Fix #9802: Interpret by-name params as () => interpret(arg)

Author: nicolasstucki

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

@@ -250,7 +250,7 @@ object Splicer {
           interpretModuleAccess(fn.symbol)
         else if (fn.symbol.is(Method) && fn.symbol.isStatic) {
           val staticMethodCall = interpretedStaticMethodCall(fn.symbol.owner, fn.symbol)
-          staticMethodCall(args.flatten.map(interpretTree))
+          staticMethodCall(interpretArgs(args, fn.symbol.info))
         }
         else if fn.symbol.isStatic then
           assert(args.isEmpty)
@@ -260,7 +260,7 @@ object Splicer {
             interpretModuleAccess(fn.qualifier.symbol)
           else {
             val staticMethodCall = interpretedStaticMethodCall(fn.qualifier.symbol.moduleClass, fn.symbol)
-            staticMethodCall(args.flatten.map(interpretTree))
+            staticMethodCall(interpretArgs(args, fn.symbol.info))
           }
         else if (env.contains(fn.symbol))
           env(fn.symbol)
@@ -289,6 +289,24 @@ object Splicer {
         unexpectedTree(tree)
     }
 
+    private def interpretArgs(argss: List[List[Tree]], fnType: Type)(using Env): List[Object] = {
+      fnType match
+        case fnType: PolyType => interpretArgs(argss, fnType.resType)
+        case fnType: MethodType if fnType.isErasedMethod => interpretArgs(argss, fnType.resType)
+        case fnType: MethodType =>
+          val interprededHeadParams =
+            for (info, arg) <- fnType.paramInfos.lazyZip(argss.head) yield
+              info match
+                case _: ExprType => () => interpretTree(arg) // by-name argument
+                case _ => interpretTree(arg) // by-value argument
+          interprededHeadParams.toList ::: interpretArgs(argss.tail, fnType.resType)
+        case _ =>
+          // If the final result type is a context function the rest of the args are interpreted as by-value.
+          // for  `def f(x: Int): Int ?=> Int` we call directly the verison that does not create the closure
+          // `def f$direct(x: Int)(x$1: Int): Int`.
+          argss.flatMap(_.map(interpretTree))
+    }
+
     private def interpretBlock(stats: List[Tree], expr: Tree)(implicit env: Env) = {
       var unexpected: Option[Object] = None
       val newEnv = stats.foldLeft(env)((accEnv, stat) => stat match {

tests/pos-macros/i9802/Macro_1.scala

@@ -0,0 +1,5 @@
+import scala.quoted._
+
+inline def fun(inline prog: Double): Double = ${impl('prog)}
+
+def impl(prog: => Expr[Double])(using QuoteContext) : Expr[Double] = '{ 42.0 }

tests/pos-macros/i9802/Test_2.scala

@@ -0,0 +1,2 @@
+
+def test: Unit = fun(4)