patch 8.0.0254: error message of assert functions is sometimes incomplete

Problem:    When using an assert function one can either specify a message or
            get a message about what failed, not both.
Solution:   Concatenate the error with the message.

src/eval.c

@@ -9240,11 +9240,11 @@ fill_assert_error(
 
     if (opt_msg_tv->v_type != VAR_UNKNOWN)
     {
-	ga_concat(gap, tv2string(opt_msg_tv, &tofree, numbuf, 0));
+	ga_concat(gap, echo_string(opt_msg_tv, &tofree, numbuf, 0));
 	vim_free(tofree);
+	ga_concat(gap, (char_u *)": ");
     }
-    else
-    {
+
     if (atype == ASSERT_MATCH || atype == ASSERT_NOTMATCH)
 	ga_concat(gap, (char_u *)"Pattern ");
     else if (atype == ASSERT_NOTEQUAL)
@@ -9269,7 +9269,6 @@ fill_assert_error(
 	ga_concat_esc(gap, tv2string(got_tv, &tofree, numbuf, 0));
 	vim_free(tofree);
     }
-    }
 }
 
 

src/testdir/test_assert.vim

@@ -121,6 +121,12 @@ func Test_assert_inrange()
   call assert_fails('call assert_inrange(1, 1)', 'E119:')
 endfunc
 
+func Test_assert_with_msg()
+  call assert_equal('foo', 'bar', 'testing')
+  call assert_match("testing: Expected 'foo' but got 'bar'", v:errors[0])
+  call remove(v:errors, 0)
+endfunc
+
 func Test_user_is_happy()
   smile
   sleep 300m

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    254,
 /**/
     253,
 /**/