Fix annotation applicability checking

Author: odersky

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

@@ -10,12 +10,14 @@ import util.Spans.Span
 
 object Annotations {
 
+  def annotClass(tree: Tree) given Context =
+    if (tree.symbol.isConstructor) tree.symbol.owner
+    else tree.tpe.typeSymbol
+
   abstract class Annotation {
     def tree(implicit ctx: Context): Tree
 
-    def symbol(implicit ctx: Context): Symbol =
-      if (tree.symbol.isConstructor) tree.symbol.owner
-      else tree.tpe.typeSymbol
+    def symbol(implicit ctx: Context): Symbol = annotClass(tree)
 
     def matches(cls: Symbol)(implicit ctx: Context): Boolean = symbol.derivesFrom(cls)
 

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -1139,8 +1139,9 @@ trait Checking {
   /** check that annotation `annot` is applicable to symbol `sym` */
   def checkAnnotApplicable(annot: Tree, sym: Symbol) given (ctx: Context): Boolean =
     !ctx.reporter.reportsErrorsFor { implicit ctx =>
+      val annotCls = Annotations.annotClass(annot)
       val pos = annot.sourcePos
-      if (annot.symbol == defn.MainAnnot) {
+      if (annotCls == defn.MainAnnot) {
         if (!sym.isRealMethod)
           ctx.error(em"@main annotation cannot be applied to $sym", pos)
         if (!sym.owner.is(Module) || !sym.owner.isStatic)