[Python] no stray parentheses in regexp patterns (#4133)

* [Python] no stray parentheses in regexp patterns

This commit scopes stray brackets normally as those may appear in partial
patterns. Correct parentheses matching is not always possible and causes
valid closing brackets to be scoped illegal.

* [Python] Prepend patterns

Python/Embeddings/RegExp (for Python).sublime-syntax

@@ -56,3 +56,11 @@ contexts:
         1: punctuation.definition.capture-group-name.begin.regexp
         2: variable.other.backref-and-recursion.regexp
         3: punctuation.definition.capture-group-name.end.regexp
+
+  literals:
+    - meta_prepend: true
+    # no illegal parentheses in concatenated patterns
+    - match: \]
+      scope: punctuation.definition.set.end.regexp
+    - match: \)
+      scope: punctuation.section.group.end.regexp

Python/tests/syntax_test_python_strings.py

@@ -1300,6 +1300,11 @@
 #                                                        ^^^^ meta.modifier
 #                                                          ^ storage.modifier.mode
 
+match = re.match(r"([^" + charset + r"]*)", line)
+#                  ^ punctuation.section.group.begin.regexp
+#                   ^ punctuation.definition.set.begin.regexp
+#                                     ^ punctuation.definition.set.end.regexp
+#                                       ^ punctuation.section.group.end.regexp
 
 ###############################
 # f-strings