Pass by name should not introduce boxing

Author: Duhemm

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -69,14 +69,14 @@ class Compiler {
            new ExplicitSelf,        // Make references to non-trivial self types explicit as casts
            new ShortcutImplicits,   // Allow implicit functions without creating closures
            new CrossCastAnd,        // Normalize selections involving intersection types.
-           new Splitter,            // Expand selections involving union types into conditionals
-           new SpecializeFunctions), // Specialized Function1 by replacing super with specialized super
+           new Splitter),           // Expand selections involving union types into conditionals
       List(new PhantomArgLift, // Extracts the evaluation of phantom arguments placing them before the call.
            new VCInlineMethods,     // Inlines calls to value class methods
            new SeqLiterals,         // Express vararg arguments as arrays
            new InterceptedMethods,  // Special handling of `==`, `|=`, `getClass` methods
            new Getters,             // Replace non-private vals and vars with getter defs (fields are added later)
-           new ElimByName,          // Expand by-name parameter references
+           new ElimByName),         // Expand by-name parameter references
+      List(new SpecializeFunctions, // Specialized Function{0,1,2} by replacing super with specialized super
            new ElimOuterSelect,     // Expand outer selections
            new AugmentScala2Traits, // Expand traits defined in Scala 2.x to simulate old-style rewritings
            new ResolveSuper,        // Implement super accessors and add forwarders to trait methods

compiler/test/dotty/tools/dotc/transform/SpecializeFunctionsTests.scala

@@ -214,4 +214,16 @@ class SpecializeFunctionsTests extends DottyBytecodeTest {
       assertBoxing("<init>", findClass("Test$", dir).methods)
     }
   }
+
+  @Test def passByNameNoBoxing = {
+    implicit val source: String =
+      """|object Test {
+         |  def fn(x: => Int): Int = x
+         |  fn(2)
+         |}""".stripMargin
+
+    checkBCode(source) { dir =>
+      assertNoBoxing("fn", findClass("Test$", dir).methods)
+    }
+  }
 }