sl0ppty: say what the config could not honour

A config that half-applied said nothing. An unknown shader, a binding
that does not parse, an include that is not there: the file loaded, that
line did not, and the session announced "config reloaded" as though
nothing had happened. Every one of those messages was already being
produced -- config_load has filled `err` on a successful load since it
was written -- and then dropped on the floor by every caller, because a
non-zero return meant "fine".

So the complaint from the last load is kept, and the front end says it
where it would have said "config reloaded". Once at startup too: a config
that loaded with a complaint still started the session, and the stderr
line goes where nobody attached can read it. The `reload` control verb
answers `{"ok":true,"warning":"..."}` -- ok, because the file did apply,
with the reason attached for a script that cares.

Two things fell out of writing the test for it.

An include's complaint was reported by nobody when the file in the middle
was fine. apply_includes only looked at the return value, so a theme that
loaded while *its* include was missing swallowed the message: the child
returned true, and true meant there was nothing to say. The complaint now
travels up whether or not the include itself loaded.

And a complaint now carries the name of the file it happened in, exactly
once -- added by the file that produced it, never by the files that
included it, because prefixing at every level builds a chain that
truncates before the part that matters. So:

    t.kdl: unknown shader: bloom
    keys.kdl: line 2: unknown action fly
    b.kdl: includes nested too deep (a cycle?)
    cannot open /home/you/.config/sl0ppty/themes/nope.kdl

which is enough to know which file to open, in a message that fits in a
toast.

1 files changed, 14 insertions, 1 deletions

diff --git a/src/cmd.c b/src/cmd.c
index 758586b..5c3792a 100644
--- a/src/cmd.c
+++ b/src/cmd.c
@@ -278,7 +278,20 @@ static char *cmd_json(app_t *a, screen_t *s, input_parser_t *in,
     }
     app_resize(a, s->cols, s->rows); /* geometry may have moved */
     s->force_full = true;
-    app_toast(a, "config reloaded");
+    /* A complaint is not a failure: the file applied and one line of it did
+     * not, so the reply is ok with a reason attached rather than an error. A
+     * script that cares can look; the session says it out loud either way. */
+    const char *why = app_config_complaint();
+    app_toast(a, why && *why ? why : "config reloaded");
+    if (why && *why) {
+      json_t j;
+      json_init(&j);
+      json_obj_open(&j, NULL);
+      json_bool(&j, "ok", true);
+      json_str(&j, "warning", why, strlen(why));
+      json_obj_close(&j);
+      return j.buf;
+    }
     return jok_int(NULL, 0);
   }
   if (strcmp(cmd, "alive") == 0) {