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

docs/reference/plugins/_python_common.rst

@@ -0,0 +1,17 @@
+
+Dependencies
+------------
+
+Whether the Python interpreter needs to be included in the snap depends on its
+``confinement``. Specifically:
+
+- Projects with ``strict`` or ``devmode`` confinement can safely use the base
+  snap's interpreter, so they typically do **not** need to include Python.
+- Projects with ``classic`` confinement **cannot** use the base snap's
+  interpreter and thus must always bundle it (typically via ``stage-packages``).
+- In both cases, a specific/custom Python installation can always be included
+  in the snap. This can be useful, for example, when using a different Python
+  version or building an interpreter with custom flags.
+
+Snapcraft will prefer an included interpreter over the base's, even for projects
+with ``strict`` and ``devmode`` confinement.

docs/reference/plugins/poetry_plugin.rst

@@ -0,0 +1,7 @@
+.. include:: /common/craft-parts/reference/plugins/poetry_plugin.rst
+   :end-before: .. _poetry-details-begin:
+
+.. include:: _python_common.rst
+
+.. include:: /common/craft-parts/reference/plugins/poetry_plugin.rst
+   :start-after: .. _poetry-details-end:

docs/reference/plugins/python_plugin.rst

@@ -2,22 +2,7 @@
 .. include:: /common/craft-parts/reference/plugins/python_plugin.rst
    :end-before: .. _python-details-begin:
 
-Dependencies
-------------
-
-Whether the Python interpreter needs to be included in the snap depends on its
-``confinement``. Specifically:
-
-- Projects with ``strict`` or ``devmode`` confinement can safely use the base
-  snap's interpreter, so they typically do **not** need to include Python.
-- Projects with ``classic`` confinement **cannot** use the base snap's
-  interpreter and thus must always bundle it (typically via ``stage-packages``).
-- In both cases, a specific/custom Python installation can always be included
-  in the snap. This can be useful, for example, when using a different Python
-  version or building an interpreter with custom flags.
-
-Snapcraft will prefer an included interpreter over the base's, even for projects
-with ``strict`` and ``devmode`` confinement.
+.. include:: _python_common.rst
 
 .. include:: /common/craft-parts/reference/plugins/python_plugin.rst
    :start-after: .. _python-details-end:

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/__init__.py

@@ -22,6 +22,7 @@
 from .flutter_plugin import FlutterPlugin
 from .kernel_plugin import KernelPlugin
 from .matter_sdk_plugin import MatterSdkPlugin
+from .poetry_plugin import PoetryPlugin
 from .python_plugin import PythonPlugin
 from .register import get_plugins, register
 
@@ -31,6 +32,7 @@
     "FlutterPlugin",
     "MatterSdkPlugin",
     "KernelPlugin",
+    "PoetryPlugin",
     "PythonPlugin",
     "get_plugins",
     "register",

snapcraft/parts/plugins/poetry_plugin.py

@@ -0,0 +1,30 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 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/>.
+
+"""The Snapcraft Poetry plugin."""
+
+from craft_parts.plugins import poetry_plugin
+from overrides import override
+
+from snapcraft.parts.plugins import python_common
+
+
+class PoetryPlugin(poetry_plugin.PoetryPlugin):
+    """A Poetry plugin for Snapcraft."""
+
+    @override
+    def _get_system_python_interpreter(self) -> str | None:
+        return python_common.get_system_interpreter(self._part_info)

snapcraft/parts/plugins/python_common.py

@@ -0,0 +1,96 @@
+# -*- 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 functionality for Python-based plugins.
+
+This plugin extends Craft-parts' vanilla Python plugin to properly
+set the Python interpreter according to the Snapcraft base and
+confinement parameters.
+"""
+
+import logging
+from pathlib import Path
+
+from craft_parts import PartInfo, StepInfo, errors
+
+logger = logging.getLogger(__name__)
+
+
+_CONFINED_PYTHON_PATH = {
+    "core22": "/usr/bin/python3.10",
+    "core24": "/usr/bin/python3.12",
+}
+
+
+def get_system_interpreter(part_info: PartInfo) -> str | None:
+    """Obtain the path to the system-provided python interpreter.
+
+    :param part_info: The info of the part that is being built.
+    """
+    base = part_info.project_base
+    confinement = part_info.confinement
+
+    if confinement == "classic" or base == "bare":
+        # classic snaps, and snaps without bases, must always provision Python
+        interpreter = None
+    else:
+        # otherwise, we should always know which Python is present on the
+        # base. If this fails on a new base, update _CONFINED_PYTHON_PATH
+        interpreter = _CONFINED_PYTHON_PATH.get(base)
+        if interpreter is None:
+            brief = f"Don't know which interpreter to use for base {base}."
+            resolution = "Please contact the Snapcraft team."
+            raise errors.PartsError(brief=brief, resolution=resolution)
+
+    logger.debug(
+        "Using python interpreter '%s' for base '%s', confinement '%s'",
+        interpreter,
+        base,
+        confinement,
+    )
+    return interpreter
+
+
+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/parts/plugins/python_plugin.py

@@ -16,84 +16,17 @@
 
 """The Snapcraft Python plugin."""
 
-import logging
-from pathlib import Path
 from typing import Optional
 
-from craft_parts import StepInfo, errors
 from craft_parts.plugins import python_plugin
 from overrides import override
 
-logger = logging.getLogger(__name__)
-
-
-_CONFINED_PYTHON_PATH = {
-    "core22": "/usr/bin/python3.10",
-    "core24": "/usr/bin/python3.12",
-}
+from snapcraft.parts.plugins import python_common
 
 
 class PythonPlugin(python_plugin.PythonPlugin):
-    """A Python plugin for Snapcraft.
-
-    This plugin extends Craft-parts' vanilla Python plugin to properly
-    set the Python interpreter according to the Snapcraft base and
-    confinement parameters.
-    """
+    """A Python plugin for Snapcraft."""
 
     @override
     def _get_system_python_interpreter(self) -> Optional[str]:
-        base = self._part_info.project_base
-        confinement = self._part_info.confinement
-
-        if confinement == "classic" or base == "bare":
-            # classic snaps, and snaps without bases, must always provision Python
-            interpreter = None
-        else:
-            # otherwise, we should always know which Python is present on the
-            # base. If this fails on a new base, update _CONFINED_PYTHON_PATH
-            interpreter = _CONFINED_PYTHON_PATH.get(base)
-            if interpreter is None:
-                brief = f"Don't know which interpreter to use for base {base}."
-                resolution = "Please contact the Snapcraft team."
-                raise errors.PartsError(brief=brief, resolution=resolution)
-
-        logger.debug(
-            "Using python interpreter '%s' for base '%s', confinement '%s'",
-            interpreter,
-            base,
-            confinement,
-        )
-        return interpreter
-
-    @classmethod
-    def post_prime(cls, 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)
+        return python_common.get_system_interpreter(self._part_info)

snapcraft/parts/plugins/register.py

@@ -24,6 +24,7 @@
 from .flutter_plugin import FlutterPlugin
 from .kernel_plugin import KernelPlugin
 from .matter_sdk_plugin import MatterSdkPlugin
+from .poetry_plugin import PoetryPlugin
 from .python_plugin import PythonPlugin
 
 
@@ -38,6 +39,7 @@ def get_plugins(core22: bool) -> dict[str, PluginType]:
         "flutter": FlutterPlugin,
         "python": PythonPlugin,
         "matter-sdk": MatterSdkPlugin,
+        "poetry": PoetryPlugin,
     }
 
     if core22:

snapcraft/services/lifecycle.py

@@ -86,16 +86,16 @@ def setup(self) -> None:
     @overrides
     def post_prime(self, step_info: StepInfo) -> bool:
         """Run post-prime parts steps for Snapcraft."""
-        from snapcraft.parts import plugins
+        from snapcraft.parts.plugins import python_common
 
         project = cast(models.Project, self._project)
 
         part_name = step_info.part_name
         plugin_name = project.parts[part_name]["plugin"]
 
         # Handle plugin-specific prime fixes
-        if plugin_name == "python":
-            plugins.PythonPlugin.post_prime(step_info)
+        if plugin_name in ("python", "poetry"):
+            python_common.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-poetry:
+    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: poetry-hello
+version: "1.0"
+summary: simple python application
+description: build a python application using core22
+base: core22
+confinement: strict
+
+apps:
+  poetry-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")