💥 Many things

.idea/runConfigurations/Sample.xml

@@ -0,0 +1,25 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Sample" type="PythonConfigurationType" factoryName="Python">
+    <module name="cfig" />
+    <option name="INTERPRETER_OPTIONS" value="" />
+    <option name="PARENT_ENVS" value="true" />
+    <envs>
+      <env name="PYTHONUNBUFFERED" value="1" />
+      <env name="MY_REQUIRED_STRING" value="a" />
+      <env name="MY_REQUIRED_INT" value="not a number" />
+    </envs>
+    <option name="SDK_HOME" value="$PROJECT_DIR$/.venv/bin/python" />
+    <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$/cfig/sample" />
+    <option name="IS_MODULE_SDK" value="true" />
+    <option name="ADD_CONTENT_ROOTS" value="true" />
+    <option name="ADD_SOURCE_ROOTS" value="true" />
+    <option name="SCRIPT_NAME" value="cfig.sample" />
+    <option name="PARAMETERS" value="" />
+    <option name="SHOW_COMMAND_LINE" value="false" />
+    <option name="EMULATE_TERMINAL" value="true" />
+    <option name="MODULE_MODE" value="true" />
+    <option name="REDIRECT_INPUT" value="false" />
+    <option name="INPUT_FILE" value="" />
+    <method v="2" />
+  </configuration>
+</component>

cfig/config.py

@@ -6,6 +6,7 @@ import lazy_object_proxy
 import typing as t
 import logging
 import collections
+import textwrap
 from . import errors
 from . import customtyping as ct
 from cfig.sources.base import Source
@@ -274,6 +275,64 @@ class Configuration:
         log.debug(f"Registering doc {doc!r} in {key!r}")
         self.docs[key] = doc
 
+    def _click_root(self):
+        """
+        Generate the :mod:`click` root of this :class:`.Configuration`.
+        """
+
+        try:
+            import click
+        except ImportError:
+            raise errors.MissingDependencyError(f"To use {self.__class__.__qualname__}.cli, the `cli` optional dependency is needed.")
+
+        @click.command()
+        def root():
+            click.secho(f"=== Configuration ===", fg="bright_white", bold=True)
+            click.secho()
+
+            key_padding = max(map(lambda k: len(k), self.proxies.keys()))
+
+            try:
+                self.proxies.resolve()
+            except errors.BatchResolutionFailure as fail:
+                errors_dict = fail.errors
+            else:
+                errors_dict = {}
+
+            for key, proxy in self.proxies.items():
+                # Weird padding hack
+                # noinspection PyStringFormat
+                key_text = f"{{key:{key_padding}}}".format(key=key)
+
+                if key in errors_dict:
+                    error = errors_dict[key]
+                    if isinstance(error, errors.MissingValueError):
+                        click.secho(f"{key_text} → Required, but not set.", fg="red")
+                    elif isinstance(error, errors.InvalidValueError):
+                        click.secho(f"{key_text} → {' '.join(error.args)}", fg="red")
+                    else:
+                        click.secho(f"{key_text} → {error!r}", fg="white", bg="bright_red")
+                else:
+                    value = self.proxies[key]
+                    click.secho(f"{key_text} = {value.__wrapped__!r}", fg="green")
+
+                doc = self.docs[key]
+                doc = textwrap.dedent(doc)
+                doc = doc.strip("\n")
+                doc = "\n".join(doc.split("\n")[:3])
+
+                click.secho(f"{doc}", fg="white")
+                click.secho()
+
+        return root
+
+    def cli(self):
+        """
+        Run the command-line interface.
+        """
+
+        self._click_root()()
+
 
 __all__ = (
     "Configuration",

cfig/errors.py

@@ -4,11 +4,15 @@ class CfigError(Exception):
     """
 
 
-class DefinitionError(CfigError):
+class DeveloperError(CfigError):
+    """
+    A developer-side error: the user has no way to solve it.
+    """
+
+
+class DefinitionError(DeveloperError):
     """
     An error is present in the definition of a :class:`cfig.Configuration`.
-
-    This is a developer-side error: the user has no way to solve it.
     """
 
 
@@ -32,11 +36,15 @@ class DuplicateProxyNameError(ProxyRegistrationError):
     """
 
 
-class ConfigurationError(CfigError):
+class UserError(CfigError):
+    """
+    A user-side error: the developer of the application has no way to fix it.
+    """
+
+
+class ConfigurationError(UserError):
     """
     An error is present in the configuration specified by the user.
-
-    This is a user-side error: the developer of the application has no way to solve it.
     """
 
 
@@ -46,6 +54,23 @@ class MissingValueError(ConfigurationError):
     """
 
 
+class InvalidValueError(ConfigurationError):
+    """
+    A configuration key has an invalid value.
+
+    This error should be raised by the developer in resolvers if the developer knows that a invalid value has been passed, for example::
+
+        @config.required()
+        def INTEGER(val):
+            try:
+                return int(val)
+            except ValueError:
+                raise InvalidValueError("Not an int.")
+
+    It is not raised automatically, as certain errors might be caused by a mistake in the programming of the resolver.
+    """
+
+
 class BatchResolutionFailure(BaseException):
     """
     A cumulative error which sums the errors occurred while resolving proxied configuration values.
@@ -58,12 +83,23 @@ class BatchResolutionFailure(BaseException):
         return f"<{self.__class__.__qualname__}: {len(self.errors)} errors>"
 
 
+class MissingDependencyError(CfigError):
+    """
+    An optional dependency has not been installed, but it is required by a called function.
+    """
+
+
 __all__ = (
+    "CfigError",
+    "DeveloperError",
     "DefinitionError",
     "UnknownResolverNameError",
     "ProxyRegistrationError",
     "DuplicateProxyNameError",
+    "UserError",
     "ConfigurationError",
     "MissingValueError",
+    "InvalidValueError",
     "BatchResolutionFailure",
+    "MissingDependencyError",
 )

cfig/sample/__main__.py

@@ -0,0 +1,50 @@
+import cfig
+import typing
+
+
+config = cfig.Configuration()
+
+
+@config.required()
+def MY_FAVOURITE_STRING(val: str) -> str:
+    """
+    Your favourite string!
+    """
+    return val
+
+
+@config.optional()
+def MY_OPTIONAL_STRING(val: typing.Optional[str]) -> str:
+    """
+    Your favourite string, including the empty one!
+    """
+    return val or ""
+
+
+@config.required()
+def MY_REQUIRED_INT(val: str) -> int:
+    """
+    Your favourite integer!
+    """
+    try:
+        return int(val)
+    except ValueError:
+        raise cfig.InvalidValueError("Not an int.")
+
+
+@config.required()
+def MY_FAVOURITE_EVEN_INT(val: str) -> int:
+    """
+    Your favourite even number!
+    """
+    try:
+        n = int(val)
+    except ValueError:
+        raise cfig.InvalidValueError("Not an int.")
+    if n % 2:
+        raise cfig.InvalidValueError("Not an even int.")
+    return n
+
+
+if __name__ == "__main__":
+    config.cli()

cfig/tests/test_config.py

@@ -3,6 +3,12 @@ import cfig
 import os
 import lazy_object_proxy
 
+try:
+    import click
+    import click.testing
+except ImportError:
+    click = None
+
 
 class TestConfig:
     def test_creation(self):
@@ -19,7 +25,10 @@ class TestConfig:
         @basic_config.required()
         def FIRST_NUMBER(val: str) -> int:
             """The first number to sum."""
+            try:
                 return int(val)
+            except ValueError:
+                raise cfig.InvalidValueError("Not an int.")
 
         assert isinstance(FIRST_NUMBER, lazy_object_proxy.Proxy)
         assert callable(FIRST_NUMBER.__factory__)
@@ -31,7 +40,10 @@ class TestConfig:
         @basic_config.optional()
         def SECOND_NUMBER(val: str) -> int:
             """The second number to sum."""
+            try:
                 return int(val)
+            except ValueError:
+                raise cfig.InvalidValueError("Not an int.")
 
         assert isinstance(SECOND_NUMBER, lazy_object_proxy.Proxy)
         assert callable(SECOND_NUMBER.__factory__)
@@ -44,12 +56,18 @@ class TestConfig:
         @basic_config.required()
         def FIRST_NUMBER(val: str) -> int:
             """The first number to sum."""
+            try:
                 return int(val)
+            except ValueError:
+                raise cfig.InvalidValueError("Not an int.")
 
         @basic_config.optional()
         def SECOND_NUMBER(val: str) -> int:
             """The second number to sum."""
+            try:
                 return int(val)
+            except ValueError:
+                raise cfig.InvalidValueError("Not an int.")
 
         yield basic_config
 
@@ -74,6 +92,27 @@ class TestConfig:
         with pytest.raises(cfig.MissingValueError):
             numbers_config.proxies.resolve_failfast()
 
+    def test_resolve_invalid(self, numbers_config, monkeypatch):
+        monkeypatch.setenv("FIRST_NUMBER", "a")
+        monkeypatch.setenv("SECOND_NUMBER", "")
+
+        assert os.environ.get("FIRST_NUMBER", "a")
+        assert not os.environ.get("SECOND_NUMBER")
+
+        with pytest.raises(cfig.BatchResolutionFailure) as ei:
+            numbers_config.proxies.resolve()
+            assert isinstance(ei.value.errors["FIRST_NUMBER"], cfig.InvalidValueError)
+
+    def test_resolve_ff_invalid(self, numbers_config, monkeypatch):
+        monkeypatch.setenv("FIRST_NUMBER", "a")
+        monkeypatch.setenv("SECOND_NUMBER", "")
+
+        assert os.environ.get("FIRST_NUMBER", "a")
+        assert not os.environ.get("SECOND_NUMBER")
+
+        with pytest.raises(cfig.InvalidValueError):
+            numbers_config.proxies.resolve_failfast()
+
     def test_resolve_required(self, numbers_config, monkeypatch):
         monkeypatch.setenv("FIRST_NUMBER", "1")
         monkeypatch.setenv("SECOND_NUMBER", "")
@@ -207,3 +246,22 @@ class TestConfig:
 
         assert second_number.__resolved__
         assert second_number == 4
+
+    @pytest.fixture(scope="function")
+    def click_runner(self):
+        yield click.testing.CliRunner()
+
+    @pytest.mark.skipif(click is None, reason="the `cli` extra is not installed")
+    def test_cli(self, numbers_config, monkeypatch, click_runner):
+        monkeypatch.setenv("FIRST_NUMBER", "1")
+        monkeypatch.setenv("SECOND_NUMBER", "")
+
+        assert os.environ.get("FIRST_NUMBER") == "1"
+        assert not os.environ.get("SECOND_NUMBER")
+
+        root = numbers_config._click_root()
+        result = click_runner.invoke(root, [])
+
+        assert result.exit_code == 0
+        assert "FIRST_NUMBER" in result.output
+        assert "SECOND_NUMBER" in result.output

poetry.lock

@@ -388,7 +388,7 @@ cli = ["click"]
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.10"
-content-hash = "1a65fa3bfc354d7c11fc399cf8aebff5e3dc15b5e26983fdecfa92a1e209779a"
+content-hash = "9003e7beceb925ef6b11961ef2a2bb818fbd8f659b312345dd58d86b786e589f"
 
 [metadata.files]
 alabaster = [

pyproject.toml

@@ -9,9 +9,10 @@ license = "MIT"
 python = "^3.10"
 lazy-object-proxy = "^1.7.1"
 click = { version = "^8.1.2", optional = true }
+colorama = { version = "^0.4.4", optional = true }
 
 [tool.poetry.extras]
-cli = ["click"]
+cli = ["click", "colorama"]
 
 [tool.poetry.dev-dependencies]
 pytest = "^7.1.1"