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allow annotations to annotate themselves #24447

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allow annotations to annotate themselves #24447

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35 changes: 20 additions & 15 deletions compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -668,6 +668,7 @@ class TreeUnpickler(reader: TastyReader,
else
newSymbol(ctx.owner, name, flags, completer, privateWithin, coord)
}
registerSym(start, sym)
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@hamzaremmal hamzaremmal Nov 16, 2025 •
edited
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We need to register the symbol before we resolve the annotations (2 lines below)

val annotOwner =
if sym.owner.isClass then newLocalDummy(sym.owner) else sym.owner
sym.annotations = annotFns.map(_(annotOwner))
Expand All @@ -685,7 +686,6 @@ class TreeUnpickler(reader: TastyReader,
cls.enter(sym)
case _ =>
}
registerSym(start, sym)
if (isClass) {
if sym.owner.is(Package) && withCaptureChecks then
sym.setFlag(CaptureChecked)
Expand Down Expand Up @@ -768,7 +768,10 @@ class TreeUnpickler(reader: TastyReader,
addFlag(Protected)
privateWithin = readWithin
case ANNOTATION =>
annotFns = readAnnot :: annotFns
val annotFn =
val annot = readAnnot
(sym: Symbol) => annot.complete(sym)
annotFns = annotFn :: annotFns
case tag =>
assert(false, s"illegal modifier tag $tag at $currentAddr, end = $end")
}
Expand All @@ -778,21 +781,23 @@ class TreeUnpickler(reader: TastyReader,

private def readWithin(using Context): Symbol = readType().typeSymbol

private def readAnnot(using Context): Symbol => Annotation =
private def readAnnot(using Context): Trees.Lazy[Symbol => Annotation] =
readByte()
val end = readEnd()
val tp = readType()
val lazyAnnotTree = readLaterWithOwner(end, _.readTree())
owner =>
new DeferredSymAndTree(tp.typeSymbol, lazyAnnotTree(owner).complete):
// Only force computation of symbol if it has the right name. This added
// amount of laziness is sometimes necessary to avid cycles. Test case pos/i15980.
override def hasSymbol(sym: Symbol)(using Context) = tp match
case tp: TypeRef =>
tp.designator match
case name: Name => name == sym.name && tp.symbol == sym
case _ => tp.symbol == sym
case _ => this.symbol == sym
readLater(end, reader =>
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@hamzaremmal hamzaremmal Nov 16, 2025

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We delay it because reading the type of the annotation tp will fail; we prepare this call before registering the symbol and we cannot do it after.

val tp = reader.readType()
val lazyAnnotTree = reader.readLaterWithOwner(end, _.readTree())
owner =>
new DeferredSymAndTree(tp.typeSymbol, lazyAnnotTree(owner).complete):
// Only force computation of symbol if it has the right name. This added
// amount of laziness is sometimes necessary to avoid cycles. Test case pos/i15980.
override def hasSymbol(sym: Symbol)(using Context) = tp match
case tp: TypeRef =>
tp.designator match
case name: Name => name == sym.name && tp.symbol == sym
case _ => tp.symbol == sym
case _ => this.symbol == sym
)

/** Create symbols for the definitions in the statement sequence between
* current address and `end`.
Expand Down
16 changes: 6 additions & 10 deletions compiler/src/dotty/tools/dotc/typer/Namer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -896,16 +896,12 @@ class Namer { typer: Typer =>
original.mods.withAnnotations:
original.mods.annotations.mapConserve: annotTree =>
val cls = typedAheadAnnotationClass(annotTree)(using annotCtx)
if (cls eq sym)
report.error(em"An annotation class cannot be annotated with iself", annotTree.srcPos)
annotTree
else
val ann =
if cls.is(JavaDefined) then Checking.checkNamedArgumentForJavaAnnotation(annotTree, cls.asClass)
else annotTree
val ann1 = Annotation.deferred(cls)(typedAheadExpr(ann)(using annotCtx))
sym.addAnnotation(ann1)
ann
val ann =
if cls.is(JavaDefined) then Checking.checkNamedArgumentForJavaAnnotation(annotTree, cls.asClass)
else annotTree
val ann1 = Annotation.deferred(cls)(typedAheadExpr(ann)(using annotCtx))
sym.addAnnotation(ann1)
ann
case _ =>
}

Expand Down
1 change: 0 additions & 1 deletion tests/neg/i1212.scala
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1 change: 1 addition & 0 deletions tests/pos/i1212.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
@ann class ann extends scala.annotation.Annotation
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