plugins: add support for pyproject.toml projects (lp:#2008237) (#435)

Python projects move to pyproject.toml[0] instead of using setup.py so
add support to craft-parts so snaps can be build using the python
plugin.

[0] https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/

craft_parts/plugins/python_plugin.py

@@ -59,7 +59,7 @@ class PythonPlugin(Plugin):
     It can be used for python projects where you would want to do:
 
         - import python modules with a requirements.txt
-        - build a python project that has a setup.py
+        - build a python project that has a setup.py or pyproject.toml
         - install packages straight from pip
 
     This plugin uses the common plugin keywords as well as those for "sources".
@@ -153,7 +153,9 @@ def get_build_commands(self) -> List[str]:
             requirements_cmd = f"{pip} install {constraints} -U {requirements}"
             build_commands.append(requirements_cmd)
 
-        build_commands.append(f"[ -f setup.py ] && {pip} install {constraints} -U .")
+        build_commands.append(
+            f"[ -f setup.py ] || [ -f pyproject.toml ] && {pip} install {constraints} -U ."
+        )
 
         # Now fix shebangs.
         script_interpreter = self._get_script_interpreter()

tests/integration/plugins/test_python.py

@@ -60,6 +60,33 @@ def test_python_plugin(new_dir):
     assert primed_script.open().readline().rstrip() == "#!/usr/bin/env python3"
 
 
+def test_python_plugin_with_pyproject_toml(new_dir):
+    """Prime a simple python source."""
+    source_location = Path(__file__).parent / "test_python_pyproject_toml"
+
+    parts_yaml = textwrap.dedent(
+        f"""\
+        parts:
+          foo:
+            plugin: python
+            source: {source_location}
+        """
+    )
+    parts = yaml.safe_load(parts_yaml)
+
+    lf = LifecycleManager(
+        parts, application_name="test_python_pyproject_toml", cache_dir=new_dir
+    )
+    actions = lf.plan(Step.PRIME)
+
+    with lf.action_executor() as ctx:
+        ctx.execute(actions)
+
+    primed_script = Path(lf.project_info.prime_dir, "bin", "mytestpyprojecttoml")
+    assert primed_script.exists()
+    assert primed_script.open().readline().rstrip() == "#!/usr/bin/env python3"
+
+
 def test_python_plugin_symlink(new_dir):
     """Run in the standard scenario with no overrides."""
     parts_yaml = textwrap.dedent(

tests/integration/plugins/test_python_pyproject_toml/mytestpyprojecttoml/__init__.py

@@ -0,0 +1,2 @@
+def main():
+    print("it works also with pyproject.toml!")

tests/integration/plugins/test_python_pyproject_toml/pyproject.toml

@@ -0,0 +1,11 @@
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "plugin_test_pyproject_toml"
+description = "My package description"
+version = "0.0.1"
+
+[project.scripts]
+mytestpyprojecttoml = "mytestpyprojecttoml:main"

tests/unit/plugins/test_python_plugin.py

@@ -98,7 +98,7 @@ def test_get_build_commands(plugin, new_dir):
         f'"${{PARTS_PYTHON_INTERPRETER}}" -m venv ${{PARTS_PYTHON_VENV_ARGS}} "{new_dir}/parts/p1/install"',
         f'PARTS_PYTHON_VENV_INTERP_PATH="{new_dir}/parts/p1/install/bin/${{PARTS_PYTHON_INTERPRETER}}"',
         f"{new_dir}/parts/p1/install/bin/pip install  -U pip setuptools wheel",
-        f"[ -f setup.py ] && {new_dir}/parts/p1/install/bin/pip install  -U .",
+        f"[ -f setup.py ] || [ -f pyproject.toml ] && {new_dir}/parts/p1/install/bin/pip install  -U .",
     ] + get_build_commands(new_dir)
 
 
@@ -121,7 +121,7 @@ def test_get_build_commands_with_all_properties(new_dir):
         f'PARTS_PYTHON_VENV_INTERP_PATH="{new_dir}/parts/p1/install/bin/${{PARTS_PYTHON_INTERPRETER}}"',
         f"{new_dir}/parts/p1/install/bin/pip install -c 'constraints.txt' -U pip 'some-pkg; sys_platform != '\"'\"'win32'\"'\"''",
         f"{new_dir}/parts/p1/install/bin/pip install -c 'constraints.txt' -U -r 'requirements.txt'",
-        f"[ -f setup.py ] && {new_dir}/parts/p1/install/bin/pip install -c 'constraints.txt' -U .",
+        f"[ -f setup.py ] || [ -f pyproject.toml ] && {new_dir}/parts/p1/install/bin/pip install -c 'constraints.txt' -U .",
     ] + get_build_commands(new_dir)
 
 
@@ -173,7 +173,7 @@ def test_call_should_remove_symlinks(plugin, new_dir, mocker):
         f'"${{PARTS_PYTHON_INTERPRETER}}" -m venv ${{PARTS_PYTHON_VENV_ARGS}} "{new_dir}/parts/p1/install"',
         f'PARTS_PYTHON_VENV_INTERP_PATH="{new_dir}/parts/p1/install/bin/${{PARTS_PYTHON_INTERPRETER}}"',
         f"{new_dir}/parts/p1/install/bin/pip install  -U pip setuptools wheel",
-        f"[ -f setup.py ] && {new_dir}/parts/p1/install/bin/pip install  -U .",
+        f"[ -f setup.py ] || [ -f pyproject.toml ] && {new_dir}/parts/p1/install/bin/pip install  -U .",
         f'find "{new_dir}/parts/p1/install" -type f -executable -print0 | xargs -0 \\\n'
         f'    sed -i "1 s|^#\\!${{PARTS_PYTHON_VENV_INTERP_PATH}}.*$|#!/usr/bin/env ${{PARTS_PYTHON_INTERPRETER}}|"\n',
         f"echo Removing python symlinks in {new_dir}/parts/p1/install/bin\n"