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Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list #8833

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merged 1 commit into from Jun 2, 2020
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Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list #8833

merged 1 commit into from Jun 2, 2020

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dwijnand
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@dwijnand dwijnand commented Mar 27, 2020 •
edited by SethTisue

Auto-application is dropped in Scala 3:
https://dotty.epfl.ch/docs/reference/dropped-features/auto-apply.html

So it must be deprecated in 2.13 first.

Strongly related to deprecating overriding nullary (and the inverse, overriding nilary): #8846.

Example

$ scala -deprecation -e 'println'
...
warning: Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method println,
or remove the empty argument list from its definition (Java-defined methods are exempt).
In Scala 3, an unapplied method like this will be eta-expanded into a function.
println
^

How to fix

It is recommended to add the missing parens:

$ scala -deprecation -e 'println()'

The change can be made manually or by using scala-rewrites' ExplicitNonNullaryApply.

How to suppress

Since 2.13.2, Scala offers -Wconf:... and @nowarn for warning suppression. You can suppress the new warning globally by passing -Wconf:cat=deprecation&msg=Auto-application:silent to the compiler, or you can suppress it locally by adding @nowarn("cat=deprecation&msg=Auto-application") at the call site.

@scala-jenkins scala-jenkins added this to the 2.13.3 milestone Mar 27, 2020
@dwijnand dwijnand force-pushed the fast-deprecate-auto-application branch from 40187f6 to 073c8ef Compare March 27, 2020 09:41
@lrytz lrytz closed this Mar 27, 2020
@lrytz lrytz reopened this Mar 27, 2020
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lrytz commented Mar 27, 2020

Is there (or could we write) a scalafix rule supporting this change? Scalafix exists for 2.13.1.

@dwijnand dwijnand force-pushed the fast-deprecate-auto-application branch from 073c8ef to 0c40835 Compare March 27, 2020 13:37
@dwijnand dwijnand added the release-notes worth highlighting in next release notes label Mar 31, 2020
@dwijnand dwijnand mentioned this pull request Mar 31, 2020
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Let's leave this one for 2.13.3.

@lrytz lrytz mentioned this pull request Mar 31, 2020
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dwijnand commented Apr 3, 2020

Is there (or could we write) a scalafix rule supporting this change?

lightbend-labs/scala-rewrites#14

@dwijnand dwijnand force-pushed the fast-deprecate-auto-application branch 2 times, most recently from 31fbcf6 to d51c962 Compare April 9, 2020 21:12
@SethTisue SethTisue added the prio:hi high priority (used only by core team, only near release time) label May 12, 2020
@dwijnand dwijnand force-pushed the fast-deprecate-auto-application branch from d51c962 to c78ffa1 Compare May 20, 2020 07:00
@dwijnand dwijnand force-pushed the fast-deprecate-auto-application branch from c78ffa1 to f6c89f7 Compare June 1, 2020 06:55
@dwijnand @SethTisue
Fast-track deprecating auto-application
c900df8 
Auto-application is dropped in Scala 3:
https://dotty.epfl.ch/docs/reference/dropped-features/auto-apply.html

So it must be deprecated in 2.13 first.

Also, AFAICT Object_clone is Java-defined:

    $ qscala
    Welcome to Scala 2.13.2-20200325-150327-bc1cad4 (OpenJDK 64-Bit Server VM, Java 11.0.6).
    Type in expressions for evaluation. Or try :help.

    scala> :power
    Power mode enabled. :phase is at typer.
    import scala.tools.nsc._, intp.global._, definitions._
    Try :help or completions for vals._ and power._

    scala> Object_clone.isJavaDefined
    val res0: Boolean = true
@SethTisue SethTisue force-pushed the fast-deprecate-auto-application branch from f6c89f7 to c900df8 Compare June 1, 2020 22:32
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force-pushed to bump the deprecated-since from 2.13.2 to 2.13.3. let's merge as soon as CI likes it again

@SethTisue SethTisue changed the title Fast-track deprecating auto-application Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list Jun 1, 2020
@SethTisue SethTisue removed the prio:hi high priority (used only by core team, only near release time) label Jun 1, 2020
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@dwijnand dwijnand merged commit f7a498f into scala:2.13.x Jun 2, 2020
@dwijnand dwijnand deleted the fast-deprecate-auto-application branch June 2, 2020 09:07
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