fix and test return behavior

benchmarks/wasm/return.wat

@@ -1,13 +1,13 @@
 (module
-  (type (;0;) (func))
-  (func (;0;) (type 0)
-    block ;; label = @1
+  (func (result i32)
+    block
+      i32.const 42
       return
     end
-    unreachable
   )
-  (func (;1;) (type 0)
+  (func (result i32)
     call 0
+    unreachable
   )
   (start 1)
-)
+)

src/main/scala/wasm/MiniWasm.scala

@@ -7,6 +7,8 @@ import gensym.wasm.memory._
 import scala.collection.mutable.ArrayBuffer
 import scala.collection.mutable.HashMap
 
+case class Trap() extends Exception
+
 case class ModuleInstance(
     types: List[FuncType],
     funcs: HashMap[Int, WIR],
@@ -259,7 +261,7 @@ object Evaluator {
         eval(rest, I32V(value) :: newStack, frame, kont, trail, ret)
       case Nop =>
         eval(rest, stack, frame, kont, trail, ret)
-      case Unreachable => throw new RuntimeException("Unreachable")
+      case Unreachable => throw Trap()
       case Block(ty, inner) =>
         val k: Cont[Ans] = (retStack) =>
           eval(rest, retStack.take(ty.toList.size) ++ stack, frame, kont, trail, ret)
@@ -302,7 +304,7 @@ object Evaluator {
           eval(rest, retStack.take(ty.out.size) ++ newStack, frame, kont, trail, ret)
         // We push newK on the trail since function creates a new block to escape
         // (more or less like `return`)
-        eval(body, List(), newFrame, newK, newK :: trail, ret+1)
+        eval(body, List(), newFrame, newK, newK :: trail, 0)
       case Call(f) if frame.module.funcs(f).isInstanceOf[Import] =>
         frame.module.funcs(f) match {
           case Import("console", "log", _) =>

src/test/scala/genwasym/TestEval.scala

@@ -40,11 +40,16 @@ class TestEval extends FunSuite {
   test("fact") { testFile("./benchmarks/wasm/fact.wat", None, Some(120)) }
   test("loop") { testFile("./benchmarks/wasm/loop.wat", None, Some(10)) }
   test("even-odd") { testFile("./benchmarks/wasm/even_odd.wat", None, Some(1)) }
-  test("return") { testFile("./benchmarks/wasm/return.wat", None, None) }
   test("load") { testFile("./benchmarks/wasm/load.wat", None, Some(1)) }
   test("btree") { testFile("./benchmarks/wasm/btree/2o1u-unlabeled.wat") }
   test("fib") { testFile("./benchmarks/wasm/fib.wat", None, Some(144)) }
   test("tribonacci") { testFile("./benchmarks/wasm/tribonacci.wat", None, Some(504)) }
 
+  test("return") {
+    intercept[gensym.wasm.miniwasm.Trap] {
+      testFile("./benchmarks/wasm/return.wat", None, None)
+    }
+  }
+
   // TODO: add wasm spec tests? How to utilize wast files?
 }