bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. (#1490)

Now allowed several subsequential inline modifiers at the start of the
pattern (e.g. '(?i)(?s)...').  In verbose mode whitespaces and comments
now are allowed before and between inline modifiers (e.g.
'(?x) (?i) (?s)...').

1 files changed, 5 insertions, 7 deletions

diff --git a/Lib/sre_parse.py b/Lib/sre_parse.py
index ab37fd3fe2..d8d1bd552f 100644
--- a/Lib/sre_parse.py
+++ b/Lib/sre_parse.py
@@ -412,7 +412,7 @@ def _parse_sub(source, state, verbose, nested=True):
     sourcematch = source.match
     start = source.tell()
     while True:
-        itemsappend(_parse(source, state, verbose))
+        itemsappend(_parse(source, state, verbose, not nested and not items))
         if not sourcematch("|"):
             break
 
@@ -466,7 +466,7 @@ def _parse_sub_cond(source, state, condgroup, verbose):
     subpattern.append((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
     return subpattern
 
-def _parse(source, state, verbose):
+def _parse(source, state, verbose, first=False):
     # parse a simple pattern
     subpattern = SubPattern(state)
 
@@ -730,10 +730,9 @@ def _parse(source, state, verbose):
                     state.checklookbehindgroup(condgroup, source)
                 elif char in FLAGS or char == "-":
                     # flags
-                    pos = source.pos
                     flags = _parse_flags(source, state, char)
                     if flags is None:  # global flags
-                        if pos != 3:  # "(?x"
+                        if not first or subpattern:
                             import warnings
                             warnings.warn(
                                 'Flags not at the start of the expression %s%s' % (
@@ -742,6 +741,8 @@ def _parse(source, state, verbose):
                                 ),
                                 DeprecationWarning, stacklevel=7
                             )
+                        if (state.flags & SRE_FLAG_VERBOSE) and not verbose:
+                            raise Verbose
                         continue
                     add_flags, del_flags = flags
                     group = None
@@ -795,9 +796,6 @@ def _parse_flags(source, state, char):
                 msg = "unknown flag" if char.isalpha() else "missing -, : or )"
                 raise source.error(msg, len(char))
     if char == ")":
-        if ((add_flags & SRE_FLAG_VERBOSE) and
-            not (state.flags & SRE_FLAG_VERBOSE)):
-            raise Verbose
         state.flags |= add_flags
         return None
     if add_flags & GLOBAL_FLAGS: