chore: initial commit

Dockerfile

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+ARG NIX_TAG="latest"
+
+FROM nixos/nix:$NIX_TAG
+
+COPY entrypoint.sh /usr/local/bin/
+
+ENTRYPOINT ["/bin/sh", "/usr/local/bin/entrypoint.sh"]

README.md

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+# Gitlab Nix Docker Image
+Image: [`technofab/nix-gitlab-ci:latest`](https://hub.docker.com/repository/docker/technofab/nix-gitlab-ci/general)
+
+This simple image tries to start a Nix devShell from a flake.nix in the repository.
+It uses the devShell named `ci` (optionally just link to the default shell, see below).
+
+```nix
+...
+rec {
+    default = devenv.lib.mkShell {};
+    ci = default;
+};
+...
+```

entrypoint.sh

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+#!/bin/sh
+set -e
+
+cd "$CI_PROJECT_DIR"
+
+echo "Trying to activate flake's CI shell..."
+{
+  nix --extra-experimental-features "flakes nix-command" develop .#ci --impure --command "bash" >/dev/null
+} || {
+  echo "nix develop failed, falling back to normal shell..."
+  eval "bash"
+}