README.md

Elixir SDK runtime (build-only)

This is the Elixir module runtime. New Elixir modules reference it as their runtime (github.com/dagger/elixir-sdk/runtime); the root Dang module (elixir-sdk.dang) sets it via targetRuntime.

It is written in Dang (main.dang), so the engine runs its dispatch (moduleRuntime / codegen) natively in-process — there is no runtime container for the dispatcher itself. The actual Elixir build still runs in an elixir:*-alpine container.

What it does

It only fetches dependencies, compiles, and sets the entrypoint for an Elixir module from its committed sources — it does not generate code.

moduleRuntime mounts the module, runs mix deps.get --only prod → mix deps.compile → mix compile, and returns a container whose entrypoint is mix dagger.entrypoint.invoke <ModuleName>.

Modules are self-contained: the Elixir SDK is vendored as source under <module>/dagger_sdk/ and mix.exs depends on it by path, so mix deps.get only fetches third-party dependencies.

Before compiling, moduleRuntime checks that dagger_sdk/mix.exs exists and is non-empty, failing early with an actionable error if dagger generate was never run or its output was not committed. Without that check, mix deps.get fails on the unresolvable path dependency with an error that never mentions dagger generate.

What owns code generation instead

Code generation lives in this repository's root Dang module (elixir-sdk.dang / mod.dang) and runs at dagger generate time. Modules commit the generated files, so the engine skips codegen at module load and this runtime never regenerates them.

codegen here is an intentional no-op (it returns the module source unchanged): the SDK runtime contract still includes it, but generation is owned by generate.

Keeping names in sync

toElixirApplicationName / toElixirModuleName in main.dang derive the entrypoint's module name from the Dagger module name at call time. helpers/render-template/main.go derives the defmodule name from the same input at init time. The two implementations must stay identical — helpers/render-template/main_test.go pins the cases where a general-purpose case library would disagree (HTTPServer, foo2bar).