mochi_codegen

Code generation (TypeScript types, GraphQL SDL, Gleam types + resolver stubs) and CLI for mochi GraphQL.

Installation

gleam add mochi_codegen

CLI

gleam run -m mochi_codegen/cli -- init       # create mochi.config.yaml
gleam run -m mochi_codegen/cli -- generate   # generate from config

Config (mochi.config.yaml)

schema: "graphql/*.graphql"

# Optional: generate resolver boilerplate from .gql client operation files
operations_input: "src/graphql/**/*.gql"

output:
  typescript: "src/generated/types.ts"   # TypeScript type definitions
  gleam_types: "src/api/domain/"         # Gleam domain types (dir = one file per schema)
  resolvers: "src/api/schema/"           # Gleam resolver stubs (preserved on regen)
  operations: "src/api/schema/"          # Gleam operation resolvers (from .gql files)
  sdl: null                              # Normalised SDL (omit to skip)

gleam:
  types_module_prefix: "api/domain"
  resolvers_module_prefix: "api/schema"
  type_suffix: "_types"
  resolver_suffix: "_resolvers"
  generate_docs: true

Output paths ending in / produce one file per schema file. Paths without / merge all schemas into a single file.

Write policies

Output	Policy
typescript, sdl	Always overwrite
gleam_types	Overwrite only when content changed
resolvers, operations	Never overwrite existing functions — only appends new stubs

Validation and error surfaces

• Unknown operation fields fail the build. If an operations_input .gql file references a root field that doesn't exist in the schema, generate exits with UnknownOperationFields listing the offending fields. The emitted Gleam (if you force generation some other way) contains a <MISSING:field_name> sentinel rather than a generic TODO, so it's greppable.
• Argument defaults round-trip in SDL. Scalar defaults (Bool, Int, Float, String) are rendered in sdl output. Complex defaults (lists, objects, enums) are omitted rather than emitted as broken syntax — mochi/schema stores them as type-erased Option(Dynamic) which isn't reversible for non-scalars.
• TypeScript enum values are identifier-checked. Values that don't match [_A-Za-z][_0-9A-Za-z]* (which GraphQL itself forbids, but custom schema builders can bypass) are replaced with a // Skipped: ... comment rather than a broken enum member. Grep the output for // Skipped: to find them.
• Playground endpoints are escaped. graphiql, playground, apollo_sandbox, and simple_explorer all escape the endpoint URL before interpolating it into inline JS / HTML. Callers can pass any string without worrying about breaking the generated page.
• Unmapped type-builder fields surface in the CLI output. Resolver generation emits // TODO: register field "<name>" for types the generator can't map (uncommon custom scalars, unsupported non-null list shapes). The CLI success line is decorated with the count — e.g. Generated resolvers (3 unmapped fields — see TODO comments): src/generated/schema_resolvers.gleam — so these don't silently accumulate across regenerations.

Programmatic Usage

import mochi_codegen

let ts   = mochi_codegen.to_typescript(schema)
let sdl  = mochi_codegen.to_sdl(schema)
let html = mochi_codegen.graphiql("/graphql")

License

Apache-2.0