7 @@ void ex_may_print(exarg_T *eap)
 {
   if (eap->flags != 0) {
     print_line(curwin->w_cursor.lnum, (eap->flags & EXFLAG_NR),
-               (eap->flags & EXFLAG_LIST));
+               (eap->flags & EXFLAG_LIST), true);
     ex_no_reprint = true;
   }
 }

test/functional/ui/messages_spec.lua

@@ -522,6 +522,23 @@ describe('ui/ext_messages', function()
         },
       },
     })
+
+    feed(':1,2p<CR>')
+    screen:expect({
+      grid = [[
+        line 1                   |
+        ^line                     |
+        {1:~                        }|*3
+      ]],
+      cmdline = { { abort = false } },
+      messages = {
+        {
+          content = { { 'line 1\nline ' } },
+          history = false,
+          kind = 'list_cmd',
+        },
+      },
+    })
   end)
 
   it(':echoerr', function()