ENH: support custom_target() installing a directory

Meson support custom_target() whose output is not a file but a
directory. Support these in meson-python mapping of installation paths
to wheel locations.

mesonpy/__init__.py

@@ -119,7 +119,7 @@ def _map_to_wheel(sources: Dict[str, Dict[str, Any]]) -> DefaultDict[str, List[T
                         f'{this!r} and {that!r}, a "pure: false" argument may be missing in meson.build. '
                         f'It is recommended to set it in "import(\'python\').find_installation()"')
 
-            if key == 'install_subdirs':
+            if key == 'install_subdirs' or key == 'targets' and os.path.isdir(src):
                 assert os.path.isdir(src)
                 exclude_files = {os.path.normpath(x) for x in target.get('exclude_files', [])}
                 exclude_dirs = {os.path.normpath(x) for x in target.get('exclude_dirs', [])}

mesonpy/_editable.py

@@ -245,7 +245,7 @@ def collect(install_plan: Dict[str, Dict[str, Any]]) -> Node:
         for src, target in data.items():
             path = pathlib.Path(target['destination'])
             if path.parts[0] in {'{py_platlib}', '{py_purelib}'}:
-                if key == 'install_subdirs' and os.path.isdir(src):
+                if key == 'install_subdirs' or key == 'targets' and os.path.isdir(src):
                     exclude_files = {os.path.normpath(x) for x in target.get('exclude_files', [])}
                     exclude_dirs = {os.path.normpath(x) for x in target.get('exclude_dirs', [])}
                     for entry in walk(src, exclude_files, exclude_dirs):

tests/packages/custom-target-dir/codegen.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+#
+# SPDX-FileCopyrightText: 2024 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+import os
+import sys
+
+
+outdir = os.path.join(sys.argv[1], 'generated')
+os.makedirs(outdir, exist_ok=True)
+
+for name in 'one.py', 'two.py':
+    with open(os.path.join(outdir, name), 'w'):
+        pass

tests/packages/custom-target-dir/meson.build

@@ -0,0 +1,14 @@
+# SPDX-FileCopyrightText: 2024 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project('custom-target-dir', version: '1.0.0')
+
+py = import('python').find_installation()
+
+custom_target(
+    command: ['codegen.py', '@OUTDIR@'],
+    output: 'generated',
+    install: true,
+    install_dir: py.get_install_dir() / 'package',
+)

tests/packages/custom-target-dir/pyproject.toml

@@ -0,0 +1,7 @@
+# SPDX-FileCopyrightText: 2024 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[build-system]
+build-backend = 'mesonpy'
+requires = ['meson-python']

tests/test_editable.py

@@ -226,3 +226,14 @@ def test_editable_pkgutils_walk_packages(package_complex, tmp_path):
         # remove hooks
         del sys.meta_path[0]
         del sys.path_hooks[0]
+
+
+def test_custom_target_install_dir(package_custom_target_dir, tmp_path):
+    mesonpy.Project(package_custom_target_dir, tmp_path)
+    finder = _editable.MesonpyMetaFinder({'package'}, os.fspath(tmp_path), ['ninja'])
+    try:
+        sys.meta_path.insert(0, finder)
+        import package.generated.one
+        import package.generated.two  # noqa: F401
+    finally:
+        del sys.meta_path[0]

tests/test_wheel.py

@@ -350,3 +350,15 @@ def test_encoding(package_encoding, tmp_path):
         'encoding-1.0.0.dist-info/WHEEL',
         'テスト.py',
     }
+
+
+def test_custom_target_install_dir(package_custom_target_dir, tmp_path):
+    filename = mesonpy.build_wheel(tmp_path)
+    artifact = wheel.wheelfile.WheelFile(tmp_path / filename)
+    assert wheel_contents(artifact) == {
+        'custom_target_dir-1.0.0.dist-info/METADATA',
+        'custom_target_dir-1.0.0.dist-info/RECORD',
+        'custom_target_dir-1.0.0.dist-info/WHEEL',
+        'package/generated/one.py',
+        'package/generated/two.py',
+    }