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Fix override checking for Java methods with covariant array #24408

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Fix override checking for Java methods with covariant array #24408

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e29c66d
Add test for #24074
tanishiking Nov 11, 2025
5e43e34
Fix override checking for Java methods with covariant array
tanishiking Nov 13, 2025
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9 changes: 7 additions & 2 deletions compiler/src/dotty/tools/dotc/core/Denotations.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -480,9 +480,14 @@ object Denotations {

val matchLoosely = sym1.matchNullaryLoosely || sym2.matchNullaryLoosely

if symScore <= 0 && info2.overrides(info1, matchLoosely, checkClassInfo = false) then
val compareCtx =
if sym1.is(JavaDefined) && sym2.is(JavaDefined) then
ctx.withProperty(TypeComparer.ComparingJavaMethods, Some(()))
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@tanishiking tanishiking Nov 13, 2025 •
edited
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Let TypeComparer know we're comparing Java defined methods, since TypeComparer alone can't tell the symbols are defined in Java.
Not sure this is legid usage of Context#property?

else ctx

if symScore <= 0 && info2.overrides(info1, matchLoosely, checkClassInfo = false)(using compareCtx) then
denot2
else if symScore >= 0 && info1.overrides(info2, matchLoosely, checkClassInfo = false) then
else if symScore >= 0 && info1.overrides(info2, matchLoosely, checkClassInfo = false)(using compareCtx) then
denot1
else
val jointInfo = infoMeet(info1, info2, safeIntersection)
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22 changes: 21 additions & 1 deletion compiler/src/dotty/tools/dotc/core/TypeComparer.scala
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Expand Up @@ -993,7 +993,20 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
(sym1 eq NullClass) && isNullable(tp2)
}
case tp1 @ AppliedType(tycon1, args1) =>
compareAppliedType1(tp1, tycon1, args1)
// Special case: Java arrays are covariant.
// When checking overrides (frozenConstraint) of Java methods, allow B[] <: A[] if B <: A.
def checkJavaArrayCovariance: Boolean = tp2 match {
case AppliedType(tycon2, arg2 :: Nil)
if frozenConstraint
&& tycon1.typeSymbol == defn.ArrayClass
&& tycon2.typeSymbol == defn.ArrayClass
&& args1.length == 1 =>
// Arrays are covariant in Java: B[] <: A[] if B <: A
isSubType(args1.head, arg2)
case _ => false
}
(ctx.property(ComparingJavaMethods).isDefined && checkJavaArrayCovariance)
|| compareAppliedType1(tp1, tycon1, args1)
case tp1: SingletonType =>
def comparePaths = tp2 match
case tp2: (TermRef | ThisType) =>
Expand Down Expand Up @@ -3356,6 +3369,13 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling

object TypeComparer {

import util.Property

/** A property key to indicate we're comparing Java-defined methods.
* When it is set, arrays are treated as covariant for override checking.
*/
val ComparingJavaMethods = new Property.Key[Unit]

/** A richer compare result, returned by `testSubType` and `test`. */
enum CompareResult:
case OK, OKwithGADTUsed, OKwithOpaquesUsed
Expand Down
17 changes: 17 additions & 0 deletions tests/pos/i24074/JavaPart.java
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@@ -0,0 +1,17 @@
public class JavaPart {
public interface A { }
public interface B extends A {
int onlyInB();
}

public interface Lvl1 {
A[] getData();
}

public interface Lvl2 extends Lvl1 {
@Override
B[] getData();
}

public interface Lvl3 extends Lvl2, Lvl1 { }
}
3 changes: 3 additions & 0 deletions tests/pos/i24074/Test.scala
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@@ -0,0 +1,3 @@
object Test:
def test(lvl3: JavaPart.Lvl3): Unit =
lvl3.getData.head.onlyInB()
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