native: keep same behavior on Python 3.10

CHANGES.rst

@@ -7,6 +7,8 @@ Unreleased
 
 -   Fix traceback rewriting internals for Python 3.10 and 3.11.
     :issue:`1535`
+-   Fix how the native environment treats leading and trailing spaces
+    when parsing values on Python 3.10. :pr:`1537`
 
 
 Version 3.0.2

src/jinja2/nativetypes.py

@@ -1,5 +1,6 @@
 import typing as t
 from ast import literal_eval
+from ast import parse
 from itertools import chain
 from itertools import islice
 
@@ -33,7 +34,12 @@ def native_concat(values: t.Iterable[t.Any]) -> t.Optional[t.Any]:
         raw = "".join([str(v) for v in chain(head, values)])
 
     try:
-        return literal_eval(raw)
+        return literal_eval(
+            # In Python 3.10+ ast.literal_eval removes leading spaces/tabs
+            # from the given string. For backwards compatibility we need to
+            # parse the string ourselves without removing leading spaces/tabs.
+            parse(raw, mode="eval")
+        )
     except (ValueError, SyntaxError, MemoryError):
         return raw
 

tests/test_nativetypes.py

@@ -147,3 +147,9 @@ def test_no_intermediate_eval(env):
 def test_spontaneous_env():
     t = NativeTemplate("{{ true }}")
     assert isinstance(t.environment, NativeEnvironment)
+
+
+def test_leading_spaces(env):
+    t = env.from_string(" {{ True }}")
+    result = t.render()
+    assert result == " True"