Search highlights are always empty for SQLite

[mlaily]

Description

When doing a full text search query in one or multiple rooms, the highlights property returned in the response is always empty when using the SQLite database.

This is more of a missing implementation than a bug since this behavior looks intentional

synapse/synapse/storage/databases/main/search.py

Line 535 in 52f456a

if isinstance(self.database_engine, PostgresEngine):

I'm filing it as a bug anyway because this unfortunately breaks the search feature on the Element Android app at least. element-hq/element-android#8729

Steps to reproduce

Run any full text search on a homeserver using SQLite

Homeserver

any homeserver using SQLite

Synapse Version

all versions (still present in the latest 1.102)

Installation Method

Docker (matrixdotorg/synapse)

Database

SQLite

Workers

Single process

Platform

Any

Configuration

No response

Relevant log output

N/A

Anything else that would be useful to know?

No response