Generalize test to function classes

The previous test was too struct, missed cases where
some arguments of the function were unbound. i583a.scala
contains a test case.

3 files changed, 21 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index b689c8750..d54c9f731 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1054,8 +1054,8 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def typedAsFunction(tree: untpd.Tree, pt: Type)(implicit ctx: Context): Tree = {
     val pt1 = if (defn.isFunctionType(pt)) pt else AnyFunctionProto
     var res = typed(tree, pt1)
-    if (pt1.eq(AnyFunctionProto) && !defn.isFunctionType(res.tpe)) {
-      def msg = "not a function; cannot be followed by `_'"
+    if (pt1.eq(AnyFunctionProto) && !defn.isFunctionClass(res.tpe.classSymbol)) {
+      def msg = i"not a function: ${res.tpe}; cannot be followed by `_'"
       if (ctx.scala2Mode) {
         ctx.migrationWarning(msg, tree.pos)
         res = typed(untpd.Function(Nil, untpd.TypedSplice(res)))
diff --git a/tests/neg/i941.scala b/tests/neg/i941.scala
new file mode 100644
index 000000000..2643c2546
--- /dev/null
+++ b/tests/neg/i941.scala
@@ -0,0 +1,9 @@
+object Test {
+
+  def bar(tl: => String) = {
+    val x = tl _ //error
+    val y = x _ // error
+    val s: String = x() // error
+  }
+
+}
diff --git a/tests/pos/i941.scala b/tests/pos/i941.scala
new file mode 100644
index 000000000..75bf4e448
--- /dev/null
+++ b/tests/pos/i941.scala
@@ -0,0 +1,10 @@
+object Test {
+
+  class C[A] {
+
+    def this(y: A) = { this(); foo(y) }
+
+    def foo(x: A): Unit = ()
+
+  }
+}