Keep annotation order

compiler/src/dotty/tools/dotc/transform/RepeatableAnnotations.scala

@@ -11,6 +11,8 @@ import Constants._
 import Types._
 import Decorators._
 
+import scala.collection.mutable
+
 class RepeatableAnnotations extends MiniPhase:
 
   override def phaseName: String = RepeatableAnnotations.name
@@ -28,7 +30,7 @@ class RepeatableAnnotations extends MiniPhase:
     tree
 
   private def aggregateAnnotations(annotations: Seq[Annotation])(using Context): List[Annotation] =
-    val annsByType = annotations.groupBy(_.symbol)
+    val annsByType = stableGroupBy(annotations, _.symbol)
     annsByType.flatMap {
       case (_, a :: Nil) => a :: Nil
       case (sym, anns) if sym.derivesFrom(defn.ClassfileAnnotationClass) =>
@@ -50,6 +52,14 @@ class RepeatableAnnotations extends MiniPhase:
       case (_, anns) => anns
     }.toList
 
+  private def stableGroupBy[A, K](ins: Seq[A], f: A => K): scala.collection.MapView[K, List[A]] =
+    val out = new mutable.LinkedHashMap[K, mutable.ListBuffer[A]]()
+    for (in <- ins) {
+      val buffer = out.getOrElseUpdate(f(in), new mutable.ListBuffer)
+      buffer += in
+    }
+    out.view.mapValues(_.toList)
+
 object RepeatableAnnotations:
   val name: String = "repeatableAnnotations"
   val description: String = "aggregate repeatable annotations"

tests/pos/Annotations.scala

@@ -0,0 +1,8 @@
+package foo.bar
+
+import jdk.jfr.Enabled
+
+@Enabled
+@Deprecated
+final class Annotations {
+}

tests/pos/annotations1/a.scala

@@ -0,0 +1,2 @@
+class Annot1(s: String) extends scala.annotation.StaticAnnotation
+class Annot2(s: Class[_]) extends scala.annotation.StaticAnnotation

tests/pos/annotations1/b.scala

@@ -0,0 +1,3 @@
+@Annot1("foo")
+@Annot2(classOf[AnyRef])
+class Test

tests/pos/annotationsJava/Annot1.java

@@ -0,0 +1,5 @@
+import java.lang.annotation.*;
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@Inherited
+@interface Annot1 { String value() default ""; }

tests/pos/annotationsJava/Annot2.java

@@ -0,0 +1,5 @@
+import java.lang.annotation.*;
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@Inherited
+@interface Annot2 { Class value(); }

tests/pos/annotationsJava/b.scala

@@ -0,0 +1 @@
+@Annot1("foo") @Annot2(classOf[AnyRef]) class Test

tests/pos/annotationsJavaRepeatable/Annot1.java

@@ -0,0 +1,13 @@
+import java.lang.annotation.*;
+
+@Repeatable(Annot1.Container.class)
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@interface Annot1 { String value() default "";
+
+    @Retention(RetentionPolicy.RUNTIME)
+    @Target(ElementType.TYPE)
+    public static @interface Container {
+        Annot1[] value();
+    }
+}

tests/pos/annotationsJavaRepeatable/Annot2.java

@@ -0,0 +1,6 @@
+import java.lang.annotation.*;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+@Inherited
+@interface Annot2 { Class value(); }

tests/pos/annotationsJavaRepeatable/b.scala

@@ -0,0 +1 @@
+@Annot1("foo") @Annot2(classOf[String]) @Annot1("bar") class Test