Fix #3916: Fix interpretation of boxed value classes

Author: nicolasstucki

compiler/src/dotty/tools/dotc/interpreter/Interpreter.scala

@@ -117,11 +117,15 @@ class Interpreter(implicit ctx: Context) {
       case Typed(expr, _) =>
         interpretTreeImpl(expr, env)
 
-      // Getting the underlying value of a value class. The value class is evaluated as its boxed representation
-      // as values in the interpreter are `Object`s. Therefore we just get it from the enviroment as is.
-      case Select(qualifier, _)
+      case Select(qualifier, name)
           if tree.symbol.owner.isValueClass && tree.symbol.is(ParamAccessor) && env.contains(qualifier.symbol) =>
-        env(qualifier.symbol)
+        val value = env(qualifier.symbol)
+        val clazz = value.getClass
+        if (clazz.getCanonicalName != tree.symbol.owner.showFullName) value // Already unboxed
+        else {
+          val method = getMethod(clazz, name, Nil)
+          interpreted(method.invoke(value))
+        }
 
       case SeqLiteral(elems, _) =>
         elems.map(elem => interpretTreeImpl(elem, env))

tests/pos/i3916/Macro_1.scala

@@ -0,0 +1,21 @@
+import scala.quoted._
+
+class FInterpolatorHelper(val sc: StringContext) extends AnyVal {
+  inline def ff(arg1: Any): String = ~FInterpolation.fInterpolation(sc, Seq('(arg1)))
+  inline def ff(arg1: Any, arg2: Any): String = ~FInterpolation.fInterpolation(sc, Seq('(arg1), '(arg2)))
+  inline def ff(arg1: Any, arg2: Any, arg3: Any): String = ~FInterpolation.fInterpolation(sc, Seq('(arg1), '(arg2), '(arg3)))
+  // ...
+}
+
+object FInterpolation {
+  private def liftSeq(args: Seq[Expr[Any]]): Expr[Seq[Any]] = args match {
+    case x :: xs  => '{ (~x) +: ~(liftSeq(xs))  }
+    case Nil => '(Seq(): Seq[Any])
+  }
+
+  def fInterpolation(sc: StringContext, args: Seq[Expr[Any]]): Expr[String] = {
+    val str: Expr[String] = sc.parts.mkString("")
+    val args1: Expr[Seq[Any]] = liftSeq(args)
+    '{  (~str).format(~args1: _*) }
+  }
+}

tests/pos/i3916/Test_2.scala

@@ -0,0 +1,5 @@
+ object Test {
+  def main(args: Array[String]): Unit = {
+    println(new FInterpolatorHelper(StringContext("hello%s")).ff(5))
+  }
+}