Evaluating an annotation always produces the same result

compiler/src/dotty/tools/dotc/core/Annotations.scala

@@ -51,27 +51,36 @@ object Annotations {
     def tree(implicit ctx: Context): Tree = t
   }
 
+  /** The context to use to evaluate an annotation */
+  private def annotCtx(using ctx: Context): Context =
+    // We should always produce the same annotation tree, no matter when the
+    // annotation is evaluated. Setting the phase to a pre-transformation phase
+    // seems to be enough to ensure this (note that after erasure, `ctx.typer`
+    // will be the Erasure typer, but that doesn't seem to affect the annotation
+    // trees we create, so we leave it as is)
+    ctx.withPhaseNoLater(ctx.picklerPhase)
+
   abstract class LazyAnnotation extends Annotation {
     protected var mySym: Symbol | (Context => Symbol)
-    override def symbol(using ctx: Context): Symbol =
+    override def symbol(using parentCtx: Context): Symbol =
       assert(mySym != null)
       mySym match {
         case symFn: (Context => Symbol) @unchecked =>
           mySym = null
-          mySym = symFn(ctx)
-        case sym: Symbol if sym.defRunId != ctx.runId =>
+          mySym = symFn(annotCtx)
+        case sym: Symbol if sym.defRunId != parentCtx.runId =>
           mySym = sym.denot.current.symbol
         case _ =>
       }
       mySym.asInstanceOf[Symbol]
 
     protected var myTree: Tree | (Context => Tree)
-    def tree(using ctx: Context): Tree =
+    def tree(using Context): Tree =
       assert(myTree != null)
       myTree match {
         case treeFn: (Context => Tree) @unchecked =>
           myTree = null
-          myTree = treeFn(ctx)
+          myTree = treeFn(annotCtx)
         case _ =>
       }
       myTree.asInstanceOf[Tree]
@@ -99,12 +108,12 @@ object Annotations {
   abstract class LazyBodyAnnotation extends BodyAnnotation {
     // Copy-pasted from LazyAnnotation to avoid having to turn it into a trait
     protected var myTree: Tree | (Context => Tree)
-    def tree(using ctx: Context): Tree =
+    def tree(using Context): Tree =
       assert(myTree != null)
       myTree match {
         case treeFn: (Context => Tree) @unchecked =>
           myTree = null
-          myTree = treeFn(ctx)
+          myTree = treeFn(annotCtx)
         case _ =>
       }
       myTree.asInstanceOf[Tree]

compiler/test/dotty/tools/AnnotationsTests.scala

@@ -0,0 +1,40 @@
+package dotty.tools
+
+import vulpix.TestConfiguration
+
+import org.junit.Test
+
+import dotc.ast.Trees._
+import dotc.core.Decorators._
+import dotc.core.Contexts._
+import dotc.core.Types._
+
+import java.io.File
+import java.nio.file._
+
+class AnnotationsTest:
+  @Test def annotTreeNotErased: Unit =
+    withJavaCompiled(
+      VirtualJavaSource("Annot.java",
+        "public @interface Annot { String[] values() default {}; }"),
+      VirtualJavaSource("A.java",
+        "@Annot(values = {}) public class A {}")) { javaOutputDir =>
+      withContext(javaOutputDir.toString + File.pathSeparator + TestConfiguration.basicClasspath) {
+        (using ctx: Context) =>
+        val defn = ctx.definitions
+        val cls = ctx.requiredClass("A")
+        val annotCls = ctx.requiredClass("Annot")
+        val arrayOfString = defn.ArrayType.appliedTo(List(defn.StringType))
+
+        ctx.atPhase(ctx.erasurePhase.next) {
+          val annot = cls.getAnnotation(annotCls)
+          // Even though we're forcing the annotation after erasure,
+          // the typed trees should be unerased, so the type of
+          // the annotation argument should be `arrayOfString` and
+          // not a `JavaArrayType`.
+          val arg = annot.get.argument(0).get
+          assert(arg.tpe.isInstanceOf[AppliedType] && arg.tpe =:= arrayOfString,
+            s"Argument $arg had type:\n${arg.tpe}\nbut expected type:\n$arrayOfString")
+        }
+      }
+    }

compiler/test/dotty/tools/DottyTest.scala

@@ -77,7 +77,7 @@ trait DottyTest extends ContextEscapeDetection {
   def checkTypes(source: String, typeStringss: List[List[String]])(assertion: (List[List[Type]], Context) => Unit): Unit = {
     val dummyName = "x_x_x"
     val vals = typeStringss.flatten.zipWithIndex.map{case (s, x)=> s"val ${dummyName}$x: $s = ???"}.mkString("\n")
-    val gatheredSource = s" ${source}\n object A$dummyName {$vals}"
+    val gatheredSource = s"${source}\nobject A$dummyName {$vals}"
     checkCompile("typer", gatheredSource) {
       (tree, context) =>
         implicit val ctx = context

compiler/test/dotty/tools/compilerSupport.scala

@@ -0,0 +1,51 @@
+package dotty.tools
+
+import javax.tools._
+import java.io.File
+import java.nio.file._
+import java.net.URI
+import scala.jdk.CollectionConverters._
+import dotty.tools.dotc._
+import core._
+import core.Contexts._
+import dotc.core.Comments.{ContextDoc, ContextDocstrings}
+
+/** Initialize a compiler context with the given classpath and
+ *  pass it to `op`.
+ */
+def withContext[T](classpath: String)(op: Context ?=> T): T =
+  val compiler = Compiler()
+  val run = compiler.newRun(initCtx(classpath))
+  run.compileUnits(Nil) // Initialize phases
+  op(using run.runContext)
+
+private def initCtx(classpath: String): Context =
+  val ctx0 = (new ContextBase).initialCtx.fresh
+  ctx0.setSetting(ctx0.settings.classpath, classpath)
+  ctx0.setProperty(ContextDoc, new ContextDocstrings)
+  ctx0
+
+/** Compile `javaSources` with javac, then pass the compilation output directory
+ *  to `op`. This directory will be deleted when op returns.
+ */
+def withJavaCompiled[T](javaSources: JavaFileObject*)(op: Path => T): T =
+  val javaOutputDir = Files.createTempDirectory("withJavaCompiled")
+  try
+    val javac = ToolProvider.getSystemJavaCompiler()
+    val options = List("-d", javaOutputDir.toString)
+    javac.getTask(null, null, null, options.asJava, null, javaSources.asJava).call();
+    op(javaOutputDir)
+  finally
+    deleteDirectory(javaOutputDir.toFile)
+
+/** Recursively delete a directory. */
+def deleteDirectory(directory: File): Unit =
+  directory.listFiles.toList.foreach { file =>
+    if (file.isDirectory)
+      deleteDirectory(file)
+    file.delete()
+  }
+
+class VirtualJavaSource(fileName: String, code: String) extends SimpleJavaFileObject(
+    URI.create("string:///" + fileName), JavaFileObject.Kind.SOURCE):
+  override def getCharContent(ignoreEncodingErrors: Boolean): String = code