GraphQL-PPX Compatibility Validation

Objective

Validate graphql-ppx compatibility with Melange 5.0 and establish type-safe GraphQL query generation pipeline.

Background

graphql-ppx (v1.2.2, last updated 2021) needs testing with Melange 5.0. If incompatible, we'll evaluate alternatives like ppx_graphql.

Tasks

• Install graphql_ppx from OPAM
• Create test queries with graphql-ppx
• Verify ppxlib version compatibility
• Test with exported PostGraphile schema
• Configure dune for PPX preprocessing
• Validate generated types with Melange
• Document any workarounds needed
• Create fallback plan if incompatible

Test Implementation

(* test/GraphQLTest.re *)
module GetUser = [%graphql
  {|
    query GetUser($id: ID\!) {
      user(id: $id) {
        id
        email
        name
      }
    }
  |}
];

let testQuery = () => {
  let query = GetUser.make(~id="1", ());
  Js.log(query##variables);
};

Dune Configuration

(library
 (name graphql_test)
 (libraries melange.js graphql_ppx melange_apollo)
 (modes melange)
 (preprocess (pps graphql_ppx melange.ppx)))

Acceptance Criteria

• PPX processes GraphQL queries without errors
• Generated types work with Melange
• Can use types with Apollo bindings
• Schema file loading works
• Variables properly typed
• Fragments supported

Alternative Approaches

Option A: ppx_graphql

opam install ppx_graphql

Option B: Manual Types

(* If PPX fails, use manual approach *)
type userQuery = {
  id: string,
  email: string,
  name: option(string),
};

let query = {|
  query GetUser($id: ID\!) {
    user(id: $id) { id email name }
  }
|};

Option C: Generate Types from Schema

# Use graphql-codegen with custom templates
npm run codegen:types

Version Compatibility Matrix

Component	Required	Current	Status
Melange	5.0+	5.0	✅
ppxlib	<0.36.0	?	Test
graphql_ppx	1.2.2	1.2.2	Test
OCaml	4.06+	5.3	✅

Testing Strategy

1. Simple query test
2. Query with variables
3. Mutation test
4. Fragment test
5. Union types test
6. Interface types test

Priority: 🟡 High

Can work around if needed, but impacts DX significantly.

Estimated Effort: 1-2 days

Risk Mitigation

If graphql-ppx fails:

1. Try ppx_graphql (2 hours)
2. Use manual types (4 hours)
3. Build codegen solution (1 day)
4. Use PostGraphile client (2 hours)

Dependencies

• #38 PostGraphile API (need schema.graphql)
• #36 Apollo bindings (to test integration)

CI Validation

• PPX preprocessing succeeds
• Type checking passes
• Generated code compiles