Docker sandbox

The development sandbox provides a disposable Linux environment with the current checkout of Flecha installed. It includes:

• flecha and longbow on PATH
• the bundled standard library, discovered automatically by Longbow
• Clang 18 as Flecha’s native linker
• Neovim 0.12.6 with the Flecha plugin and the host configuration when present
• a starter Longbow program at /workspace/hello
• an unprivileged flecha user

Docker Engine must be installed and running on the host.

Create the sandbox

From the repository root, run:

make sandbox

This builds the compiler and tools from the current working tree, including uncommitted files that are not excluded by .dockerignore. It then replaces the container named flecha-sandbox and starts the new container in the background. The host Git description is embedded in both tools, so their --version output identifies the checkout used to create the sandbox.

If the host has a Neovim configuration, the sandbox copies it from $XDG_CONFIG_HOME/nvim, or from $HOME/.config/nvim when XDG_CONFIG_HOME is unset. The copy is writable inside the disposable container, so plugin managers can maintain their lockfiles without changing the host configuration. Neovim’s data, cache, and downloaded plugins also remain inside the container. When the host directory does not exist, the sandbox uses a minimal configuration that enables Flecha filetype detection and syntax highlighting.

The repository is mounted read-only at its original absolute path. This lets a host configuration that points directly at editors/neovim keep using the current checkout. Compiler changes still require another make sandbox.

Set HOST_NVIM_CONFIG to use a different directory. Point it at a nonexistent directory to force the minimal configuration:

make sandbox HOST_NVIM_CONFIG=/path/to/nvim
make sandbox HOST_NVIM_CONFIG=/nonexistent

Re-run make sandbox whenever the compiler or editor plugin changes. Files created inside the old container are removed when it is replaced, so copy out anything you want to keep first.

Enter the sandbox

make enter-sandbox

This starts the container if necessary and opens an interactive login shell in /workspace. Try the installed tools with:

flecha --version
longbow --version
cd /workspace/hello
longbow check
longbow run
nvim src/main.fl

The container remains available after leaving the shell. Stop or remove it with normal Docker commands:

docker stop flecha-sandbox
docker rm -f flecha-sandbox

The image and container names can be changed without editing the Makefile:

make sandbox \
    SANDBOX_IMAGE=my-flecha:dev \
    SANDBOX_CONTAINER=my-flecha \
    HOST_NVIM_CONFIG=/path/to/nvim
make enter-sandbox SANDBOX_CONTAINER=my-flecha