Link preview duplicate url filter considers anchor

[eras]

Description

When sending a URL to a room, a link preview is generated. If the same URL is sent twice, only one preview is generated. However, if the second link is the same but with an #anchor, the link preview is generated twice for the same content (I assume Synapse will not consider the anchor at all for the actual preview generation process).

Steps to reproduce

• Send a URL that produces a link preview twice to a room, but add #anchor to the end of the second URL, e.g. https://github.com/matrix-org/synapse/issues/10088 and https://github.com/matrix-org/synapse/issues/10088#foo
• Witness Synapse generating two link preview for the same content

Expected behaviour: only one link preview is generated.

Version information

• Homeserver: matrix.org

[tulir]

This is a client-side problem (i.e. element web). Synapse doesn't scan messages to generate URL previews, it just fetches previews for whatever URLs the client asks for.

Synapse could optimize caching URL previews by ignoring fragments, but that doesn't really affect what users see.

[eras]

Added issue to Element/Web.