gh-59598: Ignore leading whitespace in JSONDecoder.raw_decode

raw_decode now ignores leading whitespace before the JSON value,
matching the behavior of decode(). Previously, passing a string like
'  {}' to raw_decode would raise JSONDecodeError.

The fix uses the existing WHITESPACE regex to skip whitespace at
any offset, preserving correct behavior with the idx parameter.

Author: mayank-dev-15

Lib/json/decoder.py

@@ -355,13 +355,13 @@ def decode(self, s, _w=WHITESPACE.match):
         containing a JSON document).
 
         """
-        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
+        obj, end = self.raw_decode(s)
         end = _w(s, end).end()
         if end != len(s):
             raise JSONDecodeError("Extra data", s, end)
         return obj
 
-    def raw_decode(self, s, idx=0):
+    def raw_decode(self, s, idx=0, _w=WHITESPACE.match):
         """Decode a JSON document from ``s`` (a ``str`` beginning with
         a JSON document) and return a 2-tuple of the Python
         representation and the index in ``s`` where the document ended.
@@ -371,7 +371,7 @@ def raw_decode(self, s, idx=0):
 
         """
         try:
-            obj, end = self.scan_once(s, idx)
+            obj, end = self.scan_once(s, idx=_w(s, idx).end())
         except StopIteration as err:
             raise JSONDecodeError("Expecting value", s, err.value) from None
         return obj, end