merge fixes: extract typedCase to be reused in TreeChecker.

Author: DarkDimius

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

@@ -618,24 +618,25 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       accu(Set.empty, selType)
     }
 
-    def typedCase(tree: untpd.CaseDef): CaseDef = track("typedCase") {
-      def caseRest(pat: Tree)(implicit ctx: Context) = {
-        gadtSyms foreach (_.resetGADTFlexType)
-        pat foreachSubTree {
-          case b: Bind =>
-            if (ctx.scope.lookup(b.name) == NoSymbol) ctx.enter(b.symbol)
-            else ctx.error(d"duplicate pattern variable: ${b.name}", b.pos)
-          case _ =>
-        }
-        val guard1 = typedExpr(tree.guard, defn.BooleanType)
-        val body1 = typedExpr(tree.body, pt)
-        assignType(cpy.CaseDef(tree)(pat, guard1, body1), body1)
+    cases mapconserve (typedCase(_, pt, selType, gadtSyms))
+  }
+
+  def typedCase(tree: untpd.CaseDef, pt: Type, selType: Type, gadtSyms: Set[Symbol])(implicit ctx: Context): CaseDef = track("typedCase") {
+    def caseRest(pat: Tree)(implicit ctx: Context) = {
+      gadtSyms foreach (_.resetGADTFlexType)
+      pat foreachSubTree {
+        case b: Bind =>
+          if (ctx.scope.lookup(b.name) == NoSymbol) ctx.enter(b.symbol)
+          else ctx.error(d"duplicate pattern variable: ${b.name}", b.pos)
+        case _ =>
       }
-      val doCase: () => CaseDef =
-        () => caseRest(typedPattern(tree.pat, selType))(ctx.fresh.setNewScope)
-      (doCase /: gadtSyms)((op, tsym) => tsym.withGADTFlexType(op))()
+      val guard1 = typedExpr(tree.guard, defn.BooleanType)
+      val body1 = typedExpr(tree.body, pt)
+      assignType(cpy.CaseDef(tree)(pat, guard1, body1), body1)
     }
-    cases mapconserve typedCase
+    val doCase: () => CaseDef =
+      () => caseRest(typedPattern(tree.pat, selType))(ctx.fresh.setNewScope)
+    (doCase /: gadtSyms)((op, tsym) => tsym.withGADTFlexType(op))()
   }
 
   def typedReturn(tree: untpd.Return)(implicit ctx: Context): Return = track("typedReturn") {