Move checks on symbol falgs and types to Checking

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/UnusedChecks.scala

@@ -24,27 +24,17 @@ class UnusedChecks extends MiniPhase {
 
   /* Tree transform */
 
-  override def transformTypeDef(tree: TypeDef)(implicit ctx: Context): tree.type = {
-    if (tree.symbol.is(UnusedType))
-      ctx.error(tree.symbol.showKind + " cannot be unused", tree.pos)
-    tree
-  }
-
   override def transformApply(tree: Apply)(implicit ctx: Context): tree.type = {
     if (!isUnusedContext && !tree.symbol.is(Unused) && !tree.fun.tpe.widen.isUnusedMethod)
       tree.args.foreach(arg => checked(arg)(arg, "Cannot use `unused` value in a context that is not `unused`"))
     tree
   }
 
   override def transformDefDef(tree: DefDef)(implicit ctx: Context): tree.type = {
-    checkUnusedNothing(tree)
     checkedValOrDefDefRHS(tree)
   }
 
   override def transformValDef(tree: ValDef)(implicit ctx: Context): tree.type = {
-    checkUnusedNothing(tree)
-    if (tree.symbol.is(Unused) && tree.symbol.is(MutableOrLazy))
-      ctx.error(tree.symbol.showKind + " cannot be unused", tree.pos)
     checkedValOrDefDefRHS(tree)
   }
 
@@ -66,12 +56,6 @@ class UnusedChecks extends MiniPhase {
 
   /* private methods */
 
-  /** Check that unused values are not of type Nothing */
-  private def checkUnusedNothing(tree: Tree)(implicit ctx: Context): Unit = {
-    if (tree.symbol.is(Unused) && tree.tpe.widen.finalResultType.isBottomType)
-      ctx.error("unused " + tree.symbol.showKind + " cannot have type Nothing", tree.pos)
-  }
-
   /** Check that the expression is not a reference to an unused value */
   private def checkedValOrDefDefRHS(tree: ValOrDefDef)(implicit ctx: Context): tree.type =
     if (tree.symbol.is(Unused)) tree

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

@@ -377,6 +377,12 @@ object Checking {
         fail(CannotHaveSameNameAs(sym, cls, CannotHaveSameNameAs.CannotBeOverridden))
         sym.setFlag(Private) // break the overriding relationship by making sym Private
       }
+    checkApplicable(UnusedType, !sym.is(UnusedType))
+    if (sym.is(Unused)) {
+      checkApplicable(Unused, !sym.is(MutableOrLazy))
+      if (sym.info.widen.finalResultType.isBottomType)
+        fail("unused " + sym.showKind + " cannot have type Nothing")
+    }
   }
 
   /** Check the type signature of the symbol `M` defined by `tree` does not refer