dev_scripts: Install Poetry via pipx

We can no longer install Poetry via `pip`, since Debian Bookworm now
enforces PEP 668, meaning that both `pip install poetry` and `pip
install --user poetry` cannot work [1]. Since we use the same
installation steps for all of our dev environments, we need to find a
common way to install Poetry.

Poetry's website provides several ways to install Poetry [2]. Moreover,
it also has a special section with CI recommendations [3]. In this
section, it strongly suggests to install Poetry via `pipx`, instead of
the installer script that you download from the Internet.

Follow Poetry's suggestion to install it via `pipx` in CI environments,
with one minor change. Do not use `pipx ensurepath`, as that will
affect the `.bashrc` of the dev environment, which at some point in the
future may be mounted by the dev. Instead, set a PATH environment
variable that includes `~/.local/bin`.

[1]: https://github.com/freedomofpress/dangerzone/issues/351
[2]: https://python-poetry.org/docs/#installation
[3]: https://python-poetry.org/docs/#ci-recommendations

Fixes #351

dev_scripts/env.py

@@ -78,9 +78,18 @@ ARG DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends podman uidmap dh-python make \
-        build-essential fakeroot libqt5gui5 python3 python3-dev python3-venv \
+        build-essential fakeroot libqt5gui5 pipx python3 python3-dev \
-        python3-pip python3-stdeb python3-all \
+        python3-venv python3-stdeb python3-all \
     && rm -rf /var/lib/apt/lists/*
+# NOTE: `pipx install poetry` fails on Ubuntu Focal, when installed through APT. By
+# installing the latest version, we sidestep this issue.
+RUN bash -c 'if [[ "$(pipx --version)" < "1" ]]; then \
+                apt-get update \
+                && apt-get remove -y pipx \
+                && apt-get install -y --no-install-recommends python3-pip \
+                && pip install pipx \
+                && rm -rf /var/lib/apt/lists/*; \
+              else true; fi'
 RUN apt-get update \
     && apt-get install -y --no-install-recommends mupdf \
     && rm -rf /var/lib/apt/lists/*
@@ -88,7 +97,7 @@ RUN apt-get update \
 
 # FIXME: Install Poetry on Fedora via package manager.
 DOCKERFILE_BUILD_DEV_FEDORA_DEPS = r"""
-RUN dnf install -y rpm-build podman python3 make python3-pip qt5-qtbase-gui \
+RUN dnf install -y rpm-build podman python3 pipx make qt5-qtbase-gui \
     && dnf clean all
 
 # FIXME: Drop this fix after it's resolved upstream.
@@ -104,8 +113,6 @@ DOCKERFILE_BUILD_DEV = r"""FROM {distro}:{version}
 
 {install_deps}
 
-RUN python3 -m pip install poetry
-
 #########################################
 # Create a non-root user to run Dangerzone
 RUN adduser user
@@ -123,8 +130,14 @@ USER user
 WORKDIR /home/user
 VOLUME /home/user/dangerzone
 
+# Install Poetry under ~/.local/bin.
+# See https://github.com/freedomofpress/dangerzone/issues/351
+# FIXME: pipx install poetry does not work for Ubuntu Focal.
+ENV PATH="$PATH:/home/user/.local/bin"
+RUN pipx install poetry
+
 COPY pyproject.toml poetry.lock /home/user/dangerzone/
-RUN cd /home/user/dangerzone && poetry install
+RUN cd /home/user/dangerzone && poetry --no-ansi install
 """
 
 DOCKERFILE_BUILD_DEBIAN_DEPS = r"""
@@ -220,6 +233,10 @@ class Env:
         """Initialize an Env class based on some common parameters."""
         self.distro = distro
         self.version = version
+        # NOTE: We change "bullseye" to "bullseye-backports", since it contains `pipx`,
+        # which is not available through the original repos.
+        if self.distro == "debian" and self.version in ("bullseye", "11"):
+            self.version = "bullseye-backports"
 
         # Try to autodetect the runtime, if the user has not provided it.
         #