References to data sources aren't fully tracked

[ajkerrigan]

We don't currently track references from resource blocks to data blocks, because upstream we don't really know what we're going to get back. For static analysis those references can still be useful though, for instance...

data "aws_rds_reserved_instance_offering" "example" {
  db_instance_class   = "db.m7g.large"
}

resource "aws_rds_reserved_instance" "example" {
  offering_id    = data.aws_rds_reserved_instance_offering.example.offering_id
  instance_count = 1
}

resource "aws_db_instance" "example" {
  instance_class          = aws_rds_reserved_instance.example.db_instance_class
}

Produces the dump below. We can see traces of references in two different spots:

Attribute Level

aws_db_instance includes this reference to aws_rds_reserved_instance for its instance_class attribute:

        "instance_class": {
          "__attribute__": "aws_rds_reserved_instance.example.db_instance_class",
          "__name__": "example"
        }

In turn, that aws_rds_reserved_instance references an offering:

        "offering_id": {
          "__attribute__": "data.aws_rds_reserved_instance_offering.example.offering_id",
          "__name__": "example",
          "__ref__": "aws_rds_reserved_instance_offering.example",
          "__type__": "aws_rds_reserved_instance_offering"
        }

Resource Level

The aws_db_instance resource's __tfmeta attribute captures its aws_rds_reserved_instance reference:

          "references": [
            {
              "id": "0c547493-9654-447a-959b-31ae3dd2cacc",
              "label": "aws_rds_reserved_instance",
              "name": "example"
            }
          ]

...but the aws_rds_reserved_instance resources does not have any references listed in its __tfmeta attribute, so the chain from aws_db_instance --> aws_rds_reserved_instance --> data.aws_rds_reserved_instance_offering is broken.

Full `tfparse.load_from_path()` output

{
    "aws_db_instance": [
        {
            "__tfmeta": {
                "filename": "rds.tf",
                "label": "aws_db_instance",
                "line_end": 12,
                "line_start": 10,
                "path": "aws_db_instance.example",
                "references": [
                    {
                        "id": "db6030c1-fad0-4d0a-a6d5-708d9e34c83a",
                        "label": "aws_rds_reserved_instance",
                        "name": "example"
                    }
                ],
                "type": "resource"
            },
            "id": "822d10d1-08f4-4886-85b4-8740bb9ea4c4",
            "instance_class": {
                "__attribute__": "aws_rds_reserved_instance.example.db_instance_class",
                "__name__": "example"
            }
        }
    ],
    "aws_rds_reserved_instance": [
        {
            "__tfmeta": {
                "filename": "rds.tf",
                "label": "aws_rds_reserved_instance",
                "line_end": 8,
                "line_start": 5,
                "path": "aws_rds_reserved_instance.example",
                "type": "resource"
            },
            "id": "db6030c1-fad0-4d0a-a6d5-708d9e34c83a",
            "instance_count": 1,
            "offering_id": {
                "__attribute__": "data.aws_rds_reserved_instance_offering.example.offering_id",
                "__name__": "example",
                "__ref__": "aws_rds_reserved_instance_offering.example",
                "__type__": "aws_rds_reserved_instance_offering"
            }
        }
    ],
    "aws_rds_reserved_instance_offering": [
        {
            "__tfmeta": {
                "filename": "rds.tf",
                "label": "aws_rds_reserved_instance_offering",
                "line_end": 3,
                "line_start": 1,
                "path": "data.aws_rds_reserved_instance_offering.example",
                "type": "data"
            },
            "db_instance_class": "db.m7g.large",
            "id": "9251a42c-9126-413c-9350-d6fc390ce42d"
        }
    ]
}