Don't specialize abstract apply

Author: liufengyun

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

@@ -41,7 +41,7 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
 
           val apply = baseType.member(nme.apply)
           val overrideApply = tp.decls.find {  sym =>
-            sym.is(Flags.Method) && sym.name == nme.apply && sym.info.matches(apply.info)
+            sym.is(Flags.Method, butNot = Flags.Deferred) && sym.name == nme.apply && sym.info.matches(apply.info)
           }
 
           def isSpecializable = defn.isSpecializableFunction(sym.asClass, argTypes, retType)

compiler/test/dotty/tools/dotc/transform/SpecializeFunctionsTests.scala

@@ -67,6 +67,28 @@ class SpecializeFunctionsTests extends DottyBytecodeTest {
     }
   }
 
+  @Test def notSpecializeAbstractMethod = {
+    val source =
+      """|trait Vector extends (Int=>Int) {
+         |  override def apply(i: Int): Int
+         |}""".stripMargin
+
+    checkBCode(source) { dir =>
+      val apps =
+        findClass("Vector", dir).methods.asScala.collect {
+          case m if m.name == "apply$mcII$sp" => m
+          case m if m.name == "apply" => m
+        }
+        .map(_.name)
+        .toList
+
+      assert(
+        apps.length == 1,
+        s"Wrong number of specialized applys, actual length: ${apps.length} - $apps"
+      )
+    }
+  }
+
   @Test def noBoxingSpecFunction0 = {
     implicit val source: String =
       """|class Test {