Mix Scala 2 macros in MUnit Scala 3 module #283
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| The next release of MUnit makes use of a new compiler feature that allows you to |
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cc/ @bishabosha @sjrd could you please take a look at this blog post? Please correct me if I got the details wrong
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Live preview at https://olafurpg.github.io/munit/blog/2021/01/05/macromix.html so you can see the rendered SVG files.
With this change, Scala 2.13 users will be able to depend on munit_3.0 artifacts instead of munit_2.13. I wasn't able to manually test this change because MUnit doesn't cross-build for 3.0.0-M1, which is the latest version supported by the `-Ytasty-reader` flag in 2.13.4. Once 2.13.5 is out, it will be easier ot make use of this feature.
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Really cool!
What's the longer plan though? Do we still publish MUnit also for 2.13? If not, I assume Scala 2 users will need to use the full artifact name in sbt to depend on the 3.0 artifact? Either way it may be good to add some notes about this in the user documentation, what do you think?
* Avoid copy-pasted code for Scala 2 macros.
Makes it easier to understand the console output while compiling with Scala 3.
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@gabro thank you for the review!
I was thinking of keeping things unchanged. I updated the post to explain that MUnit 2.13 will continue to be published. The primary purpose of this post is to advocate for this route since I don't everybody are fully aware of the risks of cross-building 2.13 and 3. |
website/blog/2021-01-05-macromix.md
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| upcoming Scala 2.13.5 release will be able to understand newer Scala 3.x | ||
| releases. | ||
| - Some common features in Scala 2 macros don't work in Scala 3. Most notably, | ||
| you can't use quasiquotes or macro bundles. In the case of MUnit, we had to |
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I was confused to find that I could compile a macro bundle using Scala 3.0.0-M1 but the macro expansion failed from Scala 2.13.4 (and not when compiled by Scala 2.13.4), despite the macro bundle having the same bytecode when compiled by either 2.13.4 or 3.0.0-M1, and the tasty to call the macro was the same either way. Something to do with reflective invocation not having the required number of arguments.
It's probably worth opening an issue with the trouble you found, because I don't see at this moment why it should fail.
my example was the following:
class TpeTagImpl(val c: Context) {
import c.universe._
// factory for `final case class TpeTag[T](repr: String)`
// invoked by `implicit def mkTpeTag[T]: TpeTag[T] = macro TpeTagImpl.mkTag[T]`
def mkTag[T](implicit T: c.WeakTypeTag[T]): Tree = {
val tpeString = Literal(Constant(T.tpe.toString))
// new testframework.TpeTag[T](T.tpe.toString)
New(appliedType(c.mirror.staticClass(classOf[testframework.TpeTag[_]].getName()).toType, T.tpe), tpeString)
}
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I removed the macro bundle mention. I didn't try using bundles, I just assumed they wouldn't work because I thought they were implemented with macroparadise.
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I confused bundles with https://github.com/milessabin/macro-compat, which is implemented as a macro annotation to add bundle support in Scala 2.11
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This is very nice work, I will open the issue then for my example.
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@sjrd whoops 😅 I should have waited for your LGTM before merging. |
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No worries. I could have looked at this earlier this morning. ;) |
With this change, Scala 2.13 users will be able to depend on munit_3.0
artifacts instead of munit_2.13.
I wasn't able to manually test this change because MUnit doesn't
cross-build for 3.0.0-M1, which is the latest version supported by the
-Ytasty-readerflag in 2.13.4. Once 2.13.5 is out, it will be easierot make use of this feature.