Support external references

[SRetip]

Implementation for issue #201.

These changes were made based on the discussion in the issue.

I understand that this pull request can be improved, and I would appreciate any feedback and thoughts on how to make it better.

[jayvdb]

the dependencies above are alpha sorted. would be good for these new ones to also be alpha sorted

[jayvdb]

commented out code in this test

[baxterjo]

@jayvdb Bumping this

[liamwh]

@SRetip is it an idea that you resolve the merge conflicts so that the maintainers can approve and this can be merged?

[LimpidCrypto]

I'm really looking forward to this feature. I already tried using the feature branch in my project:

typify = { git = "https://github.com/agily/typify", branch = "support-external-references", package = "typify" }

I have one file schemas/common/xrp.json:

{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "$id": "https://raw.githubusercontent.com/LimpidCrypto/xrpl-models/main/schemas/common/xrp.json",
    "title": "XRP",
    "type": "object",
    "properties": {
        "currency": {
            "type": "string",
            "const": "XRP",
            "description": "The currency code for XRP."
        },
        "issuer": {
            "$ref": "https://raw.githubusercontent.com/LimpidCrypto/xrpl-models/main/schemas/types.json#/definitions/ACCOUNT",
            "description": "The empty string, because XRP is not issued by any single entity."
        }
    },
    "required": [
        "currency",
        "issuer"
    ]
}

In the properties.issuer I'm trying to reference a type in schemas/types.json:

{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "$id": "https://raw.githubusercontent.com/LimpidCrypto/xrpl-models/main/schemas/types.json",
    "definitions": {
        "ACCOUNT": {
            "type": "string",
            "description": "An XRP Ledger account address.",
            "pattern": "^r[1-9A-HJ-NP-Za-km-z]{25,34}$"
        }
    }
}

In my project I'm trying to import XRP like so:

import_types!(schema="./schemas/common/xrp.json");

But I get this uninformative error message:

error: proc macro panicked
 --> src/common/xrp.rs:4:1
  |
4 | import_types!(schema="./schemas/common/xrp.json");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: message: called `Option::unwrap()` on a `None` value

I'm new to json schemas and this library so it's very likely I just have a false understanding on how to reference to a type externally.

[LimpidCrypto]

Suggested change

	let definition_schema = if fragment[0] == "definitions" {
	let definition_schema = if ["definitions", "$defs"].contains(&fragment[0].as_str()) {

This should match both "definitions" and "$defs" as "https://json-schema.org/draft/2020-12/schema" replaced "definitions" with "$defs"

[LimpidCrypto]

My review above resolves my issue using typify-impl but still exists using typify-macro. It seems like it does not resolve the base_path in typify-impl/lib.rs::fetch_external_definitions. It's just an empty string. This is an issue when trying to determine the file_path here because of the .parent().unwrap().