sh: Successfully do nothing when killing a terminated job.

If a job has terminated but is still known, silently do nothing when using
the kill builtin with the job specifier. Formerly, the shell called kill()
with the process group ID that might have been reused.

bin/kill/kill.c

@@ -133,9 +133,15 @@ main(int argc, char *argv[])
 
 	for (errors = 0; argc; argc--, argv++) {
 #ifdef SHELL
-		if (**argv == '%')
+		if (**argv == '%') {
 			pid = getjobpgrp(*argv);
-		else
+			/*
+			 * Silently ignore terminated jobs, like the kernel
+			 * silently ignores zombies.
+			 */
+			if (pid == 0)
+				continue;
+		} else
 #endif
 		{
 			pid = strtol(*argv, &ep, 10);

bin/sh/jobs.c

@@ -645,6 +645,8 @@ getjobpgrp(char *name)
 	struct job *jp;
 
 	jp = getjob(name);
+	if (jp->state == JOBDONE)
+		return 0;
 	return -jp->ps[0].pid;
 }
 

bin/sh/tests/builtins/Makefile

@@ -86,6 +86,7 @@ FILES+=		hash3.0 hash3.0.stdout
 FILES+=		hash4.0
 FILES+=		jobid1.0
 FILES+=		jobid2.0
+FILES+=		kill1.0
 FILES+=		lineno.0 lineno.0.stdout
 FILES+=		lineno2.0
 FILES+=		local1.0

bin/sh/tests/builtins/kill1.0

@@ -0,0 +1,8 @@
+# $FreeBSD$
+
+: &
+p1=$!
+: &
+p2=$!
+wait $p2
+kill %1