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https://issues.apache.org/jira/browse/SPARK-33285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17245223#comment-17245223
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Yang Jie commented on SPARK-33285:
----------------------------------
{quote}Note that Scala 2.13 has a configurable warning mechanism, making it
possible to hide some warnings: [https://github.com/scala/scala/pull/8373,]
this can be combined with {{-Xfatal-warnings}} to enforce a warning-free build
without actually fixing all warnings.
{quote}
But it seems that we can't suppress all compilation warnings, such as
auto-application, which is different from eta-zero and eta-sam
{code:java}
def checkCanAutoApply(): Boolean = {
if (!isPastTyper && !matchNullaryLoosely) {
context.deprecationWarning(tree.pos, NoSymbol, s"Auto-application to `()`
is deprecated. Supply the empty argument list `()` explicitly to invoke method
${meth.decodedName},\n" +
s"or remove the empty
argument list from its definition (Java-defined methods are exempt).\n"+
s"In Scala 3, an unapplied
method like this will be eta-expanded into a function.", "2.13.3")
}
true
}
{code}
{code:java}
def warnEtaZero(): Boolean = {
if (!settings.warnEtaZero) return true
context.warning(tree.pos,
s"""An unapplied 0-arity method was eta-expanded (due to the expected type
$pt), rather than applied to `()`.
|Write ${Apply(warnTree, Nil)} to invoke method ${meth.decodedName}, or
change the expected type.""".stripMargin,
WarningCategory.LintEtaZero)
true
}
def warnEtaSam(): Boolean = {
if (!settings.warnEtaSam) return true
val sam = samOf(pt)
val samClazz = sam.owner
// TODO: we allow a Java class as a SAM type, whereas Java only allows the
@FunctionalInterface on interfaces -- align?
if (sam.exists && (!samClazz.hasFlag(JAVA) || samClazz.hasFlag(INTERFACE)) &&
!samClazz.hasAnnotation(definitions.FunctionalInterfaceClass))
context.warning(tree.pos,
s"""Eta-expansion performed to meet expected type $pt, which is
SAM-equivalent to ${samToFunctionType(pt)},
|even though $samClazz is not annotated with `@FunctionalInterface`;
|to suppress warning, add the annotation or write out the equivalent
function literal.""".stripMargin,
WarningCategory.LintEtaSam)
true
}
{code}
> Too many "Auto-application to `()` is deprecated." related compilation
> warnings
> --------------------------------------------------------------------------------
>
> Key: SPARK-33285
> URL: https://issues.apache.org/jira/browse/SPARK-33285
> Project: Spark
> Issue Type: Improvement
> Components: Build
> Affects Versions: 3.1.0
> Reporter: Yang Jie
> Priority: Minor
>
> There are too many "Auto-application to `()` is deprecated." related
> compilation warnings when compile with Scala 2.13 like
> {code:java}
> [WARNING] [Warn]
> /spark-src/core/src/test/scala/org/apache/spark/PartitioningSuite.scala:246:
> Auto-application to `()` is deprecated. Supply the empty argument list `()`
> explicitly to invoke method stdev,
> 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.
> {code}
> A lot of them, but it's easy to fix.
> If there is a definition as follows:
> {code:java}
> Class Foo {
> def bar(): Unit = {}
> }
> val foo = new Foo{code}
> Should be
> {code:java}
> foo.bar()
> {code}
> not
> {code:java}
> foo.bar {code}
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