settings.print_toml_config(): Represent sets as sorted lists

In our --json output, we customize pydantic's JSON encoder to represent
sets as sorted lists (thus yielding stable output). Do the same for when
we generate TOML config output (which goes via a JSON encoding step, and
thus is subject to the same issue with how sets are encoded).

This was discovered while attempting to test how multiple 'pyenvs' were
represented in our TOML output.

Author: jherland

fawltydeps/settings.py

@@ -4,12 +4,13 @@
 import logging
 import sys
 from enum import Enum
-from functools import total_ordering
+from functools import partial, total_ordering
 from pathlib import Path
 from typing import ClassVar, List, Optional, Set, TextIO, Tuple, Type, Union
 
 from pydantic import BaseSettings
 from pydantic.env_settings import SettingsSourceCallable  # pylint: disable=E0611
+from pydantic.json import custom_pydantic_encoder  # pylint: disable=no-name-in-module
 
 from fawltydeps.types import CustomMapping, ParserChoice, PathOrSpecial, TomlData
 
@@ -211,7 +212,9 @@ def print_toml_config(settings: Settings, out: TextIO = sys.stdout) -> None:
     """Serialize the given Settings object into a TOML config section."""
     # Use JSON serialization as a basis for TOML output. Load that back into
     # Python and then use Python's repr() representation below
-    simple_settings = json.loads(settings.json())
+    set_sort = partial(sorted, key=str)
+    encoder = partial(custom_pydantic_encoder, {frozenset: set_sort, set: set_sort})
+    simple_settings = json.loads(json.dumps(settings, default=encoder))
     defaults = {
         name: field.default for name, field in settings.__class__.__fields__.items()
     }

tests/test_cmdline.py

@@ -902,6 +902,30 @@ def test_cmdline_on_ignored_undeclared_option(
             ).splitlines(),
             id="generate_toml_config_with_a_setting_set_to_str_None",
         ),
+        pytest.param(
+            {"pyenvs": ["foo", "bar"]},
+            ["--pyenv", "baz", "xyzzy", "--generate-toml-config"],
+            dedent(
+                """\
+                # Copy this TOML section into your pyproject.toml to configure FawltyDeps
+                # (default values are commented)
+                [tool.fawltydeps]
+                # actions = ['check_undeclared', 'check_unused']
+                # output_format = 'human_summary'
+                # code = ['.']
+                # deps = ['.']
+                pyenvs = ['baz', 'xyzzy']
+                # custom_mapping_file = []
+                # ignore_undeclared = []
+                # ignore_unused = []
+                # deps_parser_choice = ...
+                # install_deps = false
+                # verbosity = 0
+                # [tool.fawltydeps.custom_mapping]
+                """
+            ).splitlines(),
+            id="generate_toml_config_with_multiple_pyenvs",
+        ),
     ],
 )
 def test_cmdline_args_in_combination_with_config_file(