feat(api): add err field to nvim_echo() opts

Problem:  We want to deprecate `nvim_err_write(ln)()` but there is no
          obvious replacement (from Lua). Meanwhile we already have
          `nvim_echo()` with an `opts` argument.
Solution: Add `err` argument to `nvim_echo()` that directly maps to
          `:echoerr`.

runtime/doc/api.txt

@@ -662,6 +662,8 @@ nvim_echo({chunks}, {history}, {opts})                           *nvim_echo()*
                    `hl_group` element can be omitted for no highlight.
       • {history}  if true, add to |message-history|.
       • {opts}     Optional parameters.
+                   • err: Treat the message like |:echoerr|. Omitted `hlgroup`
+                     uses |hl-ErrorMsg| instead.
                    • verbose: Message is printed as a result of 'verbose'
                      option. If Nvim was invoked with -V3log_file, the message
                      will be redirected to the log_file and suppressed from

runtime/doc/news.txt

@@ -178,6 +178,8 @@ API
 
 • Improved API "meta" docstrings and :help documentation.
 • |nvim__ns_set()| can set properties for a namespace
+• |nvim_echo()| `err` field to print error messages and `chunks` accepts
+  highlight group IDs.
 
 DEFAULTS
 

runtime/lua/vim/_meta/api.lua

@@ -1104,6 +1104,8 @@ function vim.api.nvim_del_var(name) end
 --- `hl_group` element can be omitted for no highlight.
 --- @param history boolean if true, add to `message-history`.
 --- @param opts vim.api.keyset.echo_opts Optional parameters.
+--- - err: Treat the message like `:echoerr`. Omitted `hlgroup`
+---   uses `hl-ErrorMsg` instead.
 --- - verbose: Message is printed as a result of 'verbose' option.
 ---   If Nvim was invoked with -V3log_file, the message will be
 ---   redirected to the log_file and suppressed from direct output.

runtime/lua/vim/_meta/api_keysets.lua

@@ -88,6 +88,7 @@ error('Cannot require a meta file')
 --- @field pattern? string|string[]
 
 --- @class vim.api.keyset.echo_opts
+--- @field err? boolean
 --- @field verbose? boolean
 
 --- @class vim.api.keyset.empty

src/nvim/api/keysets_defs.h

@@ -325,6 +325,7 @@ typedef struct {
 } Dict(cmd_opts);
 
 typedef struct {
+  Boolean err;
   Boolean verbose;
 } Dict(echo_opts);
 

src/nvim/api/private/helpers.c

@@ -776,7 +776,7 @@ char *api_typename(ObjectType t)
   UNREACHABLE;
 }
 
-HlMessage parse_hl_msg(Array chunks, Error *err)
+HlMessage parse_hl_msg(Array chunks, bool is_err, Error *err)
 {
   HlMessage hl_msg = KV_INITIAL_VALUE;
   for (size_t i = 0; i < chunks.size; i++) {
@@ -791,7 +791,7 @@ HlMessage parse_hl_msg(Array chunks, Error *err)
 
     String str = copy_string(chunk.items[0].data.string, NULL);
 
-    int hl_id = 0;
+    int hl_id = is_err ? HLF_E : 0;
     if (chunk.size == 2) {
       hl_id = object_to_hl_id(chunk.items[1], "text highlight", err);
     }

src/nvim/api/vim.c

@@ -775,13 +775,15 @@ void nvim_set_vvar(String name, Object value, Error *err)
 ///                `hl_group` element can be omitted for no highlight.
 /// @param history  if true, add to |message-history|.
 /// @param opts  Optional parameters.
+///          - err: Treat the message like |:echoerr|. Omitted `hlgroup`
+///            uses |hl-ErrorMsg| instead.
 ///          - verbose: Message is printed as a result of 'verbose' option.
 ///            If Nvim was invoked with -V3log_file, the message will be
 ///            redirected to the log_file and suppressed from direct output.
 void nvim_echo(Array chunks, Boolean history, Dict(echo_opts) *opts, Error *err)
   FUNC_API_SINCE(7)
 {
-  HlMessage hl_msg = parse_hl_msg(chunks, err);
+  HlMessage hl_msg = parse_hl_msg(chunks, opts->err, err);
   if (ERROR_SET(err)) {
     goto error;
   }
@@ -790,7 +792,7 @@ void nvim_echo(Array chunks, Boolean history, Dict(echo_opts) *opts, Error *err)
     verbose_enter();
   }
 
-  msg_multihl(hl_msg, history ? "echomsg" : "echo", history);
+  msg_multihl(hl_msg, opts->err ? "echoerr" : history ? "echomsg" : "echo", history, opts->err);
 
   if (opts->verbose) {
     verbose_leave();

src/nvim/eval.c

@@ -7968,8 +7968,7 @@ void ex_execute(exarg_T *eap)
     } else if (eap->cmdidx == CMD_echoerr) {
       // We don't want to abort following commands, restore did_emsg.
       int save_did_emsg = did_emsg;
-      msg_ext_set_kind("echoerr");
-      emsg_multiline(ga.ga_data, true);
+      emsg_multiline(ga.ga_data, "echoerr", HLF_E, true);
       if (!force_abort) {
         did_emsg = save_did_emsg;
       }

src/nvim/ex_docmd.c

@@ -982,7 +982,7 @@ void handle_did_throw(void)
   if (messages != NULL) {
     do {
       msglist_T *next = messages->next;
-      emsg_multiline(messages->msg, messages->multiline);
+      emsg_multiline(messages->msg, "emsg", HLF_E, messages->multiline);
       xfree(messages->msg);
       xfree(messages->sfile);
       xfree(messages);

src/nvim/lua/executor.c

@@ -958,7 +958,7 @@ static void nlua_print_event(void **argv)
   HlMessage msg = KV_INITIAL_VALUE;
   HlMessageChunk chunk = { { .data = argv[0], .size = (size_t)(intptr_t)argv[1] - 1 }, 0 };
   kv_push(msg, chunk);
-  msg_multihl(msg, "lua_print", true);
+  msg_multihl(msg, "lua_print", true, false);
 }
 
 /// Print as a Vim message

src/nvim/message.c

@@ -293,20 +293,31 @@ void msg_multiline(String str, int hl_id, bool check_int, bool hist, bool *need_
   }
 }
 
-void msg_multihl(HlMessage hl_msg, const char *kind, bool history)
+// Avoid starting a new message for each chunk and adding message to history in msg_keep().
+static bool is_multihl = false;
+
+void msg_multihl(HlMessage hl_msg, const char *kind, bool history, bool err)
 {
   no_wait_return++;
   msg_start();
   msg_clr_eos();
   bool need_clear = false;
+  msg_ext_history = history;
   msg_ext_set_kind(kind);
+  is_multihl = true;
   for (uint32_t i = 0; i < kv_size(hl_msg); i++) {
     HlMessageChunk chunk = kv_A(hl_msg, i);
-    msg_multiline(chunk.text, chunk.hl_id, true, false, &need_clear);
+    if (err) {
+      emsg_multiline(chunk.text.data, kind, chunk.hl_id, true);
+    } else {
+      msg_multiline(chunk.text, chunk.hl_id, true, false, &need_clear);
+    }
+    assert(msg_ext_kind == kind);
   }
   if (history && kv_size(hl_msg)) {
     add_msg_hist_multihl(NULL, 0, 0, true, hl_msg);
   }
+  is_multihl = false;
   no_wait_return--;
   msg_end();
 }
@@ -342,18 +353,19 @@ bool msg_keep(const char *s, int hl_id, bool keep, bool multiline)
   }
   entered++;
 
-  // Add message to history (unless it's a repeated kept message or a
-  // truncated message)
-  if (s != keep_msg
-      || (*s != '<'
-          && last_msg_hist != NULL
-          && last_msg_hist->msg != NULL
-          && strcmp(s, last_msg_hist->msg) != 0)) {
+  // Add message to history (unless it's a truncated, repeated kept or multihl message).
+  if ((s != keep_msg
+       || (*s != '<'
+           && last_msg_hist != NULL
+           && last_msg_hist->msg != NULL
+           && strcmp(s, last_msg_hist->msg) != 0)) && !is_multihl) {
     add_msg_hist(s, -1, hl_id, multiline);
   }
 
+  if (!is_multihl) {
+    msg_start();
+  }
   // Truncate the message if needed.
-  msg_start();
   char *buf = msg_strtrunc(s, false);
   if (buf != NULL) {
     s = buf;
@@ -368,7 +380,10 @@ bool msg_keep(const char *s, int hl_id, bool keep, bool multiline)
   if (need_clear) {
     msg_clr_eos();
   }
-  bool retval = msg_end();
+  bool retval = true;
+  if (!is_multihl) {
+    retval = msg_end();
+  }
 
   if (keep && retval && vim_strsize(s) < (Rows - cmdline_row - 1) * Columns + sc_col) {
     set_keep_msg(s, 0);
@@ -618,6 +633,9 @@ void msg_source(int hl_id)
     msg_scroll = true;  // this will take more than one line
     msg(p, hl_id);
     xfree(p);
+    if (is_multihl) {
+      msg_start();  // avoided in msg_keep() but need the "msg_didout" newline here
+    }
   }
   p = get_emsg_lnum();
   if (p != NULL) {
@@ -652,7 +670,7 @@ int emsg_not_now(void)
   return false;
 }
 
-bool emsg_multiline(const char *s, bool multiline)
+bool emsg_multiline(const char *s, const char *kind, int hl_id, bool multiline)
 {
   bool ignore = false;
 
@@ -750,14 +768,13 @@ bool emsg_multiline(const char *s, bool multiline)
   }
 
   emsg_on_display = true;     // remember there is an error message
-  int hl_id = HLF_E;      // set highlight mode for error messages
   if (msg_scrolled != 0) {
     need_wait_return = true;  // needed in case emsg() is called after
   }                           // wait_return() has reset need_wait_return
                               // and a redraw is expected because
                               // msg_scrolled is non-zero
   if (msg_ext_kind == NULL) {
-    msg_ext_set_kind("emsg");
+    msg_ext_set_kind(kind);
   }
 
   // Display name and line number for the source of the error.
@@ -765,7 +782,7 @@ bool emsg_multiline(const char *s, bool multiline)
   msg_source(hl_id);
 
   if (msg_ext_kind == NULL) {
-    msg_ext_set_kind("emsg");
+    msg_ext_set_kind(kind);
   }
 
   // Display the error message itself.
@@ -781,7 +798,7 @@ bool emsg_multiline(const char *s, bool multiline)
 /// @return true if wait_return() not called
 bool emsg(const char *s)
 {
-  return emsg_multiline(s, false);
+  return emsg_multiline(s, "emsg", HLF_E, false);
 }
 
 void emsg_invreg(int name)
@@ -821,7 +838,7 @@ bool semsg_multiline(const char *const fmt, ...)
   vim_vsnprintf(errbuf, sizeof(errbuf), fmt, ap);
   va_end(ap);
 
-  ret = emsg_multiline(errbuf, true);
+  ret = emsg_multiline(errbuf, "emsg", HLF_E, true);
 
   return ret;
 }
@@ -905,7 +922,7 @@ void msg_schedule_semsg(const char *const fmt, ...)
 static void msg_semsg_multiline_event(void **argv)
 {
   char *s = argv[0];
-  emsg_multiline(s, true);
+  emsg_multiline(s, "emsg", HLF_E, true);
   xfree(s);
 }
 
@@ -1196,7 +1213,7 @@ void ex_messages(exarg_T *eap)
     msg_hist_off = true;
     for (; p != NULL && !got_int; p = p->next) {
       if (kv_size(p->multihl)) {
-        msg_multihl(p->multihl, p->kind, false);
+        msg_multihl(p->multihl, p->kind, false, false);
       } else if (p->msg != NULL) {
         msg_keep(p->msg, p->hl_id, false, p->multiline);
       }

test/functional/api/vim_spec.lua

@@ -3680,6 +3680,30 @@ describe('API', function()
       async_meths.nvim_echo({ { 'msg\nmsg' }, { 'msg' } }, false, {})
       eq('', exec_capture('messages'))
     end)
+
+    it('can print error message', function()
+      async_meths.nvim_echo({ { 'Error\nMessage' } }, false, { err = true })
+      screen:expect([[
+                                                |
+        {1:~                                       }|*3
+        {3:                                        }|
+        {9:Error}                                   |
+        {9:Message}                                 |
+        {6:Press ENTER or type command to continue}^ |
+      ]])
+      feed(':messages<CR>')
+      screen:expect([[
+        ^                                        |
+        {1:~                                       }|*6
+                                                |
+      ]])
+      async_meths.nvim_echo({ { 'Error' }, { 'Message', 'Special' } }, false, { err = true })
+      screen:expect([[
+        ^                                        |
+        {1:~                                       }|*6
+        {9:Error}{16:Message}                            |
+      ]])
+    end)
   end)
 
   describe('nvim_open_term', function()

test/functional/ui/messages_spec.lua

@@ -315,6 +315,21 @@ describe('ui/ext_messages', function()
     })
     feed('<Esc>')
     command('set showmode')
+
+    -- kind=echoerr for nvim_echo() err
+    feed(':call nvim_echo([["Error"], ["Message", "Special"]], 1, #{ err:1 })<CR>')
+    screen:expect({
+      cmdline = { {
+        abort = false,
+      } },
+      messages = {
+        {
+          content = { { 'Error', 9, 6 }, { 'Message', 16, 99 } },
+          history = true,
+          kind = 'echoerr',
+        },
+      },
+    })
   end)
 
   it(':echoerr', function()