Add linter for any discarded value

[bplommer]

I suggest adding a linter that will warn for any discarded value, regardless of its type. This would both catch unused effectful code that's not concrete IO - it would need to be disabled for blocks of side-effecting code, but I see this as an extra advantage since side-effecting code would have to be explicitly marked as such.

[armanbilge]

Do you think this is something we could upstream to scalafix itself?

I've been staring at your general linters in http4s wondering if they might take them too.

[bplommer]

Good point! The "redundant final object" rule has already been upstreamed and scalafix itself seems to be more actively maintained than it was a while back.

[armanbilge]

I saw that! Nice work on it :) yes, they've been responsive to my ideas to upstream some stuff from our build here too.

[armanbilge]

Linking to:

• Add a linter for discarded values scalacenter/scalafix#1620

[som-snytt]

If someone points me to a repo that demonstrates a gotcha, I will test -Wnonunit-statement against it. Currently, I'm just running it over the compiler project to avoid noise, as opposed to demonstrating utility. I think it noticed one or two possible bugs, but the imperative compiler and library are freely side-effecting.

[Daenyth]

I think this is obsolete now that -Wnonunit-statement exists