Show immunity when targetting an MR-resistible spell (#9391).

Pain on a zombie, for example, will show "not susceptible" rather than an
irrelevant percentage.

As mentioned in comments, this is implemented with an ultra-wrong hack, but
the alternative seems to be massive code duplication. This relates back to
fundamental issues with the place of monster_info in the codebase, which
are beyond the scope of this commit.

crawl-ref/source/ability.cc

@@ -2601,7 +2601,8 @@ static spret_type _do_ability(const ability_def& abil, bool fail)
         direction_chooser_args args;
         args.mode = TARG_HOSTILE;
         args.get_desc_func = bind(desc_success_chance, placeholders::_1,
-                                  zap_ench_power(ZAP_BANISHMENT, pow), false);
+                                  zap_ench_power(ZAP_BANISHMENT, pow), false,
+                                  nullptr);
         if (!spell_direction(spd, beam, &args))
             return SPRET_ABORT;
 

crawl-ref/source/beam.cc

@@ -4115,7 +4115,7 @@ void bolt::update_hurt_or_helped(monster* mon)
     {
         if (nasty_to(mon))
             foe_info.hurt++;
-        else if (nice_to(mon))
+        else if (nice_to(monster_info(mon)))
         {
             foe_info.helped++;
             // Accidentally helped a foe.
@@ -4137,7 +4137,7 @@ void bolt::update_hurt_or_helped(monster* mon)
             if (!is_tracer && mon->mid == source_id)
                 xom_is_stimulated(100);
         }
-        else if (nice_to(mon))
+        else if (nice_to(monster_info(mon)))
             friend_info.helped++;
     }
 }
@@ -6285,7 +6285,7 @@ bool bolt::nasty_to(const monster* mon) const
         return false;
 
     // Positive effects.
-    if (nice_to(mon))
+    if (nice_to(monster_info(mon)))
         return false;
 
     // Co-aligned inner flame is fine.
@@ -6328,14 +6328,14 @@ bool bolt::nasty_to(const monster* mon) const
 // Return true if the bolt is considered nice by mon.
 // This is not the inverse of nasty_to(): the bolt needs to be
 // actively positive.
-bool bolt::nice_to(const monster* mon) const
+bool bolt::nice_to(const monster_info& mi) const
 {
     // Polymorphing a (very) ugly thing will mutate it into a different
     // (very) ugly thing.
     if (flavour == BEAM_POLYMORPH)
     {
-        return mon->type == MONS_UGLY_THING
-               || mon->type == MONS_VERY_UGLY_THING;
+        return mi.type == MONS_UGLY_THING
+               || mi.type == MONS_VERY_UGLY_THING;
     }
 
     if (flavour == BEAM_HASTE
@@ -6348,7 +6348,7 @@ bool bolt::nice_to(const monster* mon) const
         return true;
     }
 
-    if (flavour == BEAM_GHOSTLY_FLAME && mon->holiness() & MH_UNDEAD)
+    if (flavour == BEAM_GHOSTLY_FLAME && mi.holi & MH_UNDEAD)
         return true;
 
     return false;

crawl-ref/source/beam.h

@@ -186,7 +186,7 @@ struct bolt
     bool god_cares() const; // Will the god be unforgiving about this beam?
     bool is_harmless(const monster* mon) const;
     bool nasty_to(const monster* mon) const;
-    bool nice_to(const monster* mon) const;
+    bool nice_to(const monster_info& mi) const;
     bool has_saving_throw() const;
 
     void draw(const coord_def& p);

crawl-ref/source/directn.cc

@@ -2355,7 +2355,7 @@ static bool _find_mlist(const coord_def& where, int idx, bool need_path,
 static bool _want_target_monster(const monster *mon, targ_mode_type mode,
                                  targetter* hitfunc)
 {
-    if (hitfunc && !hitfunc->affects_monster(*mon))
+    if (hitfunc && !hitfunc->affects_monster(monster_info(mon)))
         return false;
     switch (mode)
     {

crawl-ref/source/evoke.cc

@@ -619,7 +619,8 @@ void zap_wand(int slot)
                              SPFLAG_MR_CHECK))
     {
         args.get_desc_func = bind(desc_success_chance, placeholders::_1,
-                                  zap_ench_power(type_zapped, power), true);
+                                  zap_ench_power(type_zapped, power), true,
+                                  hitfunc);
     }
     direction(zap_wand, args);
 

crawl-ref/source/spl-cast.cc

@@ -1211,12 +1211,15 @@ int hex_success_chance(const int mr, int powc, int scale, bool round_up)
 }
 
 // Include success chance in targeter for spells checking monster MR.
-vector<string> desc_success_chance(const monster_info& mi, int pow, bool evoked)
+vector<string> desc_success_chance(const monster_info& mi, int pow, bool evoked,
+                                   targetter* hitfunc)
 {
     vector<string> descs;
     const int mr = mi.res_magic();
     if (mr == MAG_IMMUNE)
         descs.push_back("magic immune");
+    else if (hitfunc && !hitfunc->affects_monster(mi))
+        descs.push_back("not susceptible");
     else
     {
         int success = hex_success_chance(mr,
@@ -1314,7 +1317,7 @@ spret_type your_spells(spell_type spell, int powc,
             const int eff_pow = zap == NUM_ZAPS ? powc
                                                 : zap_ench_power(zap, powc);
             additional_desc = bind(desc_success_chance, placeholders::_1,
-                                   eff_pow, evoked);
+                                   eff_pow, evoked, hitfunc.get());
         }
 
         string title = "Aiming: <white>";

crawl-ref/source/spl-cast.h

@@ -97,7 +97,9 @@ void do_cast_spell_cmd(bool force);
 
 int hex_success_chance(const int mr, int powc, int scale,
                        bool round_up = false);
-vector<string> desc_success_chance(const monster_info& mi, int pow, bool evoked);
+class targetter;
+vector<string> desc_success_chance(const monster_info& mi, int pow, bool evoked,
+                                   targetter* hitfunc);
 spret_type your_spells(spell_type spell, int powc = 0, bool allow_fail = true,
     bool evoked = false, bool fake_spell = false);
 

crawl-ref/source/target.cc

@@ -61,7 +61,7 @@ bool targetter::has_additional_sites(coord_def loc)
     return false;
 }
 
-bool targetter::affects_monster(const monster& mon)
+bool targetter::affects_monster(const monster_info& mon)
 {
     return true; //TODO: false
 }
@@ -226,11 +226,15 @@ aff_type targetter_beam::is_affected(coord_def loc)
                               AFF_MULTIPLE;
 }
 
-bool targetter_beam::affects_monster(const monster& mon)
+bool targetter_beam::affects_monster(const monster_info& mon)
 {
-    return !beam.is_harmless(&mon) || beam.nice_to(&mon)
+    //XXX: this is a disgusting hack that probably leaks information!
+    //     bolt::is_harmless (and transitively, bolt::nasty_to) should
+    //     take monster_infos instead.
+    const monster* m = monster_at(mon.pos);
+    return m && (!beam.is_harmless(m) || beam.nice_to(mon))
            && !(beam.has_saving_throw() && beam.flavour != BEAM_VIRULENCE
-                && mons_immune_magic(&mon));
+                && mon.res_magic() == MAG_IMMUNE);
 }
 
 targetter_unravelling::targetter_unravelling(const actor *act, int r, int pow)

crawl-ref/source/target.h

@@ -32,7 +32,7 @@ class targetter
 
     virtual aff_type is_affected(coord_def loc) = 0;
     virtual bool has_additional_sites(coord_def a);
-    virtual bool affects_monster(const monster& mon);
+    virtual bool affects_monster(const monster_info& mon);
 protected:
     bool anyone_there(coord_def loc);
 };
@@ -47,7 +47,7 @@ class targetter_beam : public targetter
     bool valid_aim(coord_def a) override;
     bool can_affect_outside_range() override;
     virtual aff_type is_affected(coord_def loc) override;
-    virtual bool affects_monster(const monster& mon) override;
+    virtual bool affects_monster(const monster_info& mon) override;
 protected:
     vector<coord_def> path_taken; // Path beam took.
     void set_explosion_aim(bolt tempbeam);