fix(messages): proper multiline Lua print() messages #31205

Problem:  Separate message emitted for each newline present in Lua
          print() arguments.
Solution: Make msg_multiline() handle NUL bytes. Refactor print() to use
          msg_multiline(). Refactor vim.print() to use print().

src/nvim/eval.c

@@ -7881,7 +7881,7 @@ void ex_echo(exarg_T *eap)
       char *tofree = encode_tv2echo(&rettv, NULL);
       if (*tofree != NUL) {
         msg_ext_set_kind("echo");
-        msg_multiline(tofree, echo_hl_id, true, false, &need_clear);
+        msg_multiline(cstr_as_string(tofree), echo_hl_id, true, false, &need_clear);
       }
       xfree(tofree);
     }

src/nvim/ex_cmds.c

@@ -189,7 +189,7 @@ void do_ascii(exarg_T *eap)
                    transchar(c), buf1, buf2, cval, cval, cval);
     }
 
-    msg_multiline(IObuff, 0, true, false, &need_clear);
+    msg_multiline(cstr_as_string(IObuff), 0, true, false, &need_clear);
 
     off += (size_t)utf_ptr2len(data);  // needed for overlong ascii?
   }
@@ -224,7 +224,7 @@ void do_ascii(exarg_T *eap)
                    c, c, c);
     }
 
-    msg_multiline(IObuff, 0, true, false, &need_clear);
+    msg_multiline(cstr_as_string(IObuff), 0, true, false, &need_clear);
 
     off += (size_t)utf_ptr2len(data + off);  // needed for overlong ascii?
   }

src/nvim/lua/executor.c

@@ -954,41 +954,10 @@ static void nlua_common_free_all_mem(lua_State *lstate)
 
 static void nlua_print_event(void **argv)
 {
-  char *str = argv[0];
-  const size_t len = (size_t)(intptr_t)argv[1] - 1;  // exclude final NUL
-
-  for (size_t i = 0; i < len;) {
-    if (got_int) {
-      break;
-    }
-    const size_t start = i;
-    while (i < len) {
-      switch (str[i]) {
-      case NUL:
-        str[i] = NL;
-        i++;
-        continue;
-      case NL:
-        // TODO(bfredl): use proper multiline msg? Probably should implement
-        // print() in lua in terms of nvim_message(), when it is available.
-        str[i] = NUL;
-        i++;
-        break;
-      default:
-        i++;
-        continue;
-      }
-      break;
-    }
-    msg(str + start, 0);
-    if (msg_silent == 0) {
-      msg_didout = true;  // Make blank lines work properly
-    }
-  }
-  if (len && str[len - 1] == NUL) {  // Last was newline
-    msg("", 0);
-  }
-  xfree(str);
+  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);
 }
 
 /// Print as a Vim message

src/nvim/message.c

@@ -249,35 +249,33 @@ bool msg(const char *s, const int hl_id)
   return msg_hl_keep(s, hl_id, false, false);
 }
 
-/// Similar to msg_outtrans, but support newlines and tabs.
-void msg_multiline(const char *s, int hl_id, bool check_int, bool hist, bool *need_clear)
+/// Similar to msg_outtrans_len, but support newlines and tabs.
+void msg_multiline(String str, int hl_id, bool check_int, bool hist, bool *need_clear)
   FUNC_ATTR_NONNULL_ALL
 {
-  const char *next_spec = s;
-
-  while (next_spec != NULL) {
+  const char *s = str.data;
+  const char *chunk = s;
+  while ((size_t)(s - str.data) < str.size) {
     if (check_int && got_int) {
       return;
     }
-    next_spec = strpbrk(s, "\t\n\r");
+    if (*s == '\n' || *s == TAB || *s == '\r') {
+      // Print all chars before the delimiter
+      msg_outtrans_len(chunk, (int)(s - chunk), hl_id, hist);
 
-    if (next_spec != NULL) {
-      // Printing all char that are before the char found by strpbrk
-      msg_outtrans_len(s, (int)(next_spec - s), hl_id, hist);
-
-      if (*next_spec != TAB && *need_clear) {
+      if (*s != TAB && *need_clear) {
         msg_clr_eos();
         *need_clear = false;
       }
-      msg_putchar_hl((uint8_t)(*next_spec), hl_id);
-      s = next_spec + 1;
+      msg_putchar_hl((uint8_t)(*s), hl_id);
+      chunk = s + 1;
     }
+    s++;
   }
 
-  // Print the rest of the message. We know there is no special
-  // character because strpbrk returned NULL
-  if (*s != NUL) {
-    msg_outtrans(s, hl_id, hist);
+  // Print the rest of the message
+  if (*chunk != NUL) {
+    msg_outtrans_len(chunk, (int)(str.size - (size_t)(chunk - str.data)), hl_id, hist);
   }
 }
 
@@ -290,7 +288,7 @@ void msg_multihl(HlMessage hl_msg, const char *kind, bool history)
   msg_ext_set_kind(kind);
   for (uint32_t i = 0; i < kv_size(hl_msg); i++) {
     HlMessageChunk chunk = kv_A(hl_msg, i);
-    msg_multiline(chunk.text.data, chunk.hl_id, true, false, &need_clear);
+    msg_multiline(chunk.text, chunk.hl_id, true, false, &need_clear);
   }
   if (history && kv_size(hl_msg)) {
     add_msg_hist_multihl(NULL, 0, 0, true, hl_msg);
@@ -349,7 +347,7 @@ bool msg_hl_keep(const char *s, int hl_id, bool keep, bool multiline)
 
   bool need_clear = true;
   if (multiline) {
-    msg_multiline(s, hl_id, false, false, &need_clear);
+    msg_multiline(cstr_as_string(s), hl_id, false, false, &need_clear);
   } else {
     msg_outtrans(s, hl_id, false);
   }
@@ -2689,12 +2687,13 @@ static void msg_puts_printf(const char *str, const ptrdiff_t maxlen)
     // primitive way to compute the current column
     if (*s == '\r' || *s == '\n') {
       msg_col = 0;
+      msg_didout = false;
     } else {
       msg_col += cw;
+      msg_didout = true;
     }
     s += len;
   }
-  msg_didout = true;  // assume that line is not empty
 }
 
 /// Show the more-prompt and handle the user response.