capnpc_dart_builder

build_runner integration for capnpc_dart.

How the pieces fit together

  • capnpc_dart_builder (this package)
    wraps capnpc_dart's generator in a build_runner builder.
  • The generated code depends on capnproto_dart

Install

dev_dependencies:
  build_runner: ^2.4.13
  capnpc_dart_builder: ^0.1.0

dart pub get

The official capnp compiler must also be installed and on PATH. it does not parse .capnp syntax itself.

If capnp can't be launched (not installed, not on PATH, or a permissions issue), the build fails with a CapnpLaunchException:

capnp compile failed: could not launch the `capnp` command-line compiler
(No such file or directory). This usually means `capnp` is not installed or
not on PATH — install it yourself, see https://capnproto.org/install.html —
but could also be a permissions or other OS-level launch failure. Underlying
error: ProcessException: No such file or directory
  Command: capnp compile ...

Generate Dart code

build_runner only looks under lib/, so put schema files there:

# lib/schema/hello.capnp
@0xdeadbeefdeadbeef;

struct Greeting {
  name @0 :Text;
  reply @1 :Text;
}

dart run build_runner build

This writes lib/schema/hello.capnp.dart next to your schema.
Re-run after editing a schema; add --delete-conflicting-outputs if build_runner complains about stale output.

Custom import paths

Schemas that import a file outside their own package (capnp's -I-rooted imports) need an extra search root,
since build_runner can only see files inside the package being built. Add one via the builder's import_paths option in your own build.yaml:

targets:
  $default:
    builders:
      capnpc_dart_builder|capnp:
        options:
          import_paths: ["../shared_schemas"]

See the schema and code-generation guide for imports, constants, generated names, and current limitations.

Libraries

capnpc_dart_builder