Suppress inline checking after erasure

After erasure, the rhs of an inline val like

    inline val n = 3

no longer has a constant type. Therefore, we need to disable
the check for it after erasure. Test case (discovered by
accident) in harmonize.scala.

Author: odersky

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

@@ -557,7 +557,8 @@ trait Checking {
       case tp => tp.widenTermRefExpr match {
         case tp: ConstantType if isPureExpr(tree) => // ok
         case tp if defn.isFunctionType(tp) && isPureExpr(tree) => // ok
-        case _ => ctx.error(em"$what must be a constant expression or a function", tree.pos)
+        case _ =>
+          if (!ctx.erasedTypes) ctx.error(em"$what must be a constant expression or a function", tree.pos)
       }
     }
 

tests/pos/harmonize.scala

@@ -3,25 +3,40 @@ object Test {
   def main(args: Array[String]) = {
     val x = true
     val n = 1
+    inline val nn = 2
     val y = if (x) 'A' else n
     val z: Int = y
 
-    val yy = n match {
+    val yy1 = n match {
       case 1 => 'A'
       case 2 => n
       case 3 => 1.0
     }
-    val zz: Double = yy
+    val zz1: AnyVal = yy1 // no widening
+
+    val yy2 = n match {
+      case 1 => 'A'
+      case 2 => nn
+      case 3 => 1.0f
+    }
+    val zz2: Float = yy2 // widening to Float
+
+    val yy3 = n match {
+      case 1 => 'A'
+      case 2 => 3L
+      case 3 => 1.0f
+    }
+    val zz3: Double = yy3 // widening to Double
 
     val a = try {
       'A'
     } catch {
-      case ex: Exception => n
+      case ex: Exception => nn
       case ex: Error => 3L
     }
     val b: Long = a
 
-    val xs = List(1.0, n, 'c')
+    val xs = List(1.0, nn, 'c')
     val ys: List[Double] = xs
   }