configuration: create missing config files

Add a helper to create the configuration file if it doesn't already
exist, and call it from update_config().

Add test cases for the API-level changes, which we can do now that we
can patch out all the config file locations.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

src/west/commands/config.py

@@ -121,4 +121,11 @@ class Config(WestCommand):
             if configfile == ConfigFile.ALL:
                 # No file given, thus writing defaults to LOCAL
                 configfile = ConfigFile.LOCAL
-            configuration.update_config(section, key, args.value, configfile)
+            try:
+                configuration.update_config(section, key, args.value,
+                                            configfile)
+            except PermissionError as pe:
+                log.die("can't set {}.{}: permission denied when writing {}{}".
+                        format(section, key, pe.filename,
+                               ('; are you root/administrator?'
+                                if configfile == ConfigFile.SYSTEM else '')))

src/west/configuration.py

@@ -34,6 +34,7 @@ lowest.
 
 import configparser
 import os
+import pathlib
 import platform
 from enum import Enum
 try:
@@ -112,7 +113,7 @@ def update_config(section, key, value, configfile=ConfigFile.LOCAL):
         # Not possible to update ConfigFile.ALL, needs specific conf file here.
         raise ValueError('invalid configfile: {}'.format(configfile))
 
-    filename = _location(configfile)
+    filename = _ensure_config(configfile)
 
     if use_configobj:
         updater = configobj.ConfigObj(filename)
@@ -182,6 +183,29 @@ def _gather_configs(cfg):
     return ret
 
 
+def _ensure_config(configfile):
+    # Ensure the given configfile exists, returning its path. May
+    # raise permissions errors, WestNotFound, etc.
+    #
+    # Uses pathlib as this is hard to implement correctly without it.
+    loc = _location(configfile)
+    path = pathlib.Path(loc)
+
+    if path.is_file():
+        return loc
+
+    # Create the directory. We can't use
+    #     path.parent.mkdir(..., exist_ok=True)
+    # in Python 3.4, so roughly emulate its behavior.
+    try:
+        path.parent.mkdir(parents=True)
+    except FileExistsError:
+        pass
+
+    path.touch(exist_ok=True)
+    return canon_path(str(path))
+
+
 def use_colors():
     # Convenience function for reading the color.ui setting
     return config.getboolean('color', 'ui', fallback=True)

tests/test_config.py

@@ -5,6 +5,7 @@
 import configparser
 import os
 import subprocess
+from unittest.mock import patch
 
 import pytest
 
@@ -24,6 +25,22 @@ def cfg(f=ALL):
     config.read_config(config_file=f, config=cp)
     return cp
 
+def tstloc(cfg):
+    # Monkeypatch for the config file location. assumes we are called
+    # in a tmpdir.
+    #
+    # Important: This is only safe to use to test the API in this process.
+    #            DON'T call cmd('config ...'); subprocesses aren't patched,
+    #            so the system location is the "real" one.
+    if cfg == SYSTEM:
+        return os.path.join(os.getcwd(), 'system', 'config')
+    elif cfg == GLOBAL:
+        return os.path.join(os.getcwd(), 'global', 'config')
+    elif cfg == LOCAL:
+        return os.path.join(os.getcwd(), 'local', 'config')
+    else:
+        raise ValueError('cfg: {}'.format(cfg))
+
 @pytest.fixture(autouse=True)
 def config_tmpdir(tmpdir):
     # Fixture for running from a temporary directory with a .west
@@ -128,6 +145,64 @@ def test_config_local():
     assert 'pytest' not in glb
     assert lcl['pytest']['local2'] == 'foo2'
 
+@patch('west.configuration._location', new=tstloc)
+def test_system_creation():
+    # Test that the system file -- and just that file -- is created on
+    # demand.
+    #
+    # Since we use tstloc(), we can't call cmd('config ...') here.
+    assert not os.path.isfile(tstloc(SYSTEM))
+    assert not os.path.isfile(tstloc(GLOBAL))
+    assert not os.path.isfile(tstloc(LOCAL))
+
+    config.update_config('pytest', 'key', 'val', configfile=SYSTEM)
+
+    assert os.path.isfile(tstloc(SYSTEM))
+    assert not os.path.isfile(tstloc(GLOBAL))
+    assert not os.path.isfile(tstloc(LOCAL))
+    assert cfg(f=ALL)['pytest']['key'] == 'val'
+    assert cfg(f=SYSTEM)['pytest']['key'] == 'val'
+    assert 'pytest' not in cfg(f=GLOBAL)
+    assert 'pytest' not in cfg(f=LOCAL)
+
+@patch('west.configuration._location', new=tstloc)
+def test_global_creation():
+    # Like test_system_creation, for global config options.
+    #
+    # Since we use tstloc(), we can't call cmd('config ...') here.
+    assert not os.path.isfile(tstloc(SYSTEM))
+    assert not os.path.isfile(tstloc(GLOBAL))
+    assert not os.path.isfile(tstloc(LOCAL))
+
+    config.update_config('pytest', 'key', 'val', configfile=GLOBAL)
+
+    assert not os.path.isfile(tstloc(SYSTEM))
+    assert os.path.isfile(tstloc(GLOBAL))
+    assert not os.path.isfile(tstloc(LOCAL))
+    assert cfg(f=ALL)['pytest']['key'] == 'val'
+    assert 'pytest' not in cfg(f=SYSTEM)
+    assert cfg(f=GLOBAL)['pytest']['key'] == 'val'
+    assert 'pytest' not in cfg(f=LOCAL)
+
+@patch('west.configuration._location', new=tstloc)
+def test_local_creation():
+    # Like test_system_creation, for local config options.
+    #
+    # Since we use tstloc(), we can't call cmd('config ...') here.
+    assert not os.path.isfile(tstloc(SYSTEM))
+    assert not os.path.isfile(tstloc(GLOBAL))
+    assert not os.path.isfile(tstloc(LOCAL))
+
+    config.update_config('pytest', 'key', 'val', configfile=LOCAL)
+
+    assert not os.path.isfile(tstloc(SYSTEM))
+    assert not os.path.isfile(tstloc(GLOBAL))
+    assert os.path.isfile(tstloc(LOCAL))
+    assert cfg(f=ALL)['pytest']['key'] == 'val'
+    assert 'pytest' not in cfg(f=SYSTEM)
+    assert 'pytest' not in cfg(f=GLOBAL)
+    assert cfg(f=LOCAL)['pytest']['key'] == 'val'
+
 def test_default_config():
     # Writing to a value without a config destination should default
     # to --local.