Trap all problems with reading repo index file

If it's got malformed contents we still want to be able
to read a butler without using the alias.

python/lsst/daf/butler/_butlerConfig.py

@@ -89,7 +89,7 @@ def __init__(
                 # might not refer explicitly to a directory and we have
                 # check below to guess that.
                 other = str(ButlerRepoIndex.get_repo_uri(other, True))
-            except FileNotFoundError:
+            except Exception:
                 pass
             if other != original_other:
                 resolved_alias = True

python/lsst/daf/butler/_butlerRepoIndex.py

@@ -90,6 +90,10 @@ def _read_repository_index(cls, index_uri: ResourcePathExpression) -> Config:
         except FileNotFoundError as e:
             # More explicit error message.
             raise FileNotFoundError(f"Butler repository index file not found at {uri}.") from e
+        except Exception as e:
+            raise RuntimeError(
+                f"Butler repository index file at {uri} could not be read: {type(e).__qualname__} {e}"
+            ) from e
         cls._cache[uri] = repo_index
 
         return repo_index
@@ -136,7 +140,7 @@ def get_known_repos(cls) -> Set[str]:
         """
         try:
             repo_index = cls._read_repository_index_from_environment()
-        except (FileNotFoundError, KeyError):
+        except Exception:
             return set()
         return set(repo_index)
 
@@ -153,7 +157,7 @@ def get_failure_reason(cls) -> str:
         """
         try:
             cls._read_repository_index_from_environment()
-        except (FileNotFoundError, KeyError) as e:
+        except Exception as e:
             return str(e)
         return ""
 
@@ -189,7 +193,7 @@ def get_repo_uri(cls, label: str, return_label: bool = False) -> ResourcePath:
         """
         try:
             repo_index = cls._read_repository_index_from_environment()
-        except KeyError:
+        except Exception:
             if return_label:
                 return ResourcePath(label, forceAbsolute=False)
             raise

tests/test_butler.py

@@ -620,6 +620,13 @@ def testConstructor(self) -> None:
             with unittest.mock.patch.dict(os.environ, {"DAF_BUTLER_REPOSITORY_INDEX": str(temp_file)}):
                 with self.assertRaisesRegex(FileNotFoundError, "(no known aliases)"):
                     Butler("label")
+        with ResourcePath.temporary_uri(suffix=suffix) as temp_file:
+            # Now with bad contents.
+            with open(temp_file.ospath, "w") as fh:
+                print("'", file=fh)
+            with unittest.mock.patch.dict(os.environ, {"DAF_BUTLER_REPOSITORY_INDEX": str(temp_file)}):
+                with self.assertRaisesRegex(FileNotFoundError, "(no known aliases:.*could not be read)"):
+                    Butler("label")
         with unittest.mock.patch.dict(os.environ, {"DAF_BUTLER_REPOSITORY_INDEX": "file://not_found/x.yaml"}):
             with self.assertRaises(FileNotFoundError):
                 Butler.get_repo_uri("label")