adding support for .d config files

config files in acccording .d folders are considered automatically, e.g.
for local config './west/config.d' respectively for global config
'~/.westconfig.d'

Author: thorsten-klein

src/west/configuration.py

@@ -68,15 +68,35 @@ def parse_key(dotted_name: str):
 
     @staticmethod
     def from_path(path: Path | None) -> '_InternalCF | None':
-        return _InternalCF(path) if path and path.exists() else None
+        config = _InternalCF(path) if path and path.exists() else None
+        if not config:
+            return None
+
+        # check if dropin configs exist (in according .d directory)
+        dropins_dir = Path(f'{path}.d')
+        if dropins_dir.exists():
+            # update config with values from dropin config files, whereby the
+            # dropin configs are applied in alphabetical order
+            for conf in sorted(dropins_dir.iterdir()):
+                config.cp.read(dropins_dir / conf, encoding='utf-8')
+            # finally overwrite with values from higher-prior actual config
+            config.cp.read(path, encoding='utf-8')
+        return config
 
     def __init__(self, path: Path):
         self.path = path
         self.cp = _configparser()
+        self._read(path)
+
+    def _read(self, path: Path):
         read_files = self.cp.read(path, encoding='utf-8')
         if len(read_files) != 1:
             raise FileNotFoundError(path)
 
+    def _write(self):
+        with open(self.path, 'w', encoding='utf-8') as f:
+            self.cp.write(f)
+
     def __contains__(self, option: str) -> bool:
         section, key = _InternalCF.parse_key(option)
 
@@ -110,8 +130,7 @@ def set(self, option: str, value: Any):
 
         self.cp[section][key] = value
 
-        with open(self.path, 'w', encoding='utf-8') as f:
-            self.cp.write(f)
+        self._write()
 
     def delete(self, option: str):
         section, key = _InternalCF.parse_key(option)
@@ -123,8 +142,7 @@ def delete(self, option: str):
         if not self.cp[section].items():
             del self.cp[section]
 
-        with open(self.path, 'w', encoding='utf-8') as f:
-            self.cp.write(f)
+        self._write()
 
 class ConfigFile(Enum):
     '''Types of west configuration file.

tests/test_config.py

@@ -6,6 +6,7 @@
 import os
 import pathlib
 import subprocess
+import textwrap
 from typing import Any
 
 import pytest
@@ -208,6 +209,40 @@ def test_local_creation():
     assert 'pytest' not in cfg(f=GLOBAL)
     assert cfg(f=LOCAL)['pytest']['key'] == 'val'
 
+TEST_CASES_CONFIG_D = [
+    # (flag, env_var)
+    ('', 'WEST_CONFIG_LOCAL'),
+    ('--local', 'WEST_CONFIG_LOCAL'),
+    ('--system', 'WEST_CONFIG_SYSTEM'),
+    ('--global', 'WEST_CONFIG_GLOBAL'),
+]
+
+@pytest.mark.parametrize("test_case", TEST_CASES_CONFIG_D)
+def test_config_d_local(test_case):
+    flag, env_var = test_case
+    config_path = os.environ[env_var]
+    config_d_dir = pathlib.Path(f'{config_path}.d')
+    config_d_dir.mkdir()
+
+    # write value in actual config file
+    cmd(f'config {flag} pytest.key val')
+    stdout = cmd(f'config {flag} pytest.key')
+    assert 'val' == stdout.rstrip()
+
+    # create a dropin config under .d
+    with open(config_d_dir / 'some-file', 'w') as conf:
+        conf.write(textwrap.dedent('''
+        [pytest]
+        key = from-.d
+        another-key = from-.d
+        '''))
+
+    # dropin config value is only used if option is not set in actual config
+    stdout = cmd(f'config {flag} pytest.key')
+    assert 'val' == stdout.rstrip()
+    stdout = cmd(f'config {flag} pytest.another-key')
+    assert 'from-.d' == stdout.rstrip()
+
 def test_local_creation_with_topdir():
     # Like test_local_creation, with a specified topdir.