do not add trailing comma to object elements during dict -> hcl2 reconstruction

hcl2/hcl2.lark

@@ -37,6 +37,7 @@ DOUBLE_PIPE : "||"
 PLUS : "+"
 LPAR : "("
 RPAR : ")"
+COMMA : ","
 
 expr_term : LPAR new_line_or_comment? expression new_line_or_comment? RPAR
             | float_lit
@@ -71,7 +72,7 @@ EXP_MARK : ("e" | "E") ("+" | "-")? DECIMAL+
 EQ : /[ \t]*=(?!=|>)/
 
 tuple : "[" (new_line_or_comment* expression new_line_or_comment* ",")* (new_line_or_comment* expression)? new_line_or_comment* "]"
-object : "{" new_line_or_comment? (new_line_or_comment* (object_elem | (object_elem ",")) new_line_or_comment*)* "}"
+object : "{" new_line_or_comment? (new_line_or_comment* (object_elem | (object_elem COMMA)) new_line_or_comment*)* "}"
 object_elem : object_elem_key ( EQ | ":") expression
 object_elem_key : float_lit | int_lit | identifier | STRING_LIT
 

hcl2/transformer.py

@@ -5,6 +5,7 @@
 from collections import namedtuple
 from typing import List, Dict, Any
 
+from lark import Token
 from lark.tree import Meta
 from lark.visitors import Transformer, Discard, _DiscardType, v_args
 
@@ -111,6 +112,11 @@ def object(self, args: List) -> Dict:
         args = self.strip_new_line_tokens(args)
         result: Dict[str, Any] = {}
         for arg in args:
+            if (
+                isinstance(arg, Token) and arg.type == "COMMA"
+            ):  # skip optional comma at the end of object element
+                continue
+
             result.update(arg)
         return result
 

test/helpers/terraform-config/locals_embedded_condition.tf

@@ -1,7 +1,7 @@
 locals {
   terraform = {
-    channels = (local.running_in_ci ? local.ci_channels : local.local_channels),
-    authentication = [],
-    foo = null,
+    channels = (local.running_in_ci ? local.ci_channels : local.local_channels)
+    authentication = []
+    foo = null
   }
 }