sh: Ignore error when cd writes the directory actually switched to.

If CDPATH is used non-trivially or the operand is "-", cd writes the
directory actually switched to. (We currently do this only in interactive
shells, but POSIX requires this in non-interactive shells as well.)

As mentioned in Austin group bug #1045, cd shall not return an error while
leaving the current directory changed. Therefore, ignore any write error.

bin/sh/cd.c

@@ -164,8 +164,17 @@ docd(char *dest, int print, int phys)
 	if ((phys || (rc = cdlogical(dest)) < 0) && (rc = cdphysical(dest)) < 0)
 		return (-1);
 
-	if (print && iflag && curdir)
+	if (print && iflag && curdir) {
 		out1fmt("%s\n", curdir);
+		/*
+		 * Ignore write errors to preserve the invariant that the
+		 * current directory is changed iff the exit status is 0
+		 * (or 1 if -e was given and the full pathname could not be
+		 * determined).
+		 */
+		flushout(out1);
+		outclearerror(out1);
+	}
 
 	return (rc);
 }

bin/sh/sh.1

@@ -2018,6 +2018,11 @@ to return exit status 1 if the full pathname of the new directory
 cannot be determined reliably or at all.
 Normally this is not considered an error,
 although a warning is printed.
+.Pp
+If changing the directory fails, the exit status is greater than 1.
+If the directory is changed, the exit status is 0, or also 1 if
+.Fl e
+was given.
 .It Ic chdir
 A synonym for the
 .Ic cd

bin/sh/tests/builtins/Makefile

@@ -51,6 +51,7 @@ ${PACKAGE}FILES+=		cd6.0
 ${PACKAGE}FILES+=		cd7.0
 ${PACKAGE}FILES+=		cd8.0
 ${PACKAGE}FILES+=		cd9.0 cd9.0.stdout
+${PACKAGE}FILES+=		cd10.0
 ${PACKAGE}FILES+=		command1.0
 ${PACKAGE}FILES+=		command2.0
 ${PACKAGE}FILES+=		command3.0

bin/sh/tests/builtins/cd10.0

@@ -0,0 +1,6 @@
+# $FreeBSD$
+
+# Precondition
+(cd /bin) || exit
+# Verify write error is ignored.
+$SH +m -ic 'CDPATH=/:; cd bin 1</dev/null'