Refine handling of inline parameters of macros

These are at runtime trees with constant types. We can extract the constant
from the tree, so they can also be used in a splicing context.

Author: odersky

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

@@ -173,6 +173,19 @@ class ReifyQuotes extends MacroTransform {
       case _ =>
     }
 
+    /** Does the level of `sym` match the current level?
+     *  An exception is made for inline vals in macros. These are also OK if their level
+     *  is one higher than the current level, because on execution such values
+     *  are constant expression trees and we can pull out the constant from the tree.
+     */
+    def levelOK(sym: Symbol)(implicit ctx: Context): Boolean = levelOf.get(sym) match {
+      case Some(l) =>
+        l == level ||
+        sym.is(Inline) && sym.owner.is(Macro) && sym.info.isValueType && l - 1 == level
+      case None =>
+        true
+    }
+
     /** Issue a "splice outside quote" error unless we ar in the body of an inline method */
     def spliceOutsideQuotes(pos: Position)(implicit ctx: Context) =
       ctx.error(i"splice outside quotes", pos)
@@ -188,7 +201,7 @@ class ReifyQuotes extends MacroTransform {
         else i"${sym.name}.this"
       if (!isThis && sym.maybeOwner.isType)
         check(sym.owner, sym.owner.thisType, pos)
-      else if (sym.exists && !sym.isStaticOwner && levelOf.getOrElse(sym, level) != level)
+      else if (sym.exists && !sym.isStaticOwner && !levelOK(sym))
         tp match {
           case tp: TypeRef =>
             importedTypes += tp
@@ -329,7 +342,7 @@ class ReifyQuotes extends MacroTransform {
             cpy.Select(expansion)(cpy.Inlined(tree)(call, bindings, body), name)
           case _: Import =>
             tree
-          case tree: DefDef if tree.symbol.is(Macro) =>
+          case tree: DefDef if tree.symbol.is(Macro) && level == 0 =>
             val tree1 = nested(isQuote = true).transform(tree)
               // check macro code as it if appeared in a quoted context
             cpy.DefDef(tree)(rhs = EmptyTree)

tests/neg/inlinevals.scala

@@ -17,6 +17,12 @@ object Test {
 
   inline val M = X  // error: rhs must be constant expression
 
+  inline val xs = List(1, 2, 3) // error: must be a constant expression
+
+  def f(inline xs: List[Int]) = xs
+
+  f(List(1, 2, 3)) // error: must be a constant expression
+
   def byname(inline f: => String): Int = ??? // ok
 
   byname("hello" ++ " world")

tests/pos/quoted.scala

@@ -10,6 +10,13 @@ class Test {
     def assertImpl(expr: Expr[Boolean]) =
       '{ if !(~expr) then throw new AssertionError(s"failed assertion: ${~expr}") }
 
+    inline def power(inline n: Int, x: Double) = ~powerCode(n, '(x))
+
+    def powerCode(n: Int, x: Expr[Double]): Expr[Double] =
+      if (n == 0) '(1.0)
+      else if (n == 1) x
+      else if (n % 2 == 0) '{ { val y = ~x * ~x; ~powerCode(n / 2, '(y)) } }
+      else '{ ~x * ~powerCode(n - 1, x) }
   }
 
   val program = '{
@@ -19,6 +26,12 @@ class Test {
     assert(x != 0)
 
     ~assertImpl('(x != 0))
+
+    val y = math.sqrt(2.0)
+
+    power(3, y)
+
+    ~powerCode(3, '{math.sqrt(2.0)})
   }
 
   program.run