Fix #3683: print x.type for singleton types

Author: liufengyun

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

@@ -147,7 +147,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
       case tp: TypeParamRef =>
         ParamRefNameString(tp) ~ lambdaHash(tp.binder)
       case tp: SingletonType =>
-        toTextLocal(tp.underlying) ~ "(" ~ toTextRef(tp) ~ ")"
+        toTextSingleton(tp)
       case AppliedType(tycon, args) =>
         (toTextLocal(tycon) ~ "[" ~ argsText(args) ~ "]").close
       case tp: RefinedType =>
@@ -226,6 +226,9 @@ class PlainPrinter(_ctx: Context) extends Printer {
     }
   }.close
 
+  def toTextSingleton(tp: SingletonType): Text =
+    toTextLocal(tp.underlying) ~ "(" ~ toTextRef(tp) ~ ")"
+
   protected def paramsText(tp: LambdaType): Text = {
     def paramText(name: Name, tp: Type) = toText(name) ~ toTextRHS(tp)
     Text((tp.paramNames, tp.paramInfos).zipped.map(paramText), ", ")

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

@@ -7,7 +7,7 @@ import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.core.NameOps._
 import dotty.tools.dotc.core.Names.Name
 import dotty.tools.dotc.core.Symbols._
-import dotty.tools.dotc.core.Types.ExprType
+import dotty.tools.dotc.core.Types._
 import dotty.tools.dotc.printing.Texts._
 
 
@@ -38,6 +38,11 @@ class ReplPrinter(_ctx: Context) extends DecompilerPrinter(_ctx) {
     }
   }
 
+  override def toTextSingleton(tp: SingletonType): Text = tp match {
+    case ConstantType(const) => toText(const)
+    case _                   => toTextRef(tp) ~ ".type"
+  }
+
   // We don't want the colors coming from RefinedPrinter as the REPL uses its
   // own syntax coloring mechanism.
   override def coloredStr(text: String, color: String): String = text

compiler/test/dotty/tools/repl/ReplCompilerTests.scala

@@ -165,4 +165,9 @@ class ReplCompilerTests extends ReplTest {
       run("IntOrd")
       assertTrue(storedOutput().startsWith("val res0: IntOrd.type ="))
     }
+
+  @Test def testSingletonPrint = fromInitialState { implicit state =>
+    run("""val a = "hello"; val x: a.type = a""")
+    assertEquals("val a: String = hello\nval x: a.type = hello", storedOutput().trim)
+  }
 }