fix(config): prevent .pr_agent.toml state leak between repositories

pr_agent/config_loader.py

@@ -1,3 +1,4 @@
+import copy
 from os.path import abspath, dirname, join
 from pathlib import Path
 from typing import Optional
@@ -91,6 +92,37 @@ def _find_pyproject() -> Optional[Path]:
     get_settings().load_file(pyproject_path, env=f'tool.{PR_AGENT_TOML_KEY}')
 
 
+# --- State-leak fix ---------------------------------------------------------
+# Snapshot of global_settings captured on first call to reset_to_startup_defaults().
+# Lazy (not taken at import time) so that startup tasks like
+# apply_secrets_manager_config() that run after module import are included.
+_STARTUP_SETTINGS_SNAPSHOT: Optional[dict] = None
+
+
+def reset_to_startup_defaults():
+    """Restore ``global_settings`` to the state captured at the first call.
+
+    Must be invoked at the top of ``apply_repo_settings()`` so that sections
+    set by a previously-reviewed repo's ``.pr_agent.toml`` do not leak into
+    subsequent PRs processed by the same Python process.
+    """
+    global _STARTUP_SETTINGS_SNAPSHOT
+    if _STARTUP_SETTINGS_SNAPSHOT is None:
+        _STARTUP_SETTINGS_SNAPSHOT = copy.deepcopy(global_settings.as_dict())
+        return  # nothing to restore on the very first call
+
+    current_sections = set(global_settings.as_dict().keys())
+    snapshot_sections = set(_STARTUP_SETTINGS_SNAPSHOT.keys())
+    # Remove sections that appeared after startup (i.e. injected by apply_repo_settings).
+    for section in current_sections - snapshot_sections:
+        global_settings.unset(section)
+    # Restore pre-existing sections to their startup values.
+    for section, contents in _STARTUP_SETTINGS_SNAPSHOT.items():
+        global_settings.unset(section)
+        global_settings.set(section, copy.deepcopy(contents), merge=False)
+# ---------------------------------------------------------------------------
+
+
 def apply_secrets_manager_config():
     """
     Retrieve configuration from AWS Secrets Manager and override existing settings

pr_agent/git_providers/utils.py

@@ -6,13 +6,16 @@
 from dynaconf import Dynaconf
 from starlette_context import context
 
-from pr_agent.config_loader import get_settings
+from pr_agent.config_loader import get_settings, reset_to_startup_defaults
 from pr_agent.git_providers import get_git_provider_with_context
 from pr_agent.log import get_logger
 
 
 def apply_repo_settings(pr_url):
     os.environ["AUTO_CAST_FOR_DYNACONF"] = "false"
+    # Reset first so that .pr_agent.toml from a previously-reviewed repo
+    # cannot leak into this call via the module-level global_settings singleton.
+    reset_to_startup_defaults()
     git_provider = get_git_provider_with_context(pr_url)
     if get_settings().config.use_repo_settings_file:
         repo_settings_file = None

tests/unittest/test_apply_repo_settings.py

@@ -0,0 +1,111 @@
+import copy
+
+import pytest
+
+from pr_agent.config_loader import get_settings, global_settings
+from pr_agent.git_providers import utils as git_utils
+
+
+REPO_A_TOML = b"""
+[pr_reviewer]
+extra_instructions = "MARKER-FROM-REPO-A"
+
+[pr_code_suggestions]
+extra_instructions = "MARKER-FROM-REPO-A"
+"""
+
+
+class FakeGitProvider:
+    """Minimal stand-in used only to feed ``get_repo_settings()`` into
+    ``apply_repo_settings()``."""
+
+    def __init__(self, repo_settings: bytes):
+        self._repo_settings = repo_settings
+
+    def get_repo_settings(self):
+        return self._repo_settings
+
+    # Touched only by handle_configurations_errors() on invalid TOML.
+    def is_supported(self, feature):
+        return False
+
+    def publish_comment(self, body):
+        pass
+
+    def publish_persistent_comment(self, *args, **kwargs):
+        pass
+
+
+@pytest.fixture
+def fresh_global_settings():
+    """Snapshot and restore ``global_settings`` around each test so the
+    module-level Dynaconf singleton doesn't carry state across tests."""
+    snapshot = copy.deepcopy(global_settings.as_dict())
+    yield
+    for section in set(global_settings.as_dict().keys()) - set(snapshot.keys()):
+        global_settings.unset(section)
+    for section, contents in snapshot.items():
+        global_settings.unset(section)
+        global_settings.set(section, copy.deepcopy(contents), merge=False)
+
+
+class TestApplyRepoSettings:
+    def _extra_instructions(self, section: str) -> str:
+        return get_settings().get(f"{section}.extra_instructions", "") or ""
+
+    def test_repo_settings_from_toml_are_applied(
+        self, fresh_global_settings, monkeypatch
+    ):
+        """Sanity: ``apply_repo_settings()`` loads ``extra_instructions`` from a
+        repo's ``.pr_agent.toml``."""
+        monkeypatch.setattr(
+            "pr_agent.git_providers.utils.get_git_provider_with_context",
+            lambda url: FakeGitProvider(REPO_A_TOML),
+        )
+        git_utils.apply_repo_settings(
+            "https://git.example/projects/A/repos/a/pull-requests/1"
+        )
+
+        assert "MARKER-FROM-REPO-A" in self._extra_instructions("pr_reviewer")
+        assert "MARKER-FROM-REPO-A" in self._extra_instructions("pr_code_suggestions")
+
+    def test_repo_without_toml_does_not_inherit_previous_repo_settings(
+        self, fresh_global_settings, monkeypatch
+    ):
+        """Regression: after ``apply_repo_settings()`` loads a repo with a
+        ``.pr_agent.toml``, a subsequent call for a repo WITHOUT
+        ``.pr_agent.toml`` must not still carry the previous repo's
+        ``extra_instructions``.
+
+        Before the fix this failed — the per-section merge in
+        ``apply_repo_settings()`` never cleared state from a prior repo, and
+        when the next repo returned an empty settings blob, the whole load
+        block was skipped and the prior state persisted.
+        """
+        # 1) first repo loads custom instructions
+        monkeypatch.setattr(
+            "pr_agent.git_providers.utils.get_git_provider_with_context",
+            lambda url: FakeGitProvider(REPO_A_TOML),
+        )
+        git_utils.apply_repo_settings(
+            "https://git.example/projects/A/repos/a/pull-requests/1"
+        )
+        assert "MARKER-FROM-REPO-A" in self._extra_instructions("pr_reviewer"), (
+            "precondition: repo A's marker should be present after its load"
+        )
+
+        # 2) second repo has no .pr_agent.toml (get_repo_settings() → b"")
+        monkeypatch.setattr(
+            "pr_agent.git_providers.utils.get_git_provider_with_context",
+            lambda url: FakeGitProvider(b""),
+        )
+        git_utils.apply_repo_settings(
+            "https://git.example/projects/B/repos/b/pull-requests/1"
+        )
+
+        assert "MARKER-FROM-REPO-A" not in self._extra_instructions("pr_reviewer"), (
+            "repo A's [pr_reviewer].extra_instructions leaked into repo B"
+        )
+        assert "MARKER-FROM-REPO-A" not in self._extra_instructions(
+            "pr_code_suggestions"
+        ), "repo A's [pr_code_suggestions].extra_instructions leaked into repo B"