refactor: Remove deprecated ast.Index usage for Python 3.9+ compatibility

Author: spookylukey

src/fluent_compiler/ast_compat.py

@@ -40,7 +40,6 @@ def NewAst(...):
 ExceptHandler = ast.ExceptHandler
 Expr = ast.Expr
 If = ast.If
-Index = ast.Index
 List = ast.List
 Load = ast.Load
 Module = ast.Module
@@ -62,6 +61,15 @@ def NewAst(...):
 keyword = ast.keyword
 walk = ast.walk
 
+# Index is deprecated in Python 3.9 and removed in 3.10+
+if sys.version_info < (3, 9):
+    Index = ast.Index
+else:
+    # In Python 3.9+, we don't need Index anymore as subscript slices
+    # directly use the value
+    def Index(value, **kwargs):
+        return value
+
 
 if sys.version_info >= (3, 8):
     Constant = ast.Constant

src/fluent_compiler/codegen.py

@@ -802,7 +802,7 @@ def __init__(self, lookup_obj, lookup_arg, expr_type=UNKNOWN_TYPE):
     def as_ast(self):
         return ast.Subscript(
             value=self.lookup_obj.as_ast(),
-            slice=ast.Index(value=self.lookup_arg.as_ast(), **DEFAULT_AST_ARGS),
+            slice=self.lookup_arg.as_ast(),
             ctx=ast.Load(),
             **DEFAULT_AST_ARGS,
         )