WIP: Postgraphile v5 Support (#58)

[FelixZY]

Description

This PR aims to migrate the plugin to Postgraphile v5.

#58

Performance impact

unknown

Security impact

unknown

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[FelixZY]

I'm still quite new to Postgraphile and have limited experience of either v4 or v5 plugins. Please let me know if I'm doing something strange or unexpected!

---

I'm finding a few things hard to understand and am unsure about my direction. @benjie, would you mind helping me out with some feedback?

The biggest issue right now is PostgisRegisterTypesPlugin.ts. My understanding is that i need to do something like the following:

declare global {
  namespace GraphileBuild {
    interface ScopeObject {
      isPgGISType?: boolean;
    }
  }
}

export default makeExtendSchemaPlugin((build) => {
  const asGeoJson =
    // HELP: "Property 'pgRegistry' does not exist on type 'BuildInput'" - not sure what the problem is
    build.input.pgRegistry.pgResources[
      // HELP: Do I need to use build.inflection here?
      // The old code uses
      // `sql.identifier(POSTGIS.namespaceName || "public", "st_asgeojson")`
      build.inflection.builtin("st_asgeojson")
    ];

  return {
    typeDefs: gql`
      # I've extracted these from the GeoJSON RFC.
      # Their final shape is still a WIP (I also want to reduce the risk of breakage)
      interface GeoJsonObject {
        geojson: String!
        type: String
        bbox: [Float!]
        srid: Int!
      }
      interface GeometryObject implements GeoJsonObject {
        type: String!
      }
      scalar Position
      type PointObject implements GeometryObject {
        coordinates: Position
      }
      ...
    `,
    plans: {
      GeoJsonObject: {
        geojson: {
          plan() {
            return asGeoJson
              .execute(
                /*
                * HELP: No idea what to put in here!
                * I would assume some sort of reference to
                * e.g. `$parentPlan: ExecutableStep` but I'm
                * not sure how to access that in this scope
                * (I noticed it could be accessed from
                * `build.registerObjectType` when looking at
                * https://github.com/graphile/crystal/blob/main/graphile-build/graphile-build-pg/src/plugins/PgTypesPlugin.ts#L378
                * ).
                */
              );
          },
        },
      },
      GeometryObject: {
        /* ... */
      },
      Position: GraphQlPositionScalar,
      PointObject: {
        /* ... */
      },
      // ...
    },
  };
}, "PostgisRegisterTypesPlugin");

(I have marked areas where I could use some specific help with HELP:)

Is this in the right ballpark? Could you point me to some other plugins that make use of SQL function calls to aid me as reference material?