Don't skip forking for an external command if any traps are active.

Example:
  sh -c '(trap "echo trapped" EXIT; sleep 3)'
now correctly prints "trapped".

With this check, it is no longer necessary to check for -T
explicitly in that case.

This is a useful bugfix by itself and also important because I plan to
skip forking more often.

PR:		bin/113860 (part of)
PR:		bin/74404 (part of)
Reviewed by:	stefanf
Approved by:	ed (mentor)

bin/sh/eval.c

@@ -731,7 +731,7 @@ evalcommand(union node *cmd, int flags, struct backcmd *backcmd)
 	/* Fork off a child process if necessary. */
 	if (cmd->ncmd.backgnd
 	 || (cmdentry.cmdtype == CMDNORMAL
-	    && ((flags & EV_EXIT) == 0 || Tflag))
+	    && ((flags & EV_EXIT) == 0 || have_traps()))
 	 || ((flags & EV_BACKCMD) != 0
 	    && (cmdentry.cmdtype != CMDBUILTIN
 		 || cmdentry.u.index == CDCMD

bin/sh/trap.c

@@ -221,6 +221,21 @@ clear_traps(void)
 }
 
 
+/*
+ * Check if we have any traps enabled.
+ */
+int
+have_traps(void)
+{
+	char *volatile *tp;
+
+	for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
+		if (*tp && **tp)	/* trap not NULL or SIG_IGN */
+			return 1;
+	}
+	return 0;
+}
+
 /*
  * Set the signal handler for the specified signal.  The routine figures
  * out what it should be set to.

bin/sh/trap.h

@@ -39,6 +39,7 @@ extern volatile sig_atomic_t gotwinch;
 
 int trapcmd(int, char **);
 void clear_traps(void);
+int have_traps(void);
 void setsignal(int);
 void ignoresig(int);
 void onsig(int);