Fix crash loading a ruleset that has no config

[Adarsh04Arun]

Sources.from_path() calls add_config() unconditionally, so a ruleset with no config.yaml and no config/*.yaml passes zero sources to SourcesConfig and trips assert sources, 'sources can not be empty'.

A config is not required: Sources.__init__ already substitutes an empty one. Make add_config() a no-op when given no sources so that default applies, and replace the assert with a ValueError (asserts are stripped under -O).

Description

Two crashes on a ruleset that has no config.yaml and no config/*.yaml.

1. Loading fails. Sources.from_path() calls add_config() unconditionally, so
zero sources reach SourcesConfig and trip a bare assert:

$ mkdir -p ruleset && echo 'Foo = 1' > ruleset/main.sml
$ python -c "from pathlib import Path; from osprey.engine.ast.sources import Sources; Sources.from_path(Path('ruleset'))"
AssertionError: sources can not be empty

A config is not required — Sources.__init__ already substitutes an empty
SourcesConfig when none is supplied; from_path just defeated that fallback.
add_config() is now a no-op when given no sources, so the existing default applies.
The assert also becomes a ValueError, since asserts are stripped under -O.

2. Serialising fails. SourcesConfig.__init__ returns early when contents are
empty without setting _source, so the source property raises:

AttributeError: 'SourcesConfig' object has no attribute '_source'

That breaks Sources.to_dict(), which EtcdSourcesPublisher.publish_sources() calls
to push rules to etcd. _source is now set on that path too.

The second crash was previously masked by the first: from_path blew up before
anything could reach to_dict(). Fixing only the first would move the failure from
load time to publish time, so both belong together.

Tests

Adds osprey_worker/src/osprey/engine/ast/tests/test_sources.py (10 tests) covering
config-less loading, root config.yaml, config/*.yaml, to_dict() round-tripping,

Checklist

• Tests pass locally
• uv run ruff check . passes (no unused imports or other lint errors)
• uv tool run fawltydeps --check-unused --pyenv .venv passes (no unused dependencies)
• Updated CHANGELOG.md with my changes, if notable (refer to Keep a Changelog conventions)

Summary by CodeRabbit

• Bug Fixes

  • Rulesets without a configuration source are now accepted.
  • Configuration validation now reports a clear error when no sources are provided.
  • Duplicate configuration sources continue to be rejected with an explicit error.

• Tests

  • Added coverage for source discovery, optional configuration loading, empty configurations, and duplicate configuration handling.

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• osprey_worker/src/osprey/engine/ast/sources.py
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• osprey_worker/src/osprey/engine/ast/sources.py

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📝 Walkthrough

Walkthrough

The change makes empty configuration input a no-op, adds explicit validation for zero sources, initializes empty configuration sources, and tests discovery, loading, serialization, and round-tripping.

Changes

Configuration sources

Layer / File(s)	Summary
Optional configuration source handling osprey_worker/src/osprey/engine/ast/sources.py, osprey_worker/src/osprey/engine/ast/tests/test_sources.py	SourcesBuilder.add_config returns unchanged when no sources are provided. Tests cover source discovery, root and directory configuration loading, optional configuration, and duplicate configuration rejection.
Empty configuration validation osprey_worker/src/osprey/engine/ast/sources.py, osprey_worker/src/osprey/engine/ast/tests/test_sources.py	SourcesConfig raises ValueError when constructed without sources. Empty configuration content now creates an empty Source, and tests cover serialization, round-tripping, and source access.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to c3ea3

Rulesets without configuration files now load and serialize safely while retaining validation for invalid configuration input. No current merge-blocking risk is identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 7.14% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: fixing a crash when loading a ruleset without a configuration file.

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Actionable comments posted: 1

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Inline comments:
In `@osprey_worker/src/osprey/engine/ast/sources.py`:
- Around line 142-143: Update the empty-source handling in Sources.from_path and
SourcesConfig so the empty configuration path initializes _source before
returning, ensuring Sources.build produces a fully initialized config. Add a
regression test asserting Sources.from_path(...).to_dict() succeeds for no
configuration files.

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• osprey_worker/src/osprey/engine/ast/sources.py
• osprey_worker/src/osprey/engine/ast/tests/test_sources.py

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