Fix ast parsing of indented block, closes #1

Author: kalekseev

src/extra_checks/ast.py

@@ -1,5 +1,6 @@
 import ast
 import inspect
+import textwrap
 from typing import (
     Callable,
     Dict,
@@ -34,7 +35,7 @@ def is_proxy(self) -> bool:
 
     @cached_property
     def _nodes(self) -> Iterator[ast.AST]:
-        source = inspect.getsource(self.model_cls)
+        source = textwrap.dedent(inspect.getsource(self.model_cls))
         return iter(ast.parse(source).body[0].body)  # type: ignore
 
     def _parse(self, predicate: Optional[Callable[[ast.AST], bool]] = None) -> None:

tests/example/models.py

@@ -14,9 +14,11 @@ class Meta:
         verbose_name = "Site Article"
 
 
-class Author(models.Model):
-    first_name = models.CharField(max_length=100)
-    last_name = models.CharField(max_length=100)
+if True:
+    # test that indentation doesn't break ast parser
+    class Author(models.Model):
+        first_name = models.CharField(max_length=100)
+        last_name = models.CharField(max_length=100)
 
 
 class NestedField(models.Field):