reintroduce parsing of string interpolations nested deeper than 2 times

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## \[Unreleased\]
 
+### Added
+
+- Possibility to parse deeply nested interpolations (formerly a Limitation), Thanks again, @weaversam8 ([#223](https://github.com/amplify-education/python-hcl2/pull/223))
+
 ### Fixed
 
 - Issue parsing ellipsis in a separate line within `for` expression ([#221](https://github.com/amplify-education/python-hcl2/pull/221))

README.md

@@ -87,33 +87,15 @@ We’ll try to answer any PR’s promptly.
 
 ## Limitations
 
-### Error parsing string interpolations nested more than 2 times
-
-- Parsing following example is expected to throw out an exception and fail:
-  ```terraform
-  locals {
-    foo = "foo"
-    name = "prefix1-${"prefix2-${"${local.foo}-bar"}"}" //should interpolate into "prefix1-prefix2-foo-bar" but fails
-  }
-  ```
-  We recommend working around this by modifying the configuration in the following manner:
-  ```terraform
-  locals {
-    foo = "foo"
-    foo_bar = "${local.foo}-bar"
-    name = "prefix1-${"prefix2-${local.foo_bar}"}" //interpolates into "prefix1-prefix2-foo-bar"
-  }
-  ```
-
 ### Using inline expression as an object key
 
 - Object key can be an expression as long as it is wrapped in parentheses:
   ```terraform
-    locals {
-      foo = "bar"
-      baz = {
-        (format("key_prefix_%s", local.foo)) : "value"
-        # format("key_prefix_%s", local.foo) : "value" this will fail
-      }
+  locals {
+    foo = "bar"
+    baz = {
+      (format("key_prefix_%s", local.foo)) : "value"
+      # format("key_prefix_%s", local.foo) : "value" this will fail
     }
+  }
   ```

hcl2/hcl2.lark

@@ -1,7 +1,7 @@
 start : body
 body : (new_line_or_comment? (attribute | block))* new_line_or_comment?
 attribute : identifier EQ expression
-block : identifier (identifier | STRING_LIT)* new_line_or_comment? "{" body "}"
+block : identifier (identifier | STRING_LIT | string_with_interpolation)* new_line_or_comment? "{" body "}"
 new_line_or_comment: ( NL_OR_COMMENT )+
 NL_OR_COMMENT: /\n[ \t]*/ | /#.*\n/ | /\/\/.*\n/ | /\/\*(.|\n)*?(\*\/)/
 
@@ -45,6 +45,7 @@ expr_term : LPAR new_line_or_comment? expression new_line_or_comment? RPAR
             | float_lit
             | int_lit
             | STRING_LIT
+            | string_with_interpolation
             | tuple
             | object
             | function_call
@@ -59,10 +60,10 @@ expr_term : LPAR new_line_or_comment? expression new_line_or_comment? RPAR
             | for_tuple_expr
             | for_object_expr
 
-STRING_LIT : "\"" (STRING_CHARS | INTERPOLATION)* "\""
-STRING_CHARS : /(?:(?!\${)([^"\\]|\\.))+/+ // any character except '"" unless inside a interpolation string
-NESTED_INTERPOLATION : "${" /[^}]+/ "}"
-INTERPOLATION : "${" (/(?:(?!\${)([^}]))+/ | NESTED_INTERPOLATION)+ "}"
+STRING_LIT : "\"" STRING_CHARS? "\""
+STRING_CHARS : /(?:(?!\${)([^"\\]|\\.|\$\$))+/ // any character except '"', including escaped $$
+string_with_interpolation: "\"" (STRING_CHARS)* interpolation_maybe_nested (STRING_CHARS | interpolation_maybe_nested)* "\""
+interpolation_maybe_nested: "${" expression "}"
 
 
 int_lit : NEGATIVE_DECIMAL? DECIMAL+ | NEGATIVE_DECIMAL+

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

@@ -1 +1 @@
-{"locals": [{"simple_interpolation": "prefix:${var.foo}-suffix", "embedded_interpolation": "(long substring without interpolation); ${module.special_constants.aws_accounts[\"aaa-${local.foo}-${local.bar}\"]}/us-west-2/key_foo", "escaped_interpolation": "prefix:$${aws:username}-suffix"}]}
+{"locals": [{"simple_interpolation": "prefix:${var.foo}-suffix", "embedded_interpolation": "(long substring without interpolation); ${module.special_constants.aws_accounts[\"aaa-${local.foo}-${local.bar}\"]}/us-west-2/key_foo", "deeply_nested_interpolation": "prefix1-${\"prefix2-${\"prefix3-${local.foo}\"}\"}", "escaped_interpolation": "prefix:$${aws:username}-suffix"}]}

test/helpers/terraform-config/string_interpolations.tf

@@ -1,5 +1,6 @@
 locals {
   simple_interpolation = "prefix:${var.foo}-suffix"
   embedded_interpolation = "(long substring without interpolation); ${module.special_constants.aws_accounts["aaa-${local.foo}-${local.bar}"]}/us-west-2/key_foo"
+  deeply_nested_interpolation = "prefix1-${"prefix2-${"prefix3-${local.foo}"}"}"
   escaped_interpolation = "prefix:$${aws:username}-suffix"
 }

test/unit/test_builder.py

@@ -73,6 +73,7 @@ def test_locals_embedded_interpolation_tf(self):
             "simple_interpolation": "prefix:${var.foo}-suffix",
             "embedded_interpolation": "(long substring without interpolation); "
             '${module.special_constants.aws_accounts["aaa-${local.foo}-${local.bar}"]}/us-west-2/key_foo',
+            "deeply_nested_interpolation": 'prefix1-${"prefix2-${"prefix3-${local.foo}"}"}',
             "escaped_interpolation": "prefix:$${aws:username}-suffix",
         }