init subcommand: post-installation system initialization (#16)

## Summary

Adds subcommand `init` with its own subcommands:

* `conf`: write default/example conf files to default directory or to a specified directory

* `comp`: write shell completion files for user or system or to a specified directory

Part of #15 

## Changes

* system path prefixes: ignore isolation in system context + refactoring for flexibility

* added subcommand `init` for post-installation initialization beginning with: shell completion files

* init comp: ensure directory exists before writing file

* added subcommand `init conf` to write default/example conf files to default directory or specified directory.

  * includes (related) upgrade to argcmdr 1.0.0
  * display `python -m fate` rather than `fate` when run that way

pyproject.toml

@@ -12,7 +12,8 @@ packages = [{include = "fate", from = "src"}]
 
 [tool.poetry.dependencies]
 python = "^3.8"
-argcmdr = "^0.13.2"
+argcmdr = "^1.0.0"
+argcomplete = "^2.0"
 croniter = "^1.3.5"
 Jinja2 = "^3.1.2"
 loguru = "^0.6.0"

src/fate/cli/__init__.py

@@ -1,3 +1,3 @@
-from .base import runcmd  # noqa: F401
+from .base import exit_on_error, runcmd  # noqa: F401
 
 from .root import main, Main, daemon, serve  # noqa: F401

src/fate/cli/base/__init__.py

@@ -1,2 +1,3 @@
-from .execution import runcmd  # noqa: F401
-from .main import Main         # noqa: F401
+from .common import exit_on_error  # noqa: F401
+from .execution import runcmd      # noqa: F401
+from .main import Main             # noqa: F401

src/fate/cli/base/common.py

@@ -1,4 +1,5 @@
 import enum
+import functools
 
 import fate.conf
 
@@ -32,6 +33,24 @@ def __exit__(self, exc_type, exc_value, _traceback):
             self.parser.exit(78, f'{self.parser.prog}: error: {exc_value}\n')
 
 
+def exit_on_error(method):
+    """Decorator to apply context manager `ExitOnError` to instance
+    methods of classes of type `argcmdr.Command`.
+
+    Note: The decorator wrapper depends upon instance attribute
+    `parser`. As such, affected command classes must extend the default
+    `__init__` (*i.e.* `super()`); or, decorated methods must be invoked
+    *after* command initialization (*i.e.* not as part of its `__init__`).
+
+    """
+    @functools.wraps(method)
+    def wrapped(self, *args, **kwargs):
+        with ExitOnError(self.parser):
+            return method(self, *args, **kwargs)
+
+    return wrapped
+
+
 class CommandInterface:
 
     class CommandStatus(enum.Enum):
@@ -59,7 +78,7 @@ def __str__(self):
 
     @property
     def conf(self):
-        if not self.__parents__:
+        if (root := self.root) is None:
             # this is the root command
             # retrieve and store conf here
             try:
@@ -70,11 +89,11 @@ def conf(self):
             return conf
 
         # defer to root
-        return self.root.conf
+        return root.conf
 
     @property
     def exit_on_error(self):
-        return ExitOnError(self.args.__parser__)
+        return ExitOnError(self.parser)
 
     @staticmethod
     def write_result(path, contents):

src/fate/cli/base/execution.py

@@ -133,7 +133,7 @@ def get_command(self, args):
     def prepare(self, args, parser):
         """Execute and report on task command execution."""
         try:
-            command_spec = self.call(args, 'get_command')
+            command_spec = self.delegate('get_command')
         except self.local.CommandNotFound as exc:
             hint = ('\nhint: whitespace in program name suggests a misconfiguration'
                     if re.search(r'\s', exc.program) else '')

src/fate/cli/base/main.py

@@ -1,3 +1,6 @@
+import os.path
+import sys
+
 import argcmdr
 
 from .common import CommandInterface
@@ -7,11 +10,12 @@ class Main(CommandInterface, argcmdr.RootCommand):
     """manage the periodic execution of commands"""
 
     @classmethod
-    def base_parser(cls):
-        parser = super().base_parser()
+    def _new_parser_(cls):
+        parser = super()._new_parser_()
 
         # enforce program name when invoked via "python -m fate"
         if parser.prog == '__main__.py':
-            parser.prog = 'fate'
+            command = os.path.basename(sys.executable)
+            parser.prog = f'{command} -m fate'
 
         return parser

src/fate/cli/command/control.py

@@ -148,9 +148,7 @@ def onerror(self, exc):
         error_msg = error and f': {error}'
         error_name = exc.__class__.__name__
 
-        parser = self.args.__parser__
-
-        parser.exit(1, f'{parser.prog}: fatal: {error_name}{error_msg}\n')
+        self.parser.exit(1, f'{self.parser.prog}: fatal: {error_name}{error_msg}\n')
 
     def __call__(self, args, parser):
         """Execute the command."""