patch 8.2.2893: multi-byte text in popup title shows up wrong

Problem:    Multi-byte text in popup title shows up wrong.
Solution:   Use the character width instead of the byte length. (Ralf Schandl,
            closes #8267, closes #8264)

src/message_test.c

@@ -120,6 +120,37 @@ test_trunc_string(void)
     vim_free(s);
 }
 
+/*
+ * Test trunc_string() with mbyte chars.
+ */
+    static void
+test_trunc_string_mbyte(void)
+{
+    char_u  *buf; // allocated every time to find uninit errors
+    char_u  *s;
+
+    buf = alloc(40);
+    s = vim_strsave((char_u *)"Ä text tha just fits");
+    trunc_string(s, buf, 20, 40);
+    assert(STRCMP(buf, "Ä text tha just fits") == 0);
+    vim_free(buf);
+    vim_free(s);
+
+    buf = alloc(40);
+    s = vim_strsave((char_u *)"a text ÄÖÜä nott fits");
+    trunc_string(s, buf, 20, 40);
+    assert(STRCMP(buf, "a text Ä...nott fits") == 0);
+    vim_free(buf);
+    vim_free(s);
+
+    buf = alloc(40);
+    s = vim_strsave((char_u *)"a text that not fitsÄ");
+    trunc_string(s, buf, 20, 40);
+    assert(STRCMP(buf, "a text t...not fitsÄ") == 0);
+    vim_free(buf);
+    vim_free(s);
+}
+
 /*
  * Test vim_snprintf() with a focus on checking that truncation is
  * correct when buffer is small, since it cannot be tested from
@@ -286,6 +317,7 @@ main(int argc, char **argv)
     set_option_value((char_u *)"encoding", 0, (char_u *)"utf-8", 0);
     init_chartab();
     test_trunc_string();
+    test_trunc_string_mbyte();
     test_vim_snprintf();
 
     set_option_value((char_u *)"encoding", 0, (char_u *)"latin1", 0);

src/popupwin.c

@@ -3822,18 +3822,30 @@ update_popups(void (*win_update)(win_T *wp))
 	title_wincol = wp->w_wincol + 1;
 	if (wp->w_popup_title != NULL)
 	{
-	    char_u  *title_text;
+	    title_len = (int)MB_CHARLEN(wp->w_popup_title);
 
-	    title_len = (int)STRLEN(wp->w_popup_title);
+	    // truncate the title if too long
-	    title_text = alloc(title_len + 1);
-	    trunc_string(wp->w_popup_title, title_text,
-					       total_width - 2, title_len + 1);
-	    screen_puts(title_text, wp->w_winrow, title_wincol,
-		      wp->w_popup_border[0] > 0 ? border_attr[0] : popup_attr);
-	    vim_free(title_text);
 	    if (title_len > total_width - 2)
+	    {
+		int	title_byte_len = (int)STRLEN(wp->w_popup_title);
+		char_u  *title_text = alloc(title_byte_len + 1);
+
+		if (title_text != NULL)
+		{
+		    trunc_string(wp->w_popup_title, title_text,
+					  total_width - 2, title_byte_len + 1);
+		    screen_puts(title_text, wp->w_winrow, title_wincol,
+				  wp->w_popup_border[0] > 0
+						? border_attr[0] : popup_attr);
+		    vim_free(title_text);
+		}
+
 		title_len = total_width - 2;
 	    }
+	    else
+		screen_puts(wp->w_popup_title, wp->w_winrow, title_wincol,
+		      wp->w_popup_border[0] > 0 ? border_attr[0] : popup_attr);
+	}
 
 	wincol = wp->w_wincol - wp->w_popup_leftoff;
 	top_padding = wp->w_popup_padding[0];

src/testdir/dumps/Test_popupwin_multibytetitle.dump

@@ -0,0 +1,10 @@
+>1+0&#ffffff0| @73
+|2| @73
+|3| @73
+|4| @25|╔+0#0000001#ffd7ff255|▶|Ä|Ö|Ü|◀|═@12|╗| +0#0000000#ffffff0@27
+|5| @25|║+0#0000001#ffd7ff255| |T+0&#e0e0e08|h|i|s| |i|s| |a| |l|i|n|e| @1| +0&#ffd7ff255|║| +0#0000000#ffffff0@27
+|6| @25|║+0#0000001#ffd7ff255| |a|n|d| |a|n|o|t|h|e|r| |l|i|n|e| |║| +0#0000000#ffffff0@27
+|7| @25|╚+0#0000001#ffd7ff255|═@17|╝| +0#0000000#ffffff0@27
+|8| @73
+|9| @73
+@57|1|,|1| @10|T|o|p| 

src/testdir/test_popupwin.vim

@@ -1799,6 +1799,11 @@ func Test_popup_title()
   call term_sendkeys(buf, ":\<CR>")
   call VerifyScreenDump(buf, 'Test_popupwin_longtitle_4', {})
 
+  call term_sendkeys(buf, ":call popup_clear()\<CR>")
+  call term_sendkeys(buf, ":call popup_menu(['This is a line', 'and another line'], #{title: '▶ÄÖÜ◀', })\<CR>")
+  call VerifyScreenDump(buf, 'Test_popupwin_multibytetitle', {})
+  call term_sendkeys(buf, "x")
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestPopupTitle')

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2893,
 /**/
     2892,
 /**/