fix: report malformed GitHub PR responses as GitOperationError

Author: vitali87

pr_split/exceptions.py

@@ -22,6 +22,7 @@ class ErrorMsg(StrEnum):
     PR_CREATE_FAILED = "Failed to create PR for group '{group}': {detail}"
     MERGE_FAILED = "Merge of '{source}' into '{target}' failed: {detail}"
     PR_NOT_FOUND = "PR #{number} not found"
+    PR_RESPONSE_INVALID = "Unexpected response from GitHub for PR #{number}: {detail}"
     PR_NOT_FROM_FORK = (
         "PR #{number} is not from a fork; pass its head branch name instead of the PR number"
     )

pr_split/git_ops/prs.py

@@ -96,9 +96,14 @@ def fetch_fork_pr(pr_number: int) -> ForkPRInfo:
     except GitOperationError as exc:
         raise GitOperationError(ErrorMsg.PR_NOT_FOUND(number=pr_number)) from exc
 
-    pr_data: dict[str, object] = json.loads(raw)
-    head = pr_data["head"]
-    base = pr_data["base"]
+    try:
+        pr_data = json.loads(raw)
+        head = pr_data["head"]
+        base = pr_data["base"]
+    except (json.JSONDecodeError, KeyError, TypeError) as exc:
+        raise GitOperationError(
+            ErrorMsg.PR_RESPONSE_INVALID(number=pr_number, detail=str(exc))
+        ) from exc
 
     if not isinstance(head, dict) or not isinstance(base, dict):
         raise GitOperationError(ErrorMsg.PR_NOT_FOUND(number=pr_number))

tests/test_git_prs_coverage.py

@@ -183,3 +183,16 @@ def test_same_repo_pr_gets_specific_message(self, mock_gh: MagicMock) -> None:
         mock_gh.return_value = json.dumps(pr_data)
         with pytest.raises(GitOperationError, match="PR #42 is not from a fork"):
             fetch_fork_pr(42)
+
+
+class TestFetchForkPrMalformedResponse:
+    @pytest.mark.parametrize(
+        "raw", ["not json", "[]", '{"head": {}}'], ids=["text", "list", "no-base"]
+    )
+    @patch("pr_split.git_ops.prs._run_gh")
+    def test_malformed_response_is_a_git_operation_error(
+        self, mock_gh: MagicMock, raw: str
+    ) -> None:
+        mock_gh.return_value = raw
+        with pytest.raises(GitOperationError, match="Unexpected response from GitHub for PR #42"):
+            fetch_fork_pr(42)