hcl2.builder.Builder - nested blocks support (#214)

Author: kkozik-amplify

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## \[Unreleased\]
 
+### Added
+
+- `hcl2.builder.Builder` - nested blocks support ([#214](https://github.com/amplify-education/python-hcl2/pull/214))
+
 ### Fixed
 
 - Issue parsing parenthesesed identifier (reference) as an object key ([#212](https://github.com/amplify-education/python-hcl2/pull/212))

hcl2/builder.py

@@ -1,7 +1,10 @@
 """A utility class for constructing HCL documents from Python code."""
-
 from typing import List, Optional
 
+from collections import defaultdict
+
+from hcl2.const import START_LINE_KEY, END_LINE_KEY
+
 
 class Builder:
     """
@@ -15,49 +18,69 @@ class Builder:
     """
 
     def __init__(self, attributes: Optional[dict] = None):
-        self.blocks: dict = {}
+        self.blocks: dict = defaultdict(list)
         self.attributes = attributes or {}
 
     def block(
-        self, block_type: str, labels: Optional[List[str]] = None, **attributes
+        self,
+        block_type: str,
+        labels: Optional[List[str]] = None,
+        __nested_builder__: Optional["Builder"] = None,
+        **attributes
     ) -> "Builder":
         """Create a block within this HCL document."""
+
+        if __nested_builder__ is self:
+            raise ValueError(
+                "__nested__builder__ cannot be the same instance as instance this method is called on"
+            )
+
         labels = labels or []
         block = Builder(attributes)
 
-        # initialize a holder for blocks of that type
-        if block_type not in self.blocks:
-            self.blocks[block_type] = []
-
         # store the block in the document
-        self.blocks[block_type].append((labels.copy(), block))
+        self.blocks[block_type].append((labels.copy(), block, __nested_builder__))
 
         return block
 
     def build(self):
         """Return the Python dictionary for this HCL document."""
-        body = {
-            "__start_line__": -1,
-            "__end_line__": -1,
-            **self.attributes,
-        }
+        body = defaultdict(list)
 
-        for block_type, blocks in self.blocks.items():
+        body.update(
+            {
+                START_LINE_KEY: -1,
+                END_LINE_KEY: -1,
+                **self.attributes,
+            }
+        )
 
-            # initialize a holder for blocks of that type
-            if block_type not in body:
-                body[block_type] = []
+        for block_type, blocks in self.blocks.items():
 
-            for labels, block_builder in blocks:
+            for labels, block_builder, nested_blocks in blocks:
                 # build the sub-block
                 block = block_builder.build()
 
+                if nested_blocks:
+                    self._add_nested_blocks(block, nested_blocks)
+
                 # apply any labels
-                labels.reverse()
-                for label in labels:
+                for label in reversed(labels):
                     block = {label: block}
 
                 # store it in the body
                 body[block_type].append(block)
 
         return body
+
+    def _add_nested_blocks(
+        self, block: dict, nested_blocks_builder: "Builder"
+    ) -> "dict":
+        """Add nested blocks defined within another `Builder` instance to the `block` dictionary"""
+        nested_block = nested_blocks_builder.build()
+        for key, value in nested_block.items():
+            if key not in (START_LINE_KEY, END_LINE_KEY):
+                if key not in block.keys():
+                    block[key] = []
+                block[key].extend(value)
+        return block

hcl2/const.py

@@ -0,0 +1,4 @@
+"""Module for various constants used across the library"""
+
+START_LINE_KEY = "__start_line__"
+END_LINE_KEY = "__end_line__"

hcl2/reconstructor.py

@@ -10,6 +10,8 @@
 from lark.reconstruct import Reconstructor
 from lark.tree_matcher import is_discarded_terminal
 from lark.visitors import Transformer_InPlace
+
+from hcl2.const import START_LINE_KEY, END_LINE_KEY
 from hcl2.parser import reconstruction_parser
 
 
@@ -423,7 +425,7 @@ def _dict_is_a_block(self, sub_obj: Any) -> bool:
 
         # 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():
+        if START_LINE_KEY in sub_obj.keys() or END_LINE_KEY in sub_obj.keys():
             return True
 
         # if the objects in the array have no metadata and more than 2 keys and
@@ -454,15 +456,16 @@ def _calculate_block_labels(self, block: dict) -> Tuple[List[str], dict]:
 
         # __start_line__ and __end_line__ metadata are not labels
         if (
-            "__start_line__" in potential_body.keys()
-            or "__end_line__" in potential_body.keys()
+            START_LINE_KEY in potential_body.keys()
+            or END_LINE_KEY in potential_body.keys()
         ):
             return [curr_label], potential_body
 
         # recurse and append the label
         next_label, block_body = self._calculate_block_labels(potential_body)
         return [curr_label] + next_label, block_body
 
+    # pylint:disable=R0914
     def _transform_dict_to_body(self, hcl_dict: dict, level: int) -> Tree:
         # we add a newline at the top of a body within a block, not the root body
         # >2 here is to ignore the __start_line__ and __end_line__ metadata
@@ -473,7 +476,7 @@ def _transform_dict_to_body(self, hcl_dict: dict, level: int) -> Tree:
 
         # iterate through each attribute or sub-block of this block
         for key, value in hcl_dict.items():
-            if key in ["__start_line__", "__end_line__"]:
+            if key in [START_LINE_KEY, END_LINE_KEY]:
                 continue
 
             # construct the identifier, whether that be a block type name or an attribute key
@@ -499,7 +502,12 @@ def _transform_dict_to_body(self, hcl_dict: dict, level: int) -> Tree:
                         [identifier_name] + block_label_tokens + [block_body],
                     )
                     children.append(block)
-                    children.append(self._newline(level, count=2))
+                    # add empty line after block
+                    new_line = self._newline(level - 1)
+                    # add empty line with indentation for next element in the block
+                    new_line.children.append(self._newline(level).children[0])
+
+                    children.append(new_line)
 
             # if the value isn't a block, it's an attribute
             else:
@@ -562,7 +570,7 @@ def _transform_value_to_expr_term(self, value, level) -> Union[Token, Tree]:
 
             # iterate through the items and add them to the object
             for i, (k, dict_v) in enumerate(value.items()):
-                if k in ["__start_line__", "__end_line__"]:
+                if k in [START_LINE_KEY, END_LINE_KEY]:
                     continue
 
                 value_expr_term = self._transform_value_to_expr_term(dict_v, level + 1)

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

@@ -1,12 +1,34 @@
 {
-    "block": [
-        {
-            "a": 1
-        },
-        {
-            "label": {
-                "b": 2
-            }
-        }
+ "block": [
+  {
+   "a": 1
+  },
+  {
+   "label": {
+    "b": 2,
+    "nested_block_1": [
+     {
+      "a": {
+       "foo": "bar"
+      }
+     },
+     {
+      "a": {
+       "b": {
+        "bar": "foo"
+       }
+      }
+     },
+     {
+      "foobar": "barfoo"
+     }
+    ],
+    "nested_block_2": [
+     {
+      "barfoo": "foobar"
+     }
     ]
+   }
+  }
+ ]
 }

test/helpers/terraform-config/blocks.tf

@@ -4,4 +4,19 @@ block {
 
 block "label" {
   b = 2
+  nested_block_1 "a" {
+    foo = "bar"
+  }
+
+  nested_block_1 "a" "b" {
+    bar = "foo"
+  }
+
+  nested_block_1 {
+    foobar = "barfoo"
+  }
+
+  nested_block_2 {
+    barfoo = "foobar"
+  }
 }

test/unit/test_builder.py

@@ -22,10 +22,15 @@ class TestBuilder(TestCase):
     maxDiff = None
 
     def test_build_blocks_tf(self):
-        builder = hcl2.Builder()
+        nested_builder = hcl2.Builder()
+        nested_builder.block("nested_block_1", ["a"], foo="bar")
+        nested_builder.block("nested_block_1", ["a", "b"], bar="foo")
+        nested_builder.block("nested_block_1", foobar="barfoo")
+        nested_builder.block("nested_block_2", barfoo="foobar")
 
+        builder = hcl2.Builder()
         builder.block("block", a=1)
-        builder.block("block", ["label"], b=2)
+        builder.block("block", ["label"], __nested_builder__=nested_builder, b=2)
 
         self.compare_filenames(builder, "blocks.tf")