Add -Vimplicits and -Vtype-diffs

[sideeffffect]

fixes #62

explain types:
https://docs.scala-lang.org/overviews/compiler-options/index.html
https://docs.scala-lang.org/scala3/guides/migration/tooling-migration-mode.html

/cc @mihaisoloi @calvinlfer

[DavidGregory084]

Hi @sideeffffect, I've previously had feedback that folks don't like -Vimplicits or -Vtype-diffs to be enabled by default (see e.g. #38, #45). Has anything changed about the output recently?

[sideeffffect]

Oh, I see.

I don't think these provide much utility in CI. How about we turn these on only in local development mode?

[sideeffffect]

It's a pickle... I like them. But I don't think anything, like the output or whatever has changed since then.

According to #45 (comment) it seems like they cause issues with some tools that drop the color of the font. But that seems more like an issue with Metals and/or Bloop (and should be fixed there), not with sbt-tpolecat or -Vimplicits/-Vtype-diffs...

It would be great to get perspectives from other people and perhaps more in depth explanation why it was disliked. So far we only know that

• it caused long output in Scala 2->3 migration (but that's a once in a lifetime situation and sbt-tpolecat as a whole is not good for that) and that
• one person an everybody they talked to hate it

[mihaisoloi]

@sideeffffect @DavidGregory084 I like them because when working with ZIO 1 especially when it comes to the layers, they really help in distinguishing what is missing in the type. In ZIO 2 that's not that much of an issue to be honest.

[sideeffffect]

Thanks for the feedback @mihaisoloi
Let me stress again that I'm not insistent on having these in sbt-tpolecat. But it would be great to get input from more people, it may turn out that us fans are in the majority.

[DavidGregory084]

@sideeffffect perhaps we should just add these options, but not enable them by default? That would enable those who want to add these options to easily do so.
I'd also be interested to get some feedback from @tpolecat and @DavidGoodenough as to whether they still feel the same about the output of those options. Perhaps we could use their feedback to improve the compiler output?

[sideeffffect]

add these options, but not enable them by default

I'm not sure how much value that has... Anybody can just add their own scalacOptions to deviate from the default.
But let's hear some more feedback 👍

[fdietze]

I always enable those in my code-bases. Whenever I come across an implicit error, where these flags are not enabled, the error is often impossible to fix without them. I agree that they make most sense while developing.

[calvinlfer]

My original use case for these two compiler options was when I was trying to debug shapeless derivation for a bunch of codecs. I agree that it’s not a good idea to keep them on all the time due to the problems they cause but we should allow it to be enabled as options and not as default 🙏

[DavidGregory084]

What do you folks think about adding a VerboseMode which has the new verbose options from this PR in addition to the DevMode options?

Then whoever wants these options enabled by default can set ThisBuild / tpolecatDefaultOptionsMode := VerboseMode, set the env var SBT_TPOLECAT_VERBOSE, or run the tpolecatVerboseMode command to enable them interactively.

[DavidGregory084]

I found that this was added as an alias of -Xlog-implicits for Scala 2.13.0 in #7908.

[DavidGregory084]

Just want to check @sideeffffect whether there was a reason you only wanted to enable this above 2.13.6? Did the behaviour change a lot? I seem to remember -Xlog-implicits used to produce a ton of output.

[DavidGregory084]

The dotty source code says that -explain-types is deprecated in favour of -explain, which solves our explaintypes2/explaintypes3 naming problem.

[DavidGregory084]

What do you folks think about adding a VerboseMode which has the new verbose options from this PR in addition to the DevMode options?

I've made this change on top of @sideeffffect's changes - does this work for everyone? Happy to merge once this goes green if so!

[sideeffffect]

This will make it easier to have verbose errors across different Scala versions. That alone is indeed helpful.
Let's merge this.

[DavidGregory084]

Thanks @sideeffffect! Sorry for the long delay on this one