regex: work around a bug in glibc-2.27 and prior

* m4/regex.m4 (gl_REGEX): Reject any system regexp that gets a failed
assertion for /0|()0|\1|0/.
* tests/test-regex.c (main): Add the same test here.

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/test-regex.c b/tests/test-regex.c
index 0a009b896c..a0aa1123be 100644
--- a/tests/test-regex.c
+++ b/tests/test-regex.c
@@ -237,6 +237,17 @@ main (void)
   if (! REG_STARTEND)
     result |= 64;
 
+  /* Matching with the compiled form of this regexp would provoke
+     an assertion failure prior to glibc-2.28:
+       regexec.c:1375: pop_fail_stack: Assertion 'num >= 0' failed
+     With glibc-2.28, compilation fails and reports the invalid
+     back reference.  */
+  re_set_syntax (RE_SYNTAX_POSIX_EGREP);
+  memset (&regex, 0, sizeof regex);
+  s = re_compile_pattern ("0|()0|\\1|0", 10, &regex);
+  if (!s || strcmp (s, "Invalid back reference"))
+    result |= 64;
+
 #if 0
   /* It would be nice to reject hosts whose regoff_t values are too
      narrow (including glibc on hosts with 64-bit ptrdiff_t and