From 6dc99f69b79d3639c078458a4018aba4f3ec7e2b Mon Sep 17 00:00:00 2001
From: Pasi Kallinen <paxed@alt.org>
Date: Sun, 22 Aug 2021 18:44:17 +0300
Subject: [PATCH] Prevent impossible trying to find a door position

When random dungeon level generation looks for room walls
to place doors at (for joining corridors or creating niches),
it complained about impossible, if the shaped theme room
doesn't have a valid place for a door.

Make the position routine return FALSE and let the
caller deal with it...

Observed this with the small circular themeroom which had
all 4 valid positions already joined with corridors, and
the niche function tried to add a niche to the room.
---
 src/mklev.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/src/mklev.c b/src/mklev.c
index 6b4aab52b..b25e0e58a 100644
--- a/src/mklev.c
+++ b/src/mklev.c
@@ -34,7 +34,7 @@ static void do_room_or_subroom(struct mkroom *, int, int, int, int, boolean,
                                schar, boolean, boolean);
 static void makerooms(void);
 static boolean door_into_nonjoined(xchar, xchar);
-static void finddpos(coord *, xchar, xchar, xchar, xchar);
+static boolean finddpos(coord *, xchar, xchar, xchar, xchar);
 static void mkinvpos(xchar, xchar, int);
 static void mk_knox_portal(xchar, xchar);
 
@@ -90,7 +90,7 @@ door_into_nonjoined(xchar x, xchar y)
     return FALSE;
 }
 
-static void
+static boolean
 finddpos(coord *cc, xchar xl, xchar yl, xchar xh, xchar yh)
 {
     register xchar x, y;
@@ -112,12 +112,11 @@ finddpos(coord *cc, xchar xl, xchar yl, xchar xh, xchar yh)
     /* cannot find something reasonable -- strange */
     x = xl;
     y = yh;
-    impossible("finddpos: couldn't find door pos within (%d,%d,%d,%d)",
-               xl, yl, xh, yh);
+    return FALSE;
  gotit:
     cc->x = x;
     cc->y = y;
-    return;
+    return TRUE;
 }
 
 /* Sort rooms on the level so they're ordered from left to right on the map.
@@ -347,29 +346,37 @@ join(register int a, register int b, boolean nxcor)
         dy = 0;
         xx = croom->hx + 1;
         tx = troom->lx - 1;
-        finddpos(&cc, xx, croom->ly, xx, croom->hy);
-        finddpos(&tt, tx, troom->ly, tx, troom->hy);
+        if (!finddpos(&cc, xx, croom->ly, xx, croom->hy))
+            return;
+        if (!finddpos(&tt, tx, troom->ly, tx, troom->hy))
+            return;
     } else if (troom->hy < croom->ly) {
         dy = -1;
         dx = 0;
         yy = croom->ly - 1;
-        finddpos(&cc, croom->lx, yy, croom->hx, yy);
         ty = troom->hy + 1;
-        finddpos(&tt, troom->lx, ty, troom->hx, ty);
+        if (!finddpos(&cc, croom->lx, yy, croom->hx, yy))
+            return;
+        if (!finddpos(&tt, troom->lx, ty, troom->hx, ty))
+            return;
     } else if (troom->hx < croom->lx) {
         dx = -1;
         dy = 0;
         xx = croom->lx - 1;
         tx = troom->hx + 1;
-        finddpos(&cc, xx, croom->ly, xx, croom->hy);
-        finddpos(&tt, tx, troom->ly, tx, troom->hy);
+        if (!finddpos(&cc, xx, croom->ly, xx, croom->hy))
+            return;
+        if (!finddpos(&tt, tx, troom->ly, tx, troom->hy))
+            return;
     } else {
         dy = 1;
         dx = 0;
         yy = croom->hy + 1;
         ty = troom->ly - 1;
-        finddpos(&cc, croom->lx, yy, croom->hx, yy);
-        finddpos(&tt, troom->lx, ty, troom->hx, ty);
+        if (!finddpos(&cc, croom->lx, yy, croom->hx, yy))
+            return;
+        if (!finddpos(&tt, troom->lx, ty, troom->hx, ty))
+            return;
     }
     xx = cc.x;
     yy = cc.y;
@@ -541,10 +548,12 @@ place_niche(register struct mkroom *aroom, int *dy, int *xx, int *yy)
 
     if (rn2(2)) {
         *dy = 1;
-        finddpos(&dd, aroom->lx, aroom->hy + 1, aroom->hx, aroom->hy + 1);
+        if (!finddpos(&dd, aroom->lx, aroom->hy + 1, aroom->hx, aroom->hy + 1))
+            return FALSE;
     } else {
         *dy = -1;
-        finddpos(&dd, aroom->lx, aroom->ly - 1, aroom->hx, aroom->ly - 1);
+        if (!finddpos(&dd, aroom->lx, aroom->ly - 1, aroom->hx, aroom->ly - 1))
+            return FALSE;
     }
     *xx = dd.x;
     *yy = dd.y;