Allow resolving package metadata even when libsystemd is not available

.github/workflows/resolver.yml

@@ -0,0 +1,78 @@
+---
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+name: Resolver compatibility
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  linux-build:
+    runs-on: ubuntu-latest
+    name: Linux build and wheel smoke
+    steps:
+      - name: Repository checkout
+        uses: actions/checkout@v4
+
+      - name: Configure Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install system and Python build dependencies
+        run: |
+          sudo apt -y update
+          sudo apt -y install gcc libsystemd-dev pkg-config
+          python -m pip install -U pip build
+
+      - name: Build artifacts and wheel
+        run: |
+          python -m build --sdist --wheel
+          python -m pip wheel --use-pep517 --no-deps .
+
+  macos-metadata-lock:
+    runs-on: macos-14
+    name: macOS metadata and lock smoke
+    steps:
+      - name: Repository checkout
+        uses: actions/checkout@v4
+
+      - name: Configure Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install Python packaging tools
+        run: python -m pip install -U pip build
+
+      - name: Setup uv
+        uses: astral-sh/setup-uv@v6
+
+      - name: sdist build should not require libsystemd
+        run: python -m build --sdist
+
+      - name: PEP 517 wheel build should not hard-fail without libsystemd
+        run: python -m pip wheel --use-pep517 --no-deps .
+
+      - name: uv lock smoke for linux marker dependency
+        run: |
+          mkdir -p /tmp/uv-lock-smoke
+          cat > /tmp/uv-lock-smoke/pyproject.toml <<'EOF'
+          [project]
+          name = "uv-lock-smoke"
+          version = "0.0.0"
+          dependencies = [
+            "systemd-python; sys_platform == 'linux'",
+          ]
+
+          [tool.uv.sources]
+          systemd-python = { path = "${{ github.workspace }}" }
+          EOF
+          cd /tmp/uv-lock-smoke
+          uv lock
+          grep -q 'name = "systemd-python"' uv.lock

meson.build

@@ -15,14 +15,23 @@ python_dep = python.dependency()
 
 fs = import('fs')
 
-libsystemd_dep = dependency('libsystemd')
+libsystemd_dep = dependency('libsystemd', required: false)
+build_extensions = host_machine.system() == 'linux' and libsystemd_dep.found()
 
-add_project_arguments(
-        '-D_GNU_SOURCE=1',
-        '-DPACKAGE_VERSION="@0@"'.format(meson.project_version()),
-        '-DLIBSYSTEMD_VERSION=@0@'.format(libsystemd_dep.version()),
-        language : 'c',
-)
+if host_machine.system() != 'linux'
+        warning('libsystemd bindings are skipped on non-Linux platforms. This build provides package metadata and pure Python files only.')
+elif not libsystemd_dep.found()
+        warning('libsystemd development files were not found; native extension modules will not be built. Install libsystemd dev packages for full functionality.')
+endif
+
+if build_extensions
+        add_project_arguments(
+                '-D_GNU_SOURCE=1',
+                '-DPACKAGE_VERSION="@0@"'.format(meson.project_version()),
+                '-DLIBSYSTEMD_VERSION=@0@'.format(libsystemd_dep.version()),
+                language : 'c',
+        )
+endif
 
 update_constants_py = files('update-constants.py')
 
@@ -39,7 +48,9 @@ test(
         env: { 'PYTHONPATH': meson.current_build_dir() / 'src' },
 )
 
-alias_target('update-constants', update_constants)
+if build_extensions
+        alias_target('update-constants', update_constants)
+endif
 
 # Docs
 sphinx_build = find_program('sphinx-build', disabler: true, required: get_option('docs'))

src/systemd/daemon.py

@@ -2,18 +2,25 @@
 
 from socket import AF_UNSPEC as _AF_UNSPEC
 
-from ._daemon import (__version__,
-                      booted,
-                      notify,
-                      _listen_fds,
-                      _listen_fds_with_names,
-                      _is_fifo,
-                      _is_socket,
-                      _is_socket_inet,
-                      _is_socket_sockaddr,
-                      _is_socket_unix,
-                      _is_mq,
-                      LISTEN_FDS_START)
+try:
+    from ._daemon import (__version__,
+                          booted,
+                          notify,
+                          _listen_fds,
+                          _listen_fds_with_names,
+                          _is_fifo,
+                          _is_socket,
+                          _is_socket_inet,
+                          _is_socket_sockaddr,
+                          _is_socket_unix,
+                          _is_mq,
+                          LISTEN_FDS_START)
+except ModuleNotFoundError as e:
+    raise ImportError(
+        "systemd.daemon requires native libsystemd bindings that are not available "
+        "in this build. Build/install on Linux with libsystemd development files "
+        "to enable this module."
+    ) from e
 
 def _convert_fileobj(fileobj):
     try:

src/systemd/journal.py

@@ -9,13 +9,20 @@
 from syslog import (LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR,
                     LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG)
 
-from ._journal import __version__, sendv, stream_fd
-from ._reader import (_Reader, NOP, APPEND, INVALIDATE,
-                      LOCAL_ONLY, RUNTIME_ONLY,
-                      SYSTEM, SYSTEM_ONLY, CURRENT_USER,
-                      OS_ROOT,
-                      _get_catalog, Monotonic)
-from . import id128 as _id128
+try:
+    from ._journal import __version__, sendv, stream_fd
+    from ._reader import (_Reader, NOP, APPEND, INVALIDATE,
+                          LOCAL_ONLY, RUNTIME_ONLY,
+                          SYSTEM, SYSTEM_ONLY, CURRENT_USER,
+                          OS_ROOT,
+                          _get_catalog, Monotonic)
+    from . import id128 as _id128
+except ModuleNotFoundError as e:
+    raise ImportError(
+        "systemd.journal requires native libsystemd bindings that are not "
+        "available in this build. Build/install on Linux with libsystemd "
+        "development files to enable this module."
+    ) from e
 
 
 def _convert_monotonic(m):

src/systemd/meson.build

@@ -1,49 +1,51 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
-# Build _journal extension module
-python.extension_module(
-        '_journal',
-        ['_journal.c', 'pyutil.c'],
-        dependencies: [libsystemd_dep],
-        install: true,
-        subdir: 'systemd',
-)
+if build_extensions
+        # Build _journal extension module
+        python.extension_module(
+                '_journal',
+                ['_journal.c', 'pyutil.c'],
+                dependencies: [libsystemd_dep],
+                install: true,
+                subdir: 'systemd',
+        )
 
-# Build _reader extension module
-python.extension_module(
-        '_reader',
-        ['_reader.c', 'pyutil.c', 'strv.c'],
-        dependencies: [libsystemd_dep],
-        install: true,
-        subdir: 'systemd',
-)
+        # Build _reader extension module
+        python.extension_module(
+                '_reader',
+                ['_reader.c', 'pyutil.c', 'strv.c'],
+                dependencies: [libsystemd_dep],
+                install: true,
+                subdir: 'systemd',
+        )
 
-# Build _daemon extension module
-python.extension_module(
-        '_daemon',
-        ['_daemon.c', 'pyutil.c', 'util.c'],
-        dependencies: [libsystemd_dep],
-        install: true,
-        subdir: 'systemd',
-)
+        # Build _daemon extension module
+        python.extension_module(
+                '_daemon',
+                ['_daemon.c', 'pyutil.c', 'util.c'],
+                dependencies: [libsystemd_dep],
+                install: true,
+                subdir: 'systemd',
+        )
 
-# Build id128 extension module
-python.extension_module(
-        'id128',
-        ['id128.c', 'pyutil.c'],
-        dependencies: [libsystemd_dep],
-        install: true,
-        subdir: 'systemd',
-)
+        # Build id128 extension module
+        python.extension_module(
+                'id128',
+                ['id128.c', 'pyutil.c'],
+                dependencies: [libsystemd_dep],
+                install: true,
+                subdir: 'systemd',
+        )
 
-# Build login extension module
-python.extension_module(
-        'login',
-        ['login.c', 'pyutil.c', 'strv.c'],
-        dependencies: [libsystemd_dep],
-        install: true,
-        subdir: 'systemd',
-)
+        # Build login extension module
+        python.extension_module(
+                'login',
+                ['login.c', 'pyutil.c', 'strv.c'],
+                dependencies: [libsystemd_dep],
+                install: true,
+                subdir: 'systemd',
+        )
+endif
 
 # Install Python modules
 py_files = files(
@@ -67,15 +69,17 @@ python.install_sources(
         subdir: 'systemd/test',
 )
 
-# The 'update-constants' target
-include_dir = libsystemd_dep.get_variable(pkgconfig: 'includedir')
+if build_extensions
+        # The 'update-constants' target
+        include_dir = libsystemd_dep.get_variable(pkgconfig: 'includedir')
 
-update_constants = custom_target(
-        output: 'update-constants',
-        command: [
-                update_constants_py,
-                meson.current_source_dir() / 'id128-constants.h',
-                meson.project_source_root() / 'docs/id128.rst',
-                meson.current_source_dir() / 'id128-defines.h',
-                include_dir / 'systemd/sd-messages.h',
-        ])
+        update_constants = custom_target(
+                output: 'update-constants',
+                command: [
+                        update_constants_py,
+                        meson.current_source_dir() / 'id128-constants.h',
+                        meson.project_source_root() / 'docs/id128.rst',
+                        meson.current_source_dir() / 'id128-defines.h',
+                        include_dir / 'systemd/sd-messages.h',
+                ])
+endif