feat(messages): add :!cmd shell message kinds

Also print stderr error messages with ErrorMsg highlight group.

runtime/doc/news.txt

@@ -96,7 +96,7 @@ EVENTS
   • `msg_show`:
     • `history` argument indicating if the message was added to the history.
     • new message kinds: "bufwrite", "completion", "list_cmd", "lua_print",
-      "search_cmd", "undo", "verbose", wildlist".
+      "search_cmd", "shell_out/err/ret", "undo", "verbose", wildlist".
 
 HIGHLIGHTS
 

runtime/doc/ui.txt

@@ -805,6 +805,9 @@ must handle.
 		"quickfix"	Quickfix navigation message
 		"search_cmd"	Entered search command
 		"search_count"	Search count message ("S" flag of 'shortmess')
+		"shell_err"	|:!cmd| shell stderr output
+		"shell_out"	|:!cmd| shell stdout output
+		"shell_ret"	|:!cmd| shell return code
 		"undo"		|:undo| and |:redo| message
 		"verbose"	'verbose' message
 		"wildlist"	'wildmode' "list" message

src/nvim/event/proc.h

@@ -21,8 +21,8 @@ static inline Proc proc_init(Loop *loop, ProcType type, void *data)
     .argv = NULL,
     .exepath = NULL,
     .in = { .closed = false },
-    .out = { .s.closed = false },
-    .err = { .s.closed = false },
+    .out = { .s.closed = false, .s.fd = STDOUT_FILENO },
+    .err = { .s.closed = false, .s.fd = STDERR_FILENO },
     .cb = NULL,
     .closed = false,
     .internal_close_cb = NULL,

src/nvim/os/shell.c

@@ -700,6 +700,7 @@ int os_call_shell(char *cmd, int opts, char *extra_args)
   }
 
   if (!emsg_silent && exitcode != 0 && !(opts & kShellOptSilent)) {
+    msg_ext_set_kind("shell_ret");
     msg_puts(_("\nshell returned "));
     msg_outnum(exitcode);
     msg_putchar('\n');
@@ -1067,7 +1068,7 @@ static void out_data_ring(const char *output, size_t size)
   }
 
   if (output == NULL && size == SIZE_MAX) {   // Print mode
-    out_data_append_to_screen(last_skipped, &last_skipped_len, true);
+    out_data_append_to_screen(last_skipped, &last_skipped_len, STDOUT_FILENO, true);
     return;
   }
 
@@ -1095,14 +1096,15 @@ static void out_data_ring(const char *output, size_t size)
 /// @param output       Data to append to screen lines.
 /// @param count        Size of data.
 /// @param eof          If true, there will be no more data output.
-static void out_data_append_to_screen(const char *output, size_t *count, bool eof)
+static void out_data_append_to_screen(const char *output, size_t *count, int fd, bool eof)
   FUNC_ATTR_NONNULL_ALL
 {
   const char *p = output;
   const char *end = output + *count;
+  msg_ext_set_kind(fd == STDERR_FILENO ? "shell_err" : "shell_out");
   while (p < end) {
     if (*p == '\n' || *p == '\r' || *p == TAB || *p == BELL) {
-      msg_putchar_hl((uint8_t)(*p), 0);
+      msg_putchar_hl((uint8_t)(*p), fd == STDERR_FILENO ? HLF_E : 0);
       p++;
     } else {
       // Note: this is not 100% precise:
@@ -1118,7 +1120,7 @@ static void out_data_append_to_screen(const char *output, size_t *count, bool eo
         goto end;
       }
 
-      msg_outtrans_len(p, i, 0, false);
+      msg_outtrans_len(p, i, fd == STDERR_FILENO ? HLF_E : 0, false);
       p += i;
     }
   }
@@ -1133,7 +1135,7 @@ static size_t out_data_cb(RStream *stream, const char *ptr, size_t count, void *
     // Save the skipped output. If it is the final chunk, we display it later.
     out_data_ring(ptr, count);
   } else if (count > 0) {
-    out_data_append_to_screen(ptr, &count, eof);
+    out_data_append_to_screen(ptr, &count, stream->s.fd, eof);
   }
 
   return count;

test/functional/ui/messages_spec.lua

@@ -331,6 +331,7 @@ describe('ui/ext_messages', function()
       },
     })
 
+    -- kind=verbose for :verbose messages
     feed(':1verbose filter Diff[AC] hi<CR>')
     screen:expect({
       cmdline = { {
@@ -380,6 +381,43 @@ describe('ui/ext_messages', function()
         },
       },
     })
+
+    -- kind=shell for :!cmd messages
+    local cmd = t.is_os('win') and 'echo stdout& echo stderr>&2& exit 3'
+      or '{ echo stdout; echo stderr >&2; exit 3; }'
+    feed(('<CR>:!%s<CR>'):format(cmd))
+    screen:expect({
+      cmdline = { {
+        abort = false,
+      } },
+      messages = {
+        {
+          content = { { (':!%s\r\n[No write since last change]\n'):format(cmd) } },
+          history = false,
+          kind = '',
+        },
+        {
+          content = { { ('stdout%s\n'):format(t.is_os('win') and '\r' or '') } },
+          history = false,
+          kind = 'shell_out',
+        },
+        {
+          content = { { ('stderr%s\n'):format(t.is_os('win') and '\r' or ''), 9, 6 } },
+          history = false,
+          kind = 'shell_err',
+        },
+        {
+          content = { { '\nshell returned 3\n\n' } },
+          history = false,
+          kind = 'shell_ret',
+        },
+        {
+          content = { { 'Press ENTER or type command to continue', 6, 18 } },
+          history = false,
+          kind = 'return_prompt',
+        },
+      },
+    })
   end)
 
   it(':echoerr', function()