HCLReverseTransformer - rework logic recognizing blocks

Author: kkozik-amplify

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Fixed
 
 - Issue parsing dot-accessed attribute as an object key ([#209](https://github.com/amplify-education/python-hcl2/pull/209))
+- Issue discarding empty lists when transforming python dictionary into Lark Tree ([#216](https://github.com/amplify-education/python-hcl2/pull/216))
 
 ## \[7.0.0\] - 2025-03-27
 

hcl2/reconstructor.py

@@ -401,40 +401,29 @@ def _newline(self, level: int, count: int = 1) -> Tree:
             [Token("NL_OR_COMMENT", f"\n{'  ' * level}") for _ in range(count)],
         )
 
-    # rules: the value of a block is always an array of dicts,
-    # the key is the block type
-    def _list_is_a_block(self, value: list) -> bool:
-        for obj in value:
-            if not self._dict_is_a_block(obj):
-                return False
-
-        return True
-
-    def _dict_is_a_block(self, sub_obj: Any) -> bool:
-        # if the list doesn't contain dictionaries, it's not a block
-        if not isinstance(sub_obj, dict):
-            return False
+    def _is_block(self, value: Any) -> bool:
+        if isinstance(value, dict):
+            block_body = value
+            if (
+                "__start_line__" in block_body.keys()
+                or "__end_line__" in block_body.keys()
+            ):
+                return True
 
-        # if the sub object has "start_line" and "end_line" metadata,
-        # the block itself is unlabeled, but it is a block
-        if "__start_line__" in sub_obj.keys() or "__end_line__" in sub_obj.keys():
-            return True
+            try:
+                # if block is labeled, actual body might be nested
+                # pylint: disable=W0612
+                block_label, block_body = next(iter(value.items()))
+            except StopIteration:
+                # no more potential labels = nothing more to check
+                return False
 
-        # if the objects in the array have no metadata and more than 2 keys and
-        # no metadata, it's just an array of objects, not a block
-        if len(list(sub_obj)) != 1:
-            return False
+            return self._is_block(block_body)
 
-        # if the sub object has a single string key whose value is an object,
-        # it _could_ be a labeled block... but we'd have to check if the sub
-        # object is a block (recurse)
-        label = list(sub_obj)[0]
-        sub_sub_obj = sub_obj[label]
-        if self._dict_is_a_block(sub_sub_obj):
-            return True
+        if isinstance(value, list):
+            if len(value) > 0:
+                return self._is_block(value[0])
 
-        # if the objects in the array have a single key whose child is not a
-        # block, the array is just an array of objects, not a block
         return False
 
     def _calculate_block_labels(self, block: dict) -> Tuple[List[str], dict]:
@@ -474,7 +463,7 @@ def _transform_dict_to_body(self, hcl_dict: dict, level: int) -> Tree:
             identifier_name = self._name_to_identifier(key)
 
             # first, check whether the value is a "block"
-            if isinstance(value, list) and self._list_is_a_block(value):
+            if self._is_block(value):
                 for block_v in value:
                     block_labels, block_body_dict = self._calculate_block_labels(
                         block_v

test/helpers/terraform-config-json/variables.json

@@ -47,7 +47,9 @@
       "foo": "${var.account}_bar",
       "bar": {
         "baz": 1
-      }
+      },
+      "tuple": ["${local.foo}"],
+      "empty_tuple": []
     },
     {
       "route53_forwarding_rule_shares": "${{for forwarding_rule_key in keys(var.route53_resolver_forwarding_rule_shares) : \"${forwarding_rule_key}\" => {\"aws_account_ids\": \"${[for account_name in var.route53_resolver_forwarding_rule_shares[forwarding_rule_key].aws_account_names : module.remote_state_subaccounts.map[account_name].outputs[\"aws_account_id\"]]}\"}}}",

test/helpers/terraform-config/variables.tf

@@ -9,6 +9,8 @@ locals {
   bar = {
     baz : 1
   }
+  tuple = [local.foo]
+  empty_tuple = []
 }
 
 variable "azs" {