[3.6] bpo-30375: Correct the stacklevel of regex compiling warnings. (GH-1595) (#1604)

Warnings emitted when compile a regular expression now always point
to the line in the user code.  Previously they could point into inners
of the re module if emitted from inside of groups or conditionals..
(cherry picked from commit c7ac7280c321b3c1679fe5f657a6be0f86adf173)

3 files changed, 31 insertions, 15 deletions

diff --git a/Lib/sre_parse.py b/Lib/sre_parse.py
index e1c7496..608f9a2 100644
--- a/Lib/sre_parse.py
+++ b/Lib/sre_parse.py
@@ -404,7 +404,7 @@ def _escape(source, escape, state):
         pass
     raise source.error("bad escape %s" % escape, len(escape))
 
-def _parse_sub(source, state, verbose, nested=True):
+def _parse_sub(source, state, verbose, nested):
     # parse an alternation: a|b|c
 
     items = []
@@ -412,7 +412,8 @@ def _parse_sub(source, state, verbose, nested=True):
     sourcematch = source.match
     start = source.tell()
     while True:
-        itemsappend(_parse(source, state, verbose, not nested and not items))
+        itemsappend(_parse(source, state, verbose, nested + 1,
+                           not nested and not items))
         if not sourcematch("|"):
             break
 
@@ -454,10 +455,10 @@ def _parse_sub(source, state, verbose, nested=True):
     subpattern.append((BRANCH, (None, items)))
     return subpattern
 
-def _parse_sub_cond(source, state, condgroup, verbose):
-    item_yes = _parse(source, state, verbose)
+def _parse_sub_cond(source, state, condgroup, verbose, nested):
+    item_yes = _parse(source, state, verbose, nested + 1)
     if source.match("|"):
-        item_no = _parse(source, state, verbose)
+        item_no = _parse(source, state, verbose, nested + 1)
         if source.next == "|":
             raise source.error("conditional backref with more than two branches")
     else:
@@ -466,7 +467,7 @@ def _parse_sub_cond(source, state, condgroup, verbose):
     subpattern.append((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
     return subpattern
 
-def _parse(source, state, verbose, first=False):
+def _parse(source, state, verbose, nested, first=False):
     # parse a simple pattern
     subpattern = SubPattern(state)
 
@@ -692,7 +693,7 @@ def _parse(source, state, verbose, first=False):
                         lookbehindgroups = state.lookbehindgroups
                         if lookbehindgroups is None:
                             state.lookbehindgroups = state.groups
-                    p = _parse_sub(source, state, verbose)
+                    p = _parse_sub(source, state, verbose, nested + 1)
                     if dir < 0:
                         if lookbehindgroups is None:
                             state.lookbehindgroups = None
@@ -739,7 +740,7 @@ def _parse(source, state, verbose, first=False):
                                     source.string[:20],  # truncate long regexes
                                     ' (truncated)' if len(source.string) > 20 else '',
                                 ),
-                                DeprecationWarning, stacklevel=7
+                                DeprecationWarning, stacklevel=nested + 6
                             )
                         if (state.flags & SRE_FLAG_VERBOSE) and not verbose:
                             raise Verbose
@@ -757,11 +758,11 @@ def _parse(source, state, verbose, first=False):
                 except error as err:
                     raise source.error(err.msg, len(name) + 1) from None
             if condgroup:
-                p = _parse_sub_cond(source, state, condgroup, verbose)
+                p = _parse_sub_cond(source, state, condgroup, verbose, nested + 1)
             else:
                 sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and
                                not (del_flags & SRE_FLAG_VERBOSE))
-                p = _parse_sub(source, state, sub_verbose)
+                p = _parse_sub(source, state, sub_verbose, nested + 1)
             if not source.match(")"):
                 raise source.error("missing ), unterminated subpattern",
                                    source.tell() - start)
@@ -851,7 +852,7 @@ def parse(str, flags=0, pattern=None):
     pattern.str = str
 
     try:
-        p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, False)
+        p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
     except Verbose:
         # the VERBOSE flag was switched on inside the pattern.  to be
         # on the safe side, we'll parse the whole thing again...
@@ -859,7 +860,7 @@ def parse(str, flags=0, pattern=None):
         pattern.flags = flags | SRE_FLAG_VERBOSE
         pattern.str = str
         source.seek(0)
-        p = _parse_sub(source, pattern, True, False)
+        p = _parse_sub(source, pattern, True, 0)
 
     p.pattern.flags = fix_flags(str, p.pattern.flags)
 
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index c52417b..e88d0b3 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -1348,6 +1348,7 @@ class ReTests(unittest.TestCase):
             str(warns.warnings[0].message),
             'Flags not at the start of the expression %s' % p
         )
+        self.assertEqual(warns.warnings[0].filename, __file__)
 
         p = upper_char + '(?i)%s' % ('.?' * 100)
         with self.assertWarns(DeprecationWarning) as warns:
@@ -1356,6 +1357,7 @@ class ReTests(unittest.TestCase):
             str(warns.warnings[0].message),
             'Flags not at the start of the expression %s (truncated)' % p[:20]
         )
+        self.assertEqual(warns.warnings[0].filename, __file__)
 
         with self.assertWarns(DeprecationWarning):
             self.assertTrue(re.match('(?s).(?i)' + upper_char, '\n' + lower_char))
@@ -1367,14 +1369,23 @@ class ReTests(unittest.TestCase):
             self.assertTrue(re.match('^(?i)' + upper_char, lower_char))
         with self.assertWarns(DeprecationWarning):
             self.assertTrue(re.match('$|(?i)' + upper_char, lower_char))
-        with self.assertWarns(DeprecationWarning):
+        with self.assertWarns(DeprecationWarning) as warns:
             self.assertTrue(re.match('(?:(?i)' + upper_char + ')', lower_char))
-        with self.assertWarns(DeprecationWarning):
+        self.assertRegex(str(warns.warnings[0].message),
+                         'Flags not at the start')
+        self.assertEqual(warns.warnings[0].filename, __file__)
+        with self.assertWarns(DeprecationWarning) as warns:
             self.assertTrue(re.fullmatch('(^)?(?(1)(?i)' + upper_char + ')',
                                          lower_char))
-        with self.assertWarns(DeprecationWarning):
+        self.assertRegex(str(warns.warnings[0].message),
+                         'Flags not at the start')
+        self.assertEqual(warns.warnings[0].filename, __file__)
+        with self.assertWarns(DeprecationWarning) as warns:
             self.assertTrue(re.fullmatch('($)?(?(1)|(?i)' + upper_char + ')',
                                          lower_char))
+        self.assertRegex(str(warns.warnings[0].message),
+                         'Flags not at the start')
+        self.assertEqual(warns.warnings[0].filename, __file__)
 
 
     def test_dollar_matches_twice(self):
diff --git a/Misc/NEWS b/Misc/NEWS
index bfb14c1..567f409 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -36,6 +36,10 @@ Core and Builtins
 Library
 -------
 
+- bpo-30375: Warnings emitted when compile a regular expression now always
+  point to the line in the user code.  Previously they could point into inners
+  of the re module if emitted from inside of groups or conditionals.
+
 - bpo-30048: Fixed ``Task.cancel()`` can be ignored when the task is
   running coroutine and the coroutine returned without any more ``await``.