Validation and CI

Generate validation methods

Add --validate to the generation directive and a matching stub to the build-tagged registration file:

//go:generate go tool polytype --validate

//go:build jsonschema

func (ToolInput) Schema() json.RawMessage     { panic("not implemented") }
func (ToolInput) ValidateJSON(_ []byte) error { panic("not implemented") }

var _ = polytype.Declare(ToolInput.Schema)

go generate ./...
go mod tidy

The generated ValidateJSON([]byte) error compiles the schema once at startup. Validation covers required fields, types, unknown properties, enum membership, and nested structure. Schema-validation failures can be inspected as *jsonschemav6.ValidationError; malformed JSON may instead return a parsing error.

If a later generation command omits --validate, polytype refuses to remove an existing generated ValidateJSON method. Restore the flag, or pass --force when removing validation is intentional.

import (
    "errors"
    "log"

    jsonschemav6 "github.com/santhosh-tekuri/jsonschema/v6"
)

func validateToolInput(data []byte) error {
    if err := (ToolInput{}).ValidateJSON(data); err != nil {
        var validationErr *jsonschemav6.ValidationError
        if errors.As(err, &validationErr) {
            log.Printf("invalid field: %s", validationErr.InstanceLocation)
        }
        return err
    }
    return nil
}

Fail CI on drift

JSONSCHEMA_NO_CHANGES flows through every go generate directive and makes the generator fail without writing schema files or requested TypeScript output when either would change. Generation can still update jsonschema_gen.go when those artifacts are unchanged, so pair the command with a Git status check:

- name: Check generated schemas and TypeScript declarations
  run: JSONSCHEMA_NO_CHANGES=1 go generate ./... && test -z "$(git status --porcelain)"

For repositories with generators that do not understand JSONSCHEMA_NO_CHANGES, use the broader fallback:

- name: Check all generated files
  run: go generate ./... && test -z "$(git status --porcelain)"

Run go test ./... after the drift check so tests execute against the same generated state that will be committed.

YAML input

polytype generates no YAML methods, and generated consumer code imports no YAML library. Convert YAML to a generic value with the library your application already uses, marshal that value to JSON, then call ValidateJSON and decode with encoding/json. Property names come from json tags. The repository’s test dependency graph may carry a YAML library transitively.