Eta-reduce before pretty-printing if possible

Author: smarter

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -156,6 +156,8 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         if (defn.isTupleClass(cls)) return toTextTuple(args)
         if (isInfixType(tp)) return toTextInfixType(tycon, args)
         return (toTextLocal(tycon) ~ "[" ~ Text(args map argText, ", ") ~ "]").close
+      case EtaExpansion(tycon) =>
+        return toText(tycon)
       case tp: TypeRef =>
         val hideType = !ctx.settings.debugAlias.value && (tp.symbol.isAliasPreferred)
         if (hideType && !ctx.phase.erasedTypes && !tp.symbol.isCompleting) {

tests/repl/i2492.check

@@ -4,5 +4,5 @@ scala> val s: Map {type Map$K =String;type Map$V = Int} = null
 -- [E055] Syntax Error: <console>:5:7 ------------------------------------------
 5 |val s: Map {type Map$K =String;type Map$V = Int} = null
   |       ^^^
-  |       missing type parameter for [K, V] => Map[K, V]
+  |       missing type parameter for Map
 scala> :quit

tests/repl/names.check

@@ -1,5 +1,5 @@
 scala> case class Foo[M[_]](x: M[Int]) 
 defined class Foo
 scala> Foo(Option(1))
-val res0: Foo[[+A] => Option[A]] = Foo(Some(1))
+val res0: Foo[Option] = Foo(Some(1))
 scala> :quit