Fix #1786: support use package object in fun call

Author: liufengyun

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

@@ -418,7 +418,7 @@ trait Checking {
   /** Check that Java statics and packages can only be used in selections.
    */
   def checkValue(tree: Tree, proto: Type)(implicit ctx: Context): tree.type = {
-    if (!proto.isInstanceOf[SelectionProto]) {
+    if (!proto.isInstanceOf[SelectionProto] && !proto.isInstanceOf[ApplyingProto]) {
       val sym = tree.tpe.termSymbol
       // The check is avoided inside Java compilation units because it always fails
       // on the singleton type Module.type.

tests/neg/i1786.scala

@@ -0,0 +1,17 @@
+package scala
+
+package object meta {
+  def apply(x: Int): Int = x * x
+}
+
+class Test {
+  def f(a: Any): Any = f(meta)         // error
+  def g(a: Any): Any = f(scala.meta)   // error
+
+  meta { 5 + 4 }
+
+  scala.meta { 3 }
+
+  val m1 = meta         // error
+  val m2 = scala.meta   // error
+}

tests/pos/i1786.scala

@@ -0,0 +1,18 @@
+package scala
+
+package object meta {
+  def apply(x: Int): Int = x * x
+}
+
+class Test {
+  meta { 5 + 4  }
+
+  scala.meta { 3 }
+
+  scala.meta.`package` { 3 }
+
+  // val m1 = meta         // error
+  // val m2 = scala.meta   // error
+  val m3 = scala.meta.`package`
+  val m4 = meta.`package`
+}