Linter: implement the rule to update definitions to $defs

[Karan-Palan]

No description provided.

[Karan-Palan]

@jviotti , for this rule I have used the rereference method. Ptal if you have any comments

[jviotti]

Suggested change

	"`definitions` is superseded by `$defs` starting in draft-2019-09. "
	"`definitions` was superseded by `$defs` in 2019-09 and later versions. "

[jviotti]

Not for this rule, but another rule that just occurred to me is that you can detect schemas in definitions or $defs that the rest of the schema is never referencing. It would be an unused schema definition. That also means we can check for empty definitions or $defs and remove those

[jviotti]

Can you try a more complicated pointer? Like a schema that has a nested schema that defines $defs and then it is referenced from the top as #/foo/bar/$defs/baz or something?

[jviotti]

Also with a nested schema resource maybe. Like

{
    ...
    "$ref": "nested#/definitions/foo",
    ...
    "$defs": {
      "nested": {
        "$id": "nested",
        ...
        "definitions": {
          "foo": {
            "type": "string"
          }
        }
      }
    }  
}

[jviotti]

I think your implementation is too complicated. I looked around, and I remembered I did something like this (definitions to $defs) internally in the test suite of the transformer. You can steal the logic from there:

core/test/jsonschema/jsonschema_transform_rules.h

Lines 284 to 315 in 4efa2d5

	class ExampleRuleDefinitionsToDefsWithRereference final
	: public sourcemeta::core::SchemaTransformRule {
	public:
	ExampleRuleDefinitionsToDefsWithRereference()
	: sourcemeta::core::SchemaTransformRule(
	"example_rule_definitions_to_defs_with_rereference",
	"Rename `definitions` to `$defs`") {};
	[[nodiscard]] auto condition(const sourcemeta::core::JSON &schema,
	const sourcemeta::core::JSON &,
	const sourcemeta::core::Vocabularies &,
	const sourcemeta::core::SchemaFrame &,
	const sourcemeta::core::SchemaFrame::Location &,
	const sourcemeta::core::SchemaWalker &,
	const sourcemeta::core::SchemaResolver &) const
	-> sourcemeta::core::SchemaTransformRule::Result override {
	return schema.defines("definitions") && !schema.defines("$defs");
	}
	auto transform(sourcemeta::core::JSON &schema) const -> void override {
	schema.rename("definitions", "$defs");
	}
	[[nodiscard]] auto rereference(const std::string &,
	const sourcemeta::core::Pointer &,
	const sourcemeta::core::Pointer &target,
	const sourcemeta::core::Pointer &current) const
	-> sourcemeta::core::Pointer override {
	return target.rebase(current.concat({"definitions"}),
	current.concat({"$defs"}));
	}
	};