feat: add Snapcraft-specific Poetry plugin

The plugin has the same behavior and restrictions as the Python plugin with
regards to base-dependent behavior, symlink handling, etc.

Therefore, this common behavior is extracted into a new "python_common" module,
used by both plugins. This approach is also taken for the reference docs - the
requirement of staging a Python interpreter (or not) is the same for both
plugins.

Enabled for core22 and core24.

Fixes #5025

snapcraft/application.py

@@ -135,9 +135,6 @@ def _register_default_plugins(self) -> None:
         """Register per application plugins when initializing."""
         super()._register_default_plugins()
 
-        # poetry plugin needs integration work, see #5025
-        craft_parts.plugins.unregister("poetry")
-
         if self._known_core24:
             # dotnet is disabled for core24 and newer because it is pending a rewrite
             craft_parts.plugins.unregister("dotnet")

snapcraft/parts/plugins/python_common.py

@@ -0,0 +1,55 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 2023-2024 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Common functions for Python-based Snapcraft plugins."""
+import logging
+from pathlib import Path
+
+from craft_parts import StepInfo
+
+logger = logging.getLogger(__name__)
+
+
+def post_prime(step_info: StepInfo) -> None:
+    """Perform Python-specific actions right before packing."""
+    base = step_info.project_base
+
+    if base in ("core20", "core22"):
+        # Only fix pyvenv.cfg on core24+ snaps
+        return
+
+    root_path: Path = step_info.prime_dir
+
+    pyvenv = root_path / "pyvenv.cfg"
+    if not pyvenv.is_file():
+        return
+
+    snap_path = Path(f"/snap/{step_info.project_name}/current")
+    new_home = f"home = {snap_path}"
+
+    candidates = (
+        step_info.part_install_dir,
+        step_info.stage_dir,
+    )
+
+    old_contents = contents = pyvenv.read_text()
+    for candidate in candidates:
+        old_home = f"home = {candidate}"
+        contents = contents.replace(old_home, new_home)
+
+    if old_contents != contents:
+        logger.debug("Updating pyvenv.cfg to:\n%s", contents)
+        pyvenv.write_text(contents)

snapcraft/services/lifecycle.py

@@ -94,7 +94,7 @@ def post_prime(self, step_info: StepInfo) -> bool:
         plugin_name = project.parts[part_name]["plugin"]
 
         # Handle plugin-specific prime fixes
-        if plugin_name == "python":
+        if plugin_name in ("python", "poetry"):
             plugins.PythonPlugin.post_prime(step_info)
 
         # Handle patch-elf

tests/spread/core24/python-hello/poetry/snap/snapcraft.yaml

@@ -0,0 +1,14 @@
+name: python-hello-poetry
+version: "1.0"
+summary: simple python application
+description: build a python application using core24
+base: core24
+confinement: strict
+
+apps:
+  python-hello-strict:
+    command: bin/hello
+parts:
+  hello:
+    plugin: poetry
+    source: src

tests/spread/core24/python-hello/poetry/src/pyproject.toml

@@ -0,0 +1,18 @@
+[tool.poetry]
+name = "hello"
+version = "0.1.0"
+description = ""
+authors = ["Your Name <you@example.com>"]
+
+[tool.poetry.dependencies]
+python = "^3.10"
+black = "^24.8.0"
+
+[tool.poetry.dev-dependencies]
+
+[build-system]
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"
+
+[tool.poetry.scripts]
+hello = "hello:main"

tests/spread/core24/python-hello/task.yaml

@@ -8,6 +8,7 @@ systems:
 environment:
   PARAM/strict: ""
   PARAM/classic: "--classic"
+  PARAM/poetry: ""
 
 restore: |
   cd ./"${SPREAD_VARIANT}"

tests/spread/plugins/craft-parts/build-and-run-hello/poetry-hello/snap/snapcraft.yaml

@@ -0,0 +1,15 @@
+name: python-hello
+version: "1.0"
+summary: simple python application
+description: build a python application using core22
+base: core22
+confinement: strict
+
+apps:
+  python-hello:
+    command: bin/hello
+
+parts:
+  hello:
+    plugin: poetry
+    source: src

tests/spread/plugins/craft-parts/build-and-run-hello/poetry-hello/src/hello/__init__.py

@@ -0,0 +1,2 @@
+def main():
+    print("hello world")

tests/spread/plugins/craft-parts/build-and-run-hello/poetry-hello/src/pyproject.toml

@@ -0,0 +1,18 @@
+[tool.poetry]
+name = "hello"
+version = "0.1.0"
+description = ""
+authors = ["Your Name <you@example.com>"]
+
+[tool.poetry.dependencies]
+python = "^3.10"
+black = "^24.8.0"
+
+[tool.poetry.dev-dependencies]
+
+[build-system]
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"
+
+[tool.poetry.scripts]
+hello = "hello:main"

tests/spread/plugins/craft-parts/build-and-run-hello/task.yaml

@@ -8,6 +8,7 @@ environment:
   SNAP/colcon_ros2_wrapper: colcon-ros2-wrapper
   SNAP/flutter: flutter-hello
   SNAP/python: python-hello
+  SNAP/poetry: poetry-hello
   SNAP/qmake: qmake-hello
   SNAP/maven: maven-hello
   SNAP/dotnet: dotnet-hello

tests/unit/parts/plugins/test_python_plugin.py

@@ -19,7 +19,7 @@
 import pytest
 from craft_parts import Part, PartInfo, ProjectInfo, Step, StepInfo, errors
 
-from snapcraft.parts.plugins import PythonPlugin
+from snapcraft.parts.plugins import PythonPlugin, python_common
 
 
 @pytest.fixture
@@ -224,7 +224,7 @@ def test_fix_pyvenv(new_dir, home_attr):
 
     step_info = StepInfo(part_info, Step.PRIME)
 
-    PythonPlugin.post_prime(step_info)
+    python_common.post_prime(step_info)
 
     new_contents = pyvenv.read_text()
     assert "home = /snap/test-snap/current/usr/bin" in new_contents