Make fidlgen_dart optional

This makes the fidlgen_dart binary optional, and shows an error in the
client if it isn't available. This will unblock deploying fidlbolt
regularly again, since fidlgen_dart isn't in fuchsia.git anymore.

I made the Makefile accept a FIDLBOLT_PATH environment variable to
specify additional search paths for `make run DEPLOYMENT=0`, which I can
use to specify a local path to fidlgen_dart.

I also updated the experimental flags passed to fidlc to match the
current defaults in fuchsia.git.

Change-Id: I1aebf953d3526188fc1cde099d4a1e86d4156e45
Reviewed-by: Ian McKellar <>
3 files changed
tree: 3158c19fba12b59fa69a7eea8735a29296184921
  1. backend/
  2. frontend/
  3. .dockerignore
  4. .gitignore
  8. Dockerfile
  10. Makefile


fidlbolt is web app for exploring FIDL code and bytes, inspired by Matt Godbolt's Compiler Explorer.

Get started

To run a local fidlbolt server:

  1. Follow the Fuchsia: Get Started guide.
  2. Build FIDL tools: fx build host_x64/{fidlc,fidlgen_{cpp,hlcpp,rust,go,dart}} zircon/tools.
  3. Ensure that you have Go and Node.js installed.
  4. Build and run with make run.
  5. View the app at http://localhost:8080.

If you don't want changes in the Fuchsia tree (e.g. rebuilding fidlc or changing FIDL libraries) to affect the running fidlbolt, run ./ and use make run DEPLOYMENT=1 instead.



The backend is written in Go. It uses net/http to serve static files and handle POST requests.


The frontend is written in Elm and TypeScript. It uses webpack for bundling.

To set up the frontend:

  1. Install Node.js and npm. On Debian-based systems, use sudo apt-get install npm.
  2. cd frontend && npm ci (using ci instead of install ensures a repeatable build).

Then, use one of the commands listed in npm run:

  • npm run dev: build in development mode
  • npm run watch: rebuild in development mode on every file change
  • npm run tc: typecheck TypeScript files
  • npm run lint: run eslint on TypeScript files
  • npm run fix: format and fix lint issues in TypeScript and Elm files
  • npm run build: build in production mode

The build commands read files in frontend/src/ and generate output in frontend/dist/.


If you are developing on Linux, ./ provides an easy workflow. It automatically watches code in the frontend (using npm run watch) and backend (using inotifywait), rebuilding and restarting the server as necessary. It does not perform hot/live reloading: you still need to refresh the browser manually to see changes.


Before making a CL, always run make format.


The project uses Docker for containerized deployment.

To build and run a new image locally:

  1. Install Docker. On Debian-based systems, use sudo apt-get install docker-ce.
  2. ./
  3. docker image build -t fidlbolt .
  4. docker container run --publish 8080:8080 --detach --name fb fidlbolt

You might need to use sudo with the Docker commands.