fix at_beginning

Lib/test/test_re.py

@@ -88,8 +88,6 @@ class ReTests(unittest.TestCase):
         int_value = int(matchobj.group(0))
         return str(int_value + 1)
 
-    # TODO: RUSTPYTHON
-    # @unittest.expectedFailure
     def test_basic_re_sub(self):
         self.assertTypedEqual(re.sub('y', 'a', 'xyz'), 'xaz')
         self.assertTypedEqual(re.sub('y', S('a'), S('xyz')), 'xaz')
@@ -1661,8 +1659,6 @@ class ReTests(unittest.TestCase):
         self.checkPatternError(r'(?i+', 'missing -, : or )', 3)
         self.checkPatternError(r'(?iz', 'unknown flag', 3)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_bug_6509(self):
         # Replacement strings of both types must parse properly.
         # all strings

extra_tests/snippets/stdlib_re.py

@@ -59,4 +59,6 @@ assert re.compile('(a)(bc)').match('abc')[1] == 'a'
 assert re.compile('a(b)(?P<a>c)d').match('abcd').groupdict() == {'a': 'c'}
 
 # test op branch
-assert re.compile(r'((?=\d|\.\d)(?P<int>\d*)|a)', re.DEBUG).match('123.2132').group() == '123'
+assert re.compile(r'((?=\d|\.\d)(?P<int>\d*)|a)').match('123.2132').group() == '123'
+
+assert re.sub(r'^\s*', 'X', 'test') == 'Xtest'

vm/src/stdlib/sre/interp.rs

@@ -274,7 +274,8 @@ trait MatchContextDrive {
         self.state().pattern_codes.len() - self.ctx().code_position
     }
     fn at_beginning(&self) -> bool {
-        self.ctx().string_position == self.state().start
+        // self.ctx().string_position == self.state().start
+        self.ctx().string_position == 0
     }
     fn at_end(&self) -> bool {
         self.ctx().string_position == self.state().end