Add empty case class params check. Add test.

[ashwinbhaskar]

Fixes #6969

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[ashwinbhaskar]

@allanrenucci can this be merged ?

[allanrenucci]

We already have some broken logic in Desugar.scala: https://github.com/lampepfl/dotty/blob/073c7aa47672c02932904dcd50bf5693d90d7299/compiler/src/dotty/tools/dotc/ast/Desugar.scala#L449-L451

We should unify both. Let's fix the code in Desugar. Then we probably don't need to report an error in the Parser

[ashwinbhaskar]

We already have some broken logic in Desugar.scala:

https://github.com/lampepfl/dotty/blob/073c7aa47672c02932904dcd50bf5693d90d7299/compiler/src/dotty/tools/dotc/ast/Desugar.scala#L449-L451

We should unify both. Let's fix the code in Desugar. Then we probably don't need to report an error in the Parser

@allanrenucci Not exactly sure where Desugar comes into picture. I am guessing it comes before Parser? If so isn't this code

if (isCaseClass && originalTparams.isEmpty) 
   ctx.error(CaseClassMissingParamList(cdef), namePos) 

taking care of reporting the MissingParam error?

[ashwinbhaskar]

@allanrenucci On a side note, is there a way to run only a particular test?

sbt "test:testOnly *EmptyCaseClassParams"

does not seem to work.

[allanrenucci]

is there a way to run only a particular test?

Yes. Within sbt:

sbt:dotty> testCompilation EmptyCaseClassParams

Alternatively, you can compile a specific file using:

sbt:dotty> dotc path/to/file.scala

Not exactly sure where Desugar comes into picture. I am guessing it comes before Parser?

No it comes right after Parser

If so isn't this code ... taking care of reporting the MissingParam error?

Yes, but it currently does not report an error when the type parameter list in non empty. Removing originalTparams.isEmpty should fix the issue. Not sure if it will handle enums as well.

[ashwinbhaskar]

@allanrenucci done the changes. The Desugar file fix suffices, even for enums

[allanrenucci]

Otherwise LGTM. Thanks a lot @ashwinbhaskar!

[ashwinbhaskar]

Otherwise LGTM. Thanks a lot @ashwinbhaskar!

more than happy to do it 😄

[nicolasstucki]

Thanks @ashwinbhaskar. Nice fix.

[nicolasstucki]

Just a small last detail. Could you change the commit message to Fix #6969: Add empty case class params check so that github will link the commit with the issue.

[ashwinbhaskar]

Just a small last detail. Could you change the commit message to Fix #6969: Add empty case class params check so that github will link the commit with the issue.

Sure, done.