Metadata filters raise a cryptic KeyError on unknown/typo'd operators instead of FilterError

[immuhammadfurqan]

Describe the bug

When a metadata filter uses an operator that isn't supported (a typo such as gt/lt/eq/contains instead of >/</==/in, or a wrong logical operator like XOR), document_matches_filter raises a bare KeyError with no guidance, instead of the FilterError that the rest of the filter validation already uses.

This happens in haystack/utils/filters.py, which is the shared filter engine used by InMemoryDocumentStore and every external document store (Weaviate, Pinecone, OpenSearch, …), so the cryptic error surfaces across all stores.

Error message

KeyError: 'gt'

To Reproduce

from haystack.dataclasses import Document
from haystack.utils.filters import document_matches_filter

doc = Document(content="x", meta={"year": 2020})

# comparison operator typo
document_matches_filter({"field": "meta.year", "operator": "gt", "value": 2000}, doc)
# -> KeyError: 'gt'

# logical operator typo
document_matches_filter(
    {"operator": "XOR", "conditions": [{"field": "meta.year", "operator": "==", "value": 2020}]},
    doc,
)
# -> KeyError: 'XOR'

Expected behavior

A FilterError explaining that the operator is unsupported and listing the valid operators — consistent with how other malformed filters (missing keys, wrong value types) are already reported.

System:

• Haystack version: main