A clua monster method for finding its summoner

The crawl UI highlights a monster's summoner in LOS examination mode,
but there was previously no way to determine a monster's summoner from
clua. This commit adds a summoner_pos() method to the monster info table
that returns a pair of LOS coordinates of the monster's summoner. It
returns nil if the monster's isn't summoned or it the monster or its
summoner are not in LOS. I've copied the summoning monster's mid into
the monster_info class and updated the examination mode UI to use this
information. This way we have a centralized check for whether the
summoner is valid to reveal, at least regardless of LOS concerns.

crawl-ref/source/directn.cc

@@ -2020,15 +2020,11 @@ void direction_chooser::do_redraws()
 
 coord_def direction_chooser::find_summoner()
 {
-    const monster* mon = monster_at(target());
-
-    if (mon && mon->is_summoned()
-        // Don't leak information about rakshasa mirrored illusions.
-        && !mon->has_ench(ENCH_PHANTOM_MIRROR)
-        // Don't leak information about invisible or out-of-los summons.
-        && you.can_see(*mon))
+    const auto *mon = monster_at(target());
+    if (mon && mon->is_summoned() && you.can_see(*mon))
     {
-        const monster *summ = monster_by_mid(mon->summoner);
+        monster_info mi(mon);
+        const monster *summ = monster_by_mid(mi.summoner_id);
         // Don't leak information about invisible summoners.
         if (summ && you.can_see(*summ))
             return summ->pos();
@@ -2039,8 +2035,7 @@ coord_def direction_chooser::find_summoner()
 void direction_chooser::highlight_summoner(crawl_view_buffer &vbuf)
 {
     const coord_def summ_loc = find_summoner();
-
-    if (summ_loc == INVALID_COORD || !you.see_cell(summ_loc))
+    if (summ_loc == INVALID_COORD)
         return;
 
     auto& cell = vbuf(grid2view(summ_loc) - 1);

crawl-ref/source/l-moninf.cc

@@ -841,6 +841,32 @@ LUAFN(moninf_get_name)
     return 1;
 }
 
+/*
+ * The x,y coordinates of the monster that summoned this monster, in player
+ * centered coordinates. If the monster was not summoned by another monster
+ * that's currently in LOS, return nil.
+ * @treturn int
+ * @treturn int
+ * @function pos
+ */
+LUAFN(moninf_get_summoner_pos)
+{
+    MONINF(ls, 1, mi);
+
+    const auto *summoner = monster_by_mid(mi->summoner_id);
+    if (summoner && you.can_see(*summoner))
+    {
+        lua_pushnumber(ls, summoner->pos().x - you.pos().x);
+        lua_pushnumber(ls, summoner->pos().y - you.pos().y);
+        return 2;
+    }
+    else
+    {
+        lua_pushnil(ls);
+        return 1;
+    }
+}
+
 static const struct luaL_reg moninf_lib[] =
 {
     MIREG(type),
@@ -895,6 +921,7 @@ static const struct luaL_reg moninf_lib[] =
     MIREG(x_pos),
     MIREG(y_pos),
     MIREG(pos),
+    MIREG(summoner_pos),
     MIREG(avg_local_depth),
     MIREG(avg_local_prob),
 

crawl-ref/source/mon-info.cc

@@ -391,7 +391,8 @@ monster_info::monster_info(monster_type p_type, monster_type p_base_type)
             props[MUTANT_BEAST_FACETS].get_vector().push_back(i);
     }
 
-    client_id = 0;
+    client_id = MID_NOBODY;
+    summoner_id = MID_NOBODY;
 }
 
 static description_level_type _article_for(const actor* a)
@@ -448,17 +449,22 @@ monster_info::monster_info(const monster* m, int milev)
 
     _colour = m->colour;
 
+    summoner_id = MID_NOBODY;
     if (m->is_summoned()
         && !(m->flags & MF_PERSISTS)
         && (!m->has_ench(ENCH_PHANTOM_MIRROR) || m->friendly()))
     {
         mb.set(MB_SUMMONED);
+
         if (m->is_abjurable())
             mb.set(MB_ABJURABLE);
         else
             mb.set(MB_MINION);
+
         if (m->type == MONS_SPELLFORGED_SERVITOR && m->summoner == MID_PLAYER)
             mb.set(MB_PLAYER_SERVITOR);
+
+        summoner_id = m->summoner;
     }
     else if ((m->is_unrewarding()
                  || testbits(m->flags, MF_NO_REWARD)

crawl-ref/source/mon-info.h

@@ -296,7 +296,8 @@ struct monster_info_base
     bool umbraed;
     int shield_bonus;
 
-    uint32_t client_id;
+    mid_t client_id;
+    mid_t summoner_id;
 };
 
 // Monster info used by the pane; precomputes some data