re2: feed unicode string to re2 module when necessary

My previous test were using the `pyre2` Python project, that wrap the Google RE2 library
in python as a `re2` module and accept bytes as input. However the `fb-re2`
Python project is also offering a wrapping of the Google RE2 library in python
as a `re2` module ans accept only unicode on python3. So we detect this
situation and convert thing to unicode when necessary.

Hooray…

We should consider using a rust wrapping for regexp handling. We needs regexps
in Rust anyway and this give use more control with less variants and more
sanity.

Differential Revision: https://phab.mercurial-scm.org/D10284

mercurial/util.py

@@ -2157,6 +2157,7 b' def fscasesensitive(path):'
         return True
 
 
+_re2_input = lambda x: x
 try:
     import re2  # pytype: disable=import-error
 
@@ -2168,11 +2169,21 b' except ImportError:'
 class _re(object):
     def _checkre2(self):
         global _re2
+        global _re2_input
         try:
             # check if match works, see issue3964
-            _re2 = bool(re2.match(br'\[([^\[]+)\]', b'[ui]'))
+            check_pattern = br'\[([^\[]+)\]'
+            check_input = b'[ui]'
+            _re2 = bool(re2.match(check_pattern, check_input))
         except ImportError:
             _re2 = False
+        except TypeError:
+            # the `pyre-2` project provides a re2 module that accept bytes
+            # the `fb-re2` project provides a re2 module that acccept sysstr
+            check_pattern = pycompat.sysstr(check_pattern)
+            check_input = pycompat.sysstr(check_input)
+            _re2 = bool(re2.match(check_pattern, check_input))
+            _re2_input = pycompat.sysstr
 
     def compile(self, pat, flags=0):
         """Compile a regular expression, using re2 if possible
@@ -2188,7 +2199,7 b' class _re(object):'
             if flags & remod.MULTILINE:
                 pat = b'(?m)' + pat
             try:
-                return re2.compile(pat)
+                return re2.compile(_re2_input(pat))
             except re2.error:
                 pass
         return remod.compile(pat, flags)