gh-109747: Improve errors for unsupported look-behind patterns (GH-109859)

Now re.error is raised instead of OverflowError or RuntimeError for
too large width of look-behind pattern.

The limit is increased to 2**32-1 (was 2**31-1).

Lib/re/_parser.py

@@ -67,6 +67,10 @@ FLAGS = {
 TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
 GLOBAL_FLAGS = SRE_FLAG_DEBUG
 
+# Maximal value returned by SubPattern.getwidth().
+# Must be larger than MAXREPEAT, MAXCODE and sys.maxsize.
+MAXWIDTH = 1 << 64
+
 class State:
     # keeps track of state for parsing
     def __init__(self):
@@ -177,7 +181,7 @@ class SubPattern:
         lo = hi = 0
         for op, av in self.data:
             if op is BRANCH:
-                i = MAXREPEAT - 1
+                i = MAXWIDTH
                 j = 0
                 for av in av[1]:
                     l, h = av.getwidth()
@@ -196,7 +200,10 @@ class SubPattern:
             elif op in _REPEATCODES:
                 i, j = av[2].getwidth()
                 lo = lo + i * av[0]
-                hi = hi + j * av[1]
+                if av[1] == MAXREPEAT and j:
+                    hi = MAXWIDTH
+                else:
+                    hi = hi + j * av[1]
             elif op in _UNITCODES:
                 lo = lo + 1
                 hi = hi + 1
@@ -216,7 +223,7 @@ class SubPattern:
                 hi = hi + j
             elif op is SUCCESS:
                 break
-        self.width = min(lo, MAXREPEAT - 1), min(hi, MAXREPEAT)
+        self.width = min(lo, MAXWIDTH), min(hi, MAXWIDTH)
         return self.width
 
 class Tokenizer: