revert the change to typer

Author: liufengyun

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

@@ -77,11 +77,17 @@ object RefChecks {
 
   /** Check that a stable identifier pattern is indeed stable (SLS 8.1.5)
    */
-  private def checkStableIdentPattern(tree: Tree)(implicit ctx: Context) = tree match {
-    case _: Select | _: Ident if !isWildcardArg(tree)  =>
-      if (!tree.tpe.isStable)
-        ctx.error(s"stable identifier required, but ${tree.show} found", tree.pos)
-    case _ =>
+  private def checkStableIdentPattern(tree: Tree)(implicit ctx: Context) = {
+    def error = ctx.error(s"stable identifier required, but ${tree.show} found", tree.pos)
+    tree match {
+      case _: Ident if !isWildcardArg(tree) =>
+        if (!tree.tpe.isStable) error
+      case _: Select =>
+        if (!tree.tpe.isStable) error
+      case _: Apply =>
+        error
+      case _ =>
+    }
   }
 
   /** The this-type of `cls` which should be used when looking at the types of

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

@@ -2453,7 +2453,7 @@ class Typer extends Namer
     */
   protected def checkEqualityEvidence(tree: tpd.Tree, pt: Type)(implicit ctx: Context) : Unit = {
     tree match {
-      case _: RefTree | _: Literal | _: Apply
+      case _: RefTree | _: Literal
         if !isVarPattern(tree) &&
           !(tree.tpe <:< pt) (ctx.addMode(Mode.GADTflexible)) =>
         val cmp =

tests/neg/i1846.scala

@@ -13,7 +13,6 @@ object Test {
     x match { case Y                => () } // error
     x match { case { Y.toInt }      => () } // error
     x match { case { Y }.toInt      => () } // error
-    x match { case Y.toString       => () } // error
     x match { case { Y }.toString   => () } // error
     x match { case { Y.toString }   => () } // error
   }

tests/neg/i3812b.scala

@@ -10,6 +10,7 @@ object Test {
 
     x match { case Y1                => () } // error
     x match { case Y2.toInt          => () } // error
+    x match { case Y1.toString       => () } // error
 
     x match { case Z1.v              => () } // error
     x match { case Z2.v              => () } // ok