Scala 3 Support (1000USD Bounty) #2
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@KuceraMartin said he wanted to look into this, but if anyone else wants to try their hand at this feel free to do so |
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Sounds like a fun thing to do |
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I tried doing this and discovered scala/scala3#19480 |
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I discovered scala/scala3#19436 in #3. I also tried a different approach with mirrors and ran into another compiler crash scala/scala3#19493. It seems there are many different ways to approach this. @ghik would you be interested in discussing our thoughts? Maybe together we could find another approach that doesn't break the compiler :D |
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Sure, but I haven't even gotten to porting the macro itself. I just tried to compile tests on Scala 3... |
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Actually I never tried compiling all the tests. Now that I did, I see I'm getting the same compiler crash as you. I started by removing most tests and trying to write a macro that would generate something similar to what the Scala 2 trait TableMacros:
given metadata[V[_[_]]]: Table.Metadata[V] = ???it will at least compile. Later on, you can start adding some tests back. I tried multiple and never ran into that compiler crash. For instance If you're interested in discussing it further, let's connect on Discord (mine is martin.kucera) |
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@KuceraMartin FYI scala/scala3#19480 already has a working fix on the way, I compiled the tests successfully with it I'm going to take a break from this for now, but I'll be happy to discuss details if I come back to it. |
lihaoyi
changed the title
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Hi this sounds like an interesting exercise. I am new to macros but consider this as an opportunity to learn them. So would like to work on it if its ok. If this will be too much of an effort for a macro newbie I am happy for someone else to work on this.Thank you. |
Please go ahead! No need to ask me for permission |
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Hey @vvidlearn, are you still looking into this? I'm curious to look as well but don't want to step on your toes |
Closes #2 ## Macros Just like @KuceraMartin in #3, I ran into scala/scala3#19493 and scala/scala3#19436 when trying to resolve a `TypeMapper` by importing from a `DialectTypeMappers`. As a workaround, I introduced [additional `implicit def`s in the `TableMapper` companion object](https://github.com/com-lihaoyi/scalasql/blob/a7d6c531bf7b9cc2f5e2c175906d2a1e961de206/scalasql/core/src/TypeMapper.scala#L58-L121) that instead rely on an implicit instance of `DialectTypeMappers`, i.e. in a macro: ```scala // bad, causes a compiler crash // TableMacro.scala (dialect: DialectTypeMappers) => { import dialect.* summonInline[TypeMapper[t]] } // good // TypeMapper.scala implicit def stringFromDialectTypeMappers(implicit d: DialectTypeMappers): TypeMapper[String] = d.StringType // TableMacro.scala (dialect: DialectTypeMappers) => { given d: DialectTypeMappers = dialect summonInline[TypeMapper[t]] } ``` ## Supporting changes In addition to building out the macros in Scala 3, the following changes were necessary: 1. Update the generated code to ensure `def`s aren't too far to the left -- this is to silence Scala 3 warnings 2. Convert `CharSequence`s to `String`s explicitly -- see the [error the Scala 3 compiler reported here](9ffeb06) 3. Remove `try` block without a corresponding `catch` -- see the [warning the Scala 3 compiler reported here](011c3f6) 4. Add types to implicit definitions 5. Mark `renderSql` as `private[scalasql]` instead of `protected` -- see the [error the Scala 3 compiler reported here](8e767e3) 6. Use Scala 3.4 -- this is a little unfortunate since it's not the LTS but it's necessary for the Scala 3 macros to [match on higher kinded types like this](https://github.com/com-lihaoyi/scalasql/blob/a7d6c531bf7b9cc2f5e2c175906d2a1e961de206/scalasql/query/src-3/TableMacro.scala#L48-L52). This type of match doesn't work in Scala 3.3 7. Replace `_` wildcards with `?` -- this is to silence Scala 3 warnings 8. Replace `Foo with Bar` in types with `Foo & Bar` -- this is to silence Scala 3 warnings 9. Add the `-Xsource:3` compiler option for Scala 2 -- this is necessary to use the language features mentioned in points 7 and 8 10. Add a number of type annotations to method overrides -- this is to silence warnings reported by the Scala 2 compiler as a result of enabling `-Xsource:3`. All of the warnings relate to the inferred type of the method changing between Scala 2 and 3
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hi @mrdziuban sorry for the late reply, I am just a macro beginner. So it was beyond me. glad you completed it. |
Currently ScalaSql only supports Scala 2.13. Getting it working on Scala 3 would involve porting the table macros, which is one ~100 line file https://github.com/com-lihaoyi/scalasql/blob/main/scalasql/query/src-2/TableMacro.scala. I don't have the knowledge of Scala 3 macros to do it myself, but it shouldn't be hard to port, and the rest of the ScalaSql library should "just work".
To incentivize contribution, I'm putting a 1000USD bounty on resolving this ticket to the first person who can get all the ScalaSql tests passing on Scala 3. This is payable via bank transfer, and at my discretion in case of ambiguity.
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