Update dockerfile to use poetry

docker/Dockerfile

@@ -6,26 +6,81 @@
 #    docker build -f docker/Dockerfile .
 #
 
+ARG PYTHON_VERSION=3.11
+
+###
+### Stage 0: generate requirements.txt
+###
+# We hardcode the use of Debian bookworm here because this could change upstream.
+FROM docker.io/library/python:${PYTHON_VERSION}-slim-bookworm as requirements
+
+# We install poetry in its own build stage to avoid its dependencies conflicting with
+# sygnal's dependencies.
+RUN --mount=type=cache,target=/root/.cache/pip \
+  pip install --user "poetry==1.3.2"
+
+WORKDIR /sygnal
+
+# Copy just what we need to run `poetry export`...
+COPY pyproject.toml poetry.lock /sygnal/
+
+# If specified, we won't verify the hashes of dependencies.
+# This is only needed if the hashes of dependencies cannot be checked for some
+# reason, such as when a git repository is used directly as a dependency.
+ARG TEST_ONLY_SKIP_DEP_HASH_VERIFICATION
+
+# If specified, we won't use the Poetry lockfile.
+# Instead, we'll just install what a regular `pip install` would from PyPI.
+ARG TEST_ONLY_IGNORE_POETRY_LOCKFILE
+
+# Export the dependencies, but only if we're actually going to use the Poetry lockfile.
+# Otherwise, just create an empty requirements file so that the Dockerfile can
+# proceed.
+RUN if [ -z "$TEST_ONLY_IGNORE_POETRY_LOCKFILE" ]; then \
+  /root/.local/bin/poetry export -o /sygnal/requirements.txt ${TEST_ONLY_SKIP_DEP_HASH_VERIFICATION:+--without-hashes}; \
+  else \
+  touch /sygnal/requirements.txt; \
+  fi
+
 ###
-### Stage 0: builder
+### Stage 1: builder
 ###
-FROM python:3.11-slim as builder
+FROM docker.io/library/python:${PYTHON_VERSION}-slim-bookworm as builder
 
-# Install git; Sygnal uses it to obtain the package version from the state of the
-# git repository.
-RUN apt-get update && apt-get install -y git
+# To speed up rebuilds, install all of the dependencies before we copy over
+# the whole sygnal project, so that this layer in the Docker cache can be
+# used while you develop on the source.
+#
+# This is aiming at installing the `[tool.poetry.depdendencies]` from pyproject.toml.
+COPY --from=requirements /sygnal/requirements.txt /sygnal/
+RUN --mount=type=cache,target=/root/.cache/pip \
+  pip install --prefix="/install" --no-deps --no-warn-script-location -r /sygnal/requirements.txt
 
-# install sygnal and all of the python deps to /install.
+# Copy over the rest of the sygnal source code.
+COPY sygnal /sygnal/sygnal/
+# ... and what we need to `pip install`.
+COPY pyproject.toml README.md /sygnal/
 
-COPY . /sygnal/
+# Repeat of earlier build argument declaration, as this is a new build stage.
+ARG TEST_ONLY_IGNORE_POETRY_LOCKFILE
 
-RUN pip install --prefix="/install" --no-warn-script-location /sygnal
+# Install the sygnal package itself.
+# If we have populated requirements.txt, we don't install any dependencies
+# as we should already have those from the previous `pip install` step.
+RUN --mount=type=cache,target=/sygnal/target,sharing=locked \
+  --mount=type=cache,target=${CARGO_HOME}/registry,sharing=locked \
+  if [ -z "$TEST_ONLY_IGNORE_POETRY_LOCKFILE" ]; then \
+  pip install --prefix="/install" --no-deps --no-warn-script-location /sygnal; \
+  else \
+  pip install --prefix="/install" --no-warn-script-location /sygnal; \
+  fi
 
 ###
-### Stage 1: runtime
+### Stage 2: runtime
 ###
 
-FROM python:3.11-slim
+FROM docker.io/library/python:${PYTHON_VERSION}-slim-bookworm
+
 COPY --from=builder /install /usr/local
 
 EXPOSE 5000/tcp