prevent infinite recursion in impossible

doc/fixes34.3

@@ -100,6 +100,7 @@ prevent "see it drop from your pack" when figurine monster becomes undetected
 attempting to drop a subset of a stack of multiple cursed loadstones could
 	corrupt inventory or cause a crash
 "miss" message was missing for thrown or kicked gold not caught by a monster
+prevent recursive impossible() and panic() calls from leading to a stack overflow
 
 
 Platform- and/or Interface-Specific Fixes

include/decl.h

@@ -152,6 +152,10 @@ E NEARDATA struct sinfo {
 	int panicking;		/* `panic' is in progress */
 #if defined(VMS) || defined(WIN32)
 	int exiting;		/* an exit handler is executing */
+#endif
+	int in_impossible;
+#ifdef PANICLOG
+	int in_paniclog;
 #endif
 } program_state;
 

src/files.c

@@ -2275,12 +2275,16 @@ const char *reason;	/* explanation */
 	FILE *lfile;
 	char buf[BUFSZ];
 
-	lfile = fopen_datafile(PANICLOG, "a", TROUBLEPREFIX);
-	if (lfile) {
-	    (void) fprintf(lfile, "%s %08ld: %s %s\n",
-			   version_string(buf), yyyymmdd((time_t)0L),
-			   type, reason);
-	    (void) fclose(lfile);
+	if (!program_state.in_paniclog) {
+		program_state.in_paniclog = 1;
+		lfile = fopen_datafile(PANICLOG, "a", TROUBLEPREFIX);
+		if (lfile) {
+		    (void) fprintf(lfile, "%s %08ld: %s %s\n",
+				   version_string(buf), yyyymmdd((time_t)0L),
+				   type, reason);
+		    (void) fclose(lfile);
+		}
+		program_state.in_paniclog = 0;
 	}
 #endif /* PANICLOG */
 	return;

src/pline.c

@@ -252,6 +252,9 @@ void
 impossible VA_DECL(const char *, s)
 	VA_START(s);
 	VA_INIT(s, const char *);
+	if (program_state.in_impossible)
+		panic("impossible called impossible");
+	program_state.in_impossible = 1;
 	{
 	    char pbuf[BUFSZ];
 	    Vsprintf(pbuf,s,VA_ARGS);
@@ -259,6 +262,7 @@ impossible VA_DECL(const char *, s)
 	}
 	vpline(s,VA_ARGS);
 	pline("Program in disorder - perhaps you'd better #quit.");
+	program_state.in_impossible = 0;
 	VA_END();
 }