`is(symbol == module)` puts a red underline squiggle under `module`, however this is a valid expression.
This is a rather recent addition to the language (including `package`). It is supported by the dmd based engine, but DParser won't keep up with all changes. I can add it to the parser of that engine, though, but not in semantics.
Oh whoops, I didn't realise I wasn't using the DMD engine. I just re-installed on my work PC, and it's not the default.
fixed in https://github.com/dlang/visuald/releases/tag/v0.52.0