From 89ea47f702af5abed19c8bf1826b866048772b74 Mon Sep 17 00:00:00 2001
From: Pasi Kallinen <paxed@alt.org>
Date: Sat, 15 Jun 2024 18:44:25 +0300
Subject: [PATCH] Monsters can track hero through fixed teleport traps

Also make fixed teleport traps always trigger when entered.
---
 include/extern.h |  1 +
 include/trap.h   |  2 ++
 src/mon.c        |  5 ++++-
 src/teleport.c   |  1 +
 src/track.c      | 13 +++++++++++++
 src/trap.c       | 10 ++++++++++
 6 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/extern.h b/include/extern.h
index b746f6d6b..5391be599 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -3144,6 +3144,7 @@ extern int tt_doppel(struct monst *) NONNULLARG1;
 extern void initrack(void);
 extern void settrack(void);
 extern coord *gettrack(coordxy, coordxy);
+extern boolean hastrack(coordxy, coordxy);
 extern void save_track(NHFILE *) NONNULLARG1;
 extern void rest_track(NHFILE *) NONNULLARG1;
 
diff --git a/include/trap.h b/include/trap.h
index abfb0833f..0d786b550 100644
--- a/include/trap.h
+++ b/include/trap.h
@@ -122,5 +122,7 @@ enum trap_immunities {
                                || (ttyp) == POLY_TRAP)
 /* "transportation" traps */
 #define is_xport(ttyp) ((ttyp) >= TELEP_TRAP && (ttyp) <= MAGIC_PORTAL)
+#define fixed_tele_trap(t) ((t)->ttyp == TELEP_TRAP \
+                            && isok((t)->teledest.x,(t)->teledest.x))
 
 #endif /* TRAP_H */
diff --git a/src/mon.c b/src/mon.c
index 8ccc581a8..a436dc897 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -2316,7 +2316,10 @@ mfndpos(
                                    ttmp->ttyp);
                             continue;
                     }
-                    if (!m_harmless_trap(mon, ttmp)) {
+                    /* fixed-destination teleport trap, was used by hero */
+                    if (fixed_tele_trap(ttmp) && hastrack(nx, ny))
+                        info[cnt] |= ALLOW_TRAPS;
+                    else if (!m_harmless_trap(mon, ttmp)) {
                         if (!(flag & ALLOW_TRAPS)) {
                             if (mon_knows_traps(mon, ttmp->ttyp))
                                 continue;
diff --git a/src/teleport.c b/src/teleport.c
index e50fb79aa..51fb281e7 100644
--- a/src/teleport.c
+++ b/src/teleport.c
@@ -1456,6 +1456,7 @@ tele_trap(struct trap *trap)
         coord cc;
         struct monst *mtmp = m_at(trap->teledest.x, trap->teledest.y);
 
+        settrack();
         if (mtmp) {
             if (!enexto(&cc, mtmp->mx, mtmp->my, mtmp->data)) {
                 /* could not find some other place to put mtmp; the level must
diff --git a/src/track.c b/src/track.c
index a04855c63..92a172a3b 100644
--- a/src/track.c
+++ b/src/track.c
@@ -52,6 +52,19 @@ gettrack(coordxy x, coordxy y)
     return (coord *) 0;
 }
 
+/* return TRUE if x,y has hero tracks on it */
+boolean
+hastrack(coordxy x, coordxy y)
+{
+    int i;
+
+    for (i = 0; i < utcnt; i++)
+        if (utrack[i].x == x && utrack[i].y == y)
+            return TRUE;
+
+    return FALSE;
+}
+
 /* save the hero tracking info */
 void
 save_track(NHFILE *nhfp)
diff --git a/src/trap.c b/src/trap.c
index ab99adf5e..301d686ae 100644
--- a/src/trap.c
+++ b/src/trap.c
@@ -2897,6 +2897,11 @@ dotrap(struct trap *trap, unsigned trflags)
 
     nomul(0);
 
+    if (fixed_tele_trap(trap)) {
+        trflags |= FORCETRAP;
+        forcetrap = TRUE;
+    }
+
     /* KMH -- You can't escape the Sokoban level traps */
     if (Sokoban && (is_pit(ttype) || is_hole(ttype))) {
         /* The "air currents" message is still appropriate -- even when
@@ -3654,6 +3659,11 @@ mintrap(struct monst *mtmp, unsigned mintrapflags)
         boolean already_seen = (mon_knows_traps(mtmp, tt)
                                 || (tt == HOLE && !mindless(mptr)));
 
+        if (fixed_tele_trap(trap)) {
+            mintrapflags |= FORCETRAP;
+            forcetrap = TRUE;
+        }
+
         if (mtmp == u.usteed) {
             ; /* true when called from dotrap, inescapable is not an option */
         } else if (Sokoban && (is_pit(tt) || is_hole(tt)) && !trap->madeby_u) {