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Languages and toolchains

A working directory has exactly one language at a time, recorded alongside its content and reflected in the solution file's own extension — data/solution.py, data/solution.cpp, and so on. Switching language renames the file.

cg puzzle set-language C++
cg contribution set-language Python3

Puzzles remember every language you've used

CodinGame stores your most recent source per language for a puzzle. So switching a puzzle's language is reversible: anything you previously wrote in the target language comes back, and a language you've never used gets a placeholder.

cg puzzle set-language refuses if the solution holds work the server doesn't have — submit it first, or pass --force to discard it. It needs the network even though it only changes local state, because restoring your previous code means fetching it.

Contributions remember exactly one

A contribution stores a single reference solution with no per-language history. So cg contribution set-language is destructive by design: it replaces the solution with a starter stub, and the next cg contribution push overwrites the last durable copy. There is nothing to switch back to. It refuses unless the current solution is still the stub cg generated, and --force is required to discard real work — save it somewhere outside the working directory first.

There's a wrinkle worth knowing: only Python3 ships a starter stub that actually passes the seeded test cases, so switching to any other language leaves the solution file empty. That's required, not a shortfall. updateContribution skips solution validation entirely when the solution is null, but validates any non-null one against every test case — so a comment-only placeholder in another language would fail validation and block your push.

Running and building locally

cg puzzle play          # run against downloaded test cases, no network at all
cg contribution play    # same, against data/tests/
cg puzzle build         # compile without running (no-op for interpreted languages)

play builds first when the language needs it, so build is only for compiling without running, or for warming a cold container image before you start.

Local comparison of your output against the expected output is exactly as strict as CodinGame's — everything compared byte-for-byte, except a difference of one trailing newline in either direction. That equivalence is measured, not assumed, and the measurements are in output comparison. It matters because a local pass that fails on submission is the worst outcome the runner can produce.

Compiled languages run in Docker

You do not need a local toolchain. For a compiled language, cg builds and runs inside a container:

  • One long-lived container per (working directory × language). Change language and the old one is replaced, not orphaned.
  • Your working directory is bind-mounted read-only; all build artifacts live inside the container, so nothing appears in data/ that you didn't put there.
  • Images are content-addressed, so an unchanged source rebuilds in roughly no time.
  • The image definition is a Dockerfile you can edit, in a shared per-user location, so tweaking a language's toolchain once applies everywhere.
cg docker clean   # tear down every container and image this tool created

That's always safe. No user work ever lives in a cg-managed container or image — the source is mounted from disk and artifacts are disposable — so there's no prompt and no --force.

Which languages are supported

Every language CodinGame accepts can be selected, and the client knows each one's file extension and comment syntax. How much more than that works varies:

  • Python3 — fully supported: local run, local debug (in-process, breakpoints in your solution).
  • C++ — fully supported via Docker: build, run, and attach-style debugging with gdbserver.
  • Everything else — selectable and submittable, with local execution depending on whether a toolchain module exists for it.

Adding a language is a self-contained module under codingame_tools/language/languages/; the registry discovers it automatically.