1 files changed, 64 insertions, 0 deletions
diff --git a/.ci/scripts/prepare_old_deps.sh b/.ci/scripts/prepare_old_deps.sh
new file mode 100755
index 0000000000..7e4f060b17
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+++ b/.ci/scripts/prepare_old_deps.sh
@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+# this script is run by GitHub Actions in a plain `focal` container; it
+# - installs the minimal system requirements, and poetry;
+# - patches the project definition file to refer to old versions only;
+# - creates a venv with these old versions using poetry; and finally
+# - invokes `trial` to run the tests with old deps.
+
+set -ex
+
+# Prevent virtualenv from auto-updating pip to an incompatible version
+export VIRTUALENV_NO_DOWNLOAD=1
+
+# TODO: in the future, we could use an implementation of
+#   https://github.com/python-poetry/poetry/issues/3527
+#   https://github.com/pypa/pip/issues/8085
+# to select the lowest possible versions, rather than resorting to this sed script.
+
+# Patch the project definitions in-place:
+# - Replace all lower and tilde bounds with exact bounds
+# - Replace all caret bounds---but not the one that defines the supported Python version!
+# - Delete all lines referring to psycopg2 --- so no testing of postgres support.
+# - Use pyopenssl 17.0, which is the oldest version that works with
+#   a `cryptography` compiled against OpenSSL 1.1.
+# - Omit systemd: we're not logging to journal here.
+
+sed -i \
+   -e "s/[~>]=/==/g" \
+   -e '/^python = "^/!s/\^/==/g' \
+   -e "/psycopg2/d" \
+   -e 's/pyOpenSSL = "==16.0.0"/pyOpenSSL = "==17.0.0"/' \
+   -e '/systemd/d' \
+   pyproject.toml
+
+# Use poetry to do the installation. This ensures that the versions are all mutually
+# compatible (as far the package metadata declares, anyway); pip's package resolver
+# is more lax.
+#
+# Rather than `poetry install --no-dev`, we drop all dev dependencies from the
+# toml file. This means we don't have to ensure compatibility between old deps and
+# dev tools.
+
+pip install toml wheel
+
+REMOVE_DEV_DEPENDENCIES="
+import toml
+with open('pyproject.toml', 'r') as f:
+    data = toml.loads(f.read())
+
+del data['tool']['poetry']['dev-dependencies']
+
+with open('pyproject.toml', 'w') as f:
+    toml.dump(data, f)
+"
+python3 -c "$REMOVE_DEV_DEPENDENCIES"
+
+pip install poetry==1.2.0
+poetry lock
+
+echo "::group::Patched pyproject.toml"
+cat pyproject.toml
+echo "::endgroup::"
+echo "::group::Lockfile after patch"
+cat poetry.lock
+echo "::endgroup::"