Fix #1503: anonymous application of FunctionX

src/dotty/tools/dotc/typer/Applications.scala

@@ -601,16 +601,16 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
         case _ =>
           tryEither {
             implicit ctx => simpleApply(fun1, proto)
-          } {
-            (failedVal, failedState) =>
-              def fail = { failedState.commit(); failedVal }
-              // Try once with original prototype and once (if different) with tupled one.
-              // The reason we need to try both is that the decision whether to use tupled
-              // or not was already taken but might have to be revised when an implicit
-              // is inserted on the qualifier.
-              tryWithImplicitOnQualifier(fun1, originalProto).getOrElse(
-                if (proto eq originalProto) fail
-                else tryWithImplicitOnQualifier(fun1, proto).getOrElse(fail))
+          } { (failedVal, failedState) =>
+            def fail = { failedState.commit(); failedVal }
+            // Try once with original prototype and once (if different) with tupled one.
+            // The reason we need to try both is that the decision whether to use tupled
+            // or not was already taken but might have to be revised when an implicit
+            // is inserted on the qualifier.
+            tryWithImplicitOnQualifier(fun1, originalProto) getOrElse {
+              if (proto eq originalProto) fail
+              else tryWithImplicitOnQualifier(fun1, proto).getOrElse(fail)
+            }
           }
       }
     }

src/dotty/tools/dotc/typer/Typer.scala

@@ -533,7 +533,16 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def typedBlock(tree: untpd.Block, pt: Type)(implicit ctx: Context) = track("typedBlock") {
     val exprCtx = index(tree.stats)
     val stats1 = typedStats(tree.stats, ctx.owner)
-    val expr1 = typedExpr(tree.expr, pt)(exprCtx)
+
+    // A block might appear in function position after desugaring (see
+    // i1503.scala), so adaptation may insert a `.apply` at the end of expr1.
+    // When this happens we simply remove the select to make expr1 a valid
+    // block expression. The `.apply` will be added back around the block when
+    // the block itself is adapted later.
+    val expr1 = typedExpr(tree.expr, pt)(exprCtx) match {
+      case Select(x, nme.apply) => x
+      case x => x
+    }
     ensureNoLocalRefs(
         assignType(cpy.Block(tree)(stats1, expr1), stats1, expr1), pt, localSyms(stats1))
   }

tests/run/i1503.check

@@ -0,0 +1 @@
+working

tests/run/i1503.scala

@@ -0,0 +1,7 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    (new Function0[Unit] {
+      def apply() = println("working")
+    })()
+  }
+}