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Java imports of Scala symbols with trailing $ not inferred #13662

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stuhood opened this issue Nov 18, 2021 · 7 comments · Fixed by #13739
Closed

Java imports of Scala symbols with trailing $ not inferred #13662

stuhood opened this issue Nov 18, 2021 · 7 comments · Fixed by #13739

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@stuhood
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stuhood commented Nov 18, 2021 

akka-http-core/src/main/java/akka/http/javadsl/model/headers/ByteRange.java:7: error: package akka.http.scaladsl.model.headers does not exist
import akka.http.scaladsl.model.headers.ByteRange$;
                                       ^
@stuhood stuhood changed the title Java imports of Scala symbols with $ not inferred Java imports of Scala symbols with trailing $ not inferred Nov 18, 2021
@tdyas
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tdyas commented Nov 20, 2021 •
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This occurs because of the Scala name mangling. The Java reference to akka.http.scaladsl.model.headers.ByteRange is for the Scala object at https://github.com/akka/akka-http/blob/c3f3c9d6cc09e81efc553b45519f91e026939861/akka-http-core/src/main/scala/akka/http/scaladsl/model/headers/ByteRange.scala#L32.

@tdyas
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tdyas commented Nov 20, 2021

Unfortunately, the name mangling is not officially documented and is implementation-specific and so can (and has) changed between scalac versions.

https://github.com/travisbrown/scala-java-interop/blob/master/src/main/java/demo/UsingScala.java provides examples of the name mangling that we could refer to.

Is this worth even doing? If users are importing Scala code into Java files, maybe we should punt and they will have to add explicit dependencies?

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tdyas commented Nov 20, 2021 •
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scala.reflect.NameTransformer exposes some of the name mangling algorithm. Using this could work if we apply it to the "provided names" and expose those names as additional provided names.

@tdyas tdyas mentioned this issue Nov 23, 2021
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tdyas pushed a commit that referenced this issue Nov 23, 2021
[internal] scala: generate the JVM names seen by Java code for Scala …
9e4d9c4 
…code (#13696)

As described in #13662, Java code that tries to import Scala symbols is not having that dependency inferred by Pants. The cause is that the Scala backend does not expose the transformed names seen by Java code for Scala symbols.

For example, the instance for `object Foo` in package `org.pantsbuild.example` is actually `org.pantsbuild.example.Foo$.MODULE$`.

This PR is the first step in solving this by generating the transformed names as part of source analysis. Only the `object` case is handled for now. A subsequent PR will use this information for Java dependency inference.

[ci skip-rust]
@stuhood
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stuhood commented Nov 29, 2021

Fixed by #13696. Thanks @tdyas!

@stuhood stuhood closed this as completed Nov 29, 2021
@tdyas
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tdyas commented Nov 29, 2021

I still have to implement inference in the Python rules using this data.

@tdyas tdyas reopened this Nov 29, 2021
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tdyas commented Nov 29, 2021 •
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The reason is that only the Java rules should consume the mangled names. Scala inference should ignore this data. That seemed like a complicated change so I didn't include that change in #13696.

@tdyas tdyas mentioned this issue Nov 30, 2021
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@stuhood
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stuhood commented Nov 30, 2021

This represented roughly 5% of the issues in akka-http.

@stuhood stuhood mentioned this issue Nov 30, 2021
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stuhood pushed a commit that referenced this issue Nov 30, 2021
[internal] java: infer scala encoded symbols (#13739)
8fc8d0b 
Use analysis of Scala encoded symbols ("name-mangling") to allow inference of those symbols in Java sources. This is the last part of solving #13662.

Fixes #13662.

[ci skip-rust]
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[internal] java: infer scala encoded symbols tdyas/pants
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