global: use raw strings for regular expressions with escapes
Escape sequences like \w, \s, and \d are technically invalid
in str/bytes. This became a deprecation warning in Python 3.6
(https://bugs.python.org/issue27364). Python 3.8 bumps it to
a SyntaxWarning (https://bugs.python.org/issue32912), which is
non-silent by default.
This commit changes a number of regular expressions to use
br'' so regular expression special sequences don't need \\
literals. This fixes roughly half of the SyntaxWarning we
see in the code base with Python 3.8.
Differential Revision: https://phab.mercurial-scm.org/D5815
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present