grep -Fo could report a match that is not the longest

* src/kwset.c (acexec): Fix it.
* tests/fgrep-longest: New test.
* tests/Makefile.am: Add the test.
* NEWS: Mention it.

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/fgrep-longest b/tests/fgrep-longest
new file mode 100755
index 00000000..5974d113
--- /dev/null
+++ b/tests/fgrep-longest
@@ -0,0 +1,23 @@
+#! /bin/sh
+# With multiple matches, grep -Fo could print a shorter one.
+# This bug affected grep versions 2.26 through 2.27.
+#
+# Copyright (C) 2017 Free Software Foundation, Inc.
+#
+# Copying and distribution of this file, with or without modification,
+# are permitted in any medium without royalty provided the copyright
+# notice and this notice are preserved.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+
+fail=0
+
+# The erroneous versions would print "c", rather than the longer match, "bce".
+printf 'abce\n' > in || framework_failure_
+printf 'abcd\nc\nbce\n' > pat || framework_failure_
+printf 'bce\n' > exp || framework_failure_
+
+LC_ALL=C grep -Fof pat in > out || fail=1
+compare exp out || fail=1
+
+Exit $fail