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Do not propagate @tailrec to exported methods #19509

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Jan 23, 2024
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8 changes: 7 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Namer.scala
Original file line number Diff line number Diff line change
Expand Up @@ -1254,7 +1254,13 @@ class Namer { typer: Typer =>
newSymbol(cls, forwarderName, mbrFlags, mbrInfo, coord = span)

forwarder.info = avoidPrivateLeaks(forwarder)
forwarder.addAnnotations(sym.annotations.filterConserve(_.symbol != defn.BodyAnnot))
forwarder.addAnnotations(sym.annotations.filterConserve { annot =>
annot.symbol != defn.BodyAnnot
&& annot.symbol != defn.TailrecAnnot
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@bishabosha bishabosha Jan 22, 2024

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alternatively, could the TailRec check ignore exported methods? - this filtering approach might not be scalable for e.g. macro annotations

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Right, we also need to filter macro annotations.

I think that disabling the behavior where it is checked will be less scalable. For example, I disable the macro annotations on exports I have to find one or more places where this restriction needs to be taken into account. And those places are usually code generation details like exports.

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I also added @main. Might might still need to filter others.

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@nicolasstucki nicolasstucki Jan 23, 2024

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I wonder if we should have a whitelist approach with this one. This would make sure that we never accidentally keep an annotation we do not want.

I tested this on scala3-bootstrapped/testCompilation and it only required the @targetName annotation. Others that should be required are @experimental, @publicInBinary, and showAsInfix.

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The thing is that we will never know what should be the behavior for custom annotations.

The only holistic solution here is to have an @meta-based indication of what to do. This is the approach used to determine whether annotations should go to fields/getters/setters. It would also be appropriate to determine whether it should go to exports/bridges/etc.

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Maybe we need ExportableAnnotation trait that all such annotations should extend to get exported.

&& annot.symbol != defn.MainAnnot
&& !annot.symbol.derivesFrom(defn.MacroAnnotationClass)
&& !annot.symbol.derivesFrom(defn.MainAnnotationClass)
})

if forwarder.isType then
buf += tpd.TypeDef(forwarder.asType).withSpan(span)
Expand Down
5 changes: 5 additions & 0 deletions tests/pos/export-main.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
object Foo:
@main def baz: Int = 1

object Bar:
export Foo.baz // export Foo.baz but not create an new main entry point
10 changes: 10 additions & 0 deletions tests/pos/i19505.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
import scala.annotation.tailrec

object Foo:
@tailrec
def foo(n: Int): Int =
if n == 0 then 0
else foo(n-1)

object Bar:
export Foo.foo // def foo here should not have `@tailrec`
13 changes: 13 additions & 0 deletions tests/run-macros/annot-export/Macro_1.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
import scala.annotation.{experimental, MacroAnnotation}
import scala.quoted._
import scala.collection.mutable.Map

@experimental
class returnClassName extends MacroAnnotation {
def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] =
import quotes.reflect._
tree match
case DefDef(name, params, tpt, _) =>
val rhs = Literal(StringConstant(Symbol.spliceOwner.name.stripSuffix("$")))
List(DefDef.copy(tree)(name, params, tpt, Some(rhs)))
}
10 changes: 10 additions & 0 deletions tests/run-macros/annot-export/Test_2.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
object Bar:
@returnClassName
def f(): String = ??? // def f(): String = "Bar"

object Baz:
export Bar.f // def f(): String = Bar.f(n)

@main def Test =
assert(Bar.f() == "Bar")
assert(Baz.f() == "Bar")
8 changes: 8 additions & 0 deletions tests/warn/i19505.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
import scala.annotation.tailrec

object Foo:
@tailrec
def foo: Int = foo // warn: Infinite recursive call

object Bar:
export Foo.foo // def foo here should not have `@tailrec`
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