Fix #106: Use an actual toString() call for toString() on JS value.

As opposed to using `"" + x`, which is only valid for string
concatenation.

In most cases it makes no difference. The difference can only be
observed for `symbol`s.

Author: sjrd

Diff for: build.sbt

@@ -226,8 +226,6 @@ lazy val `scalajs-test-suite` = project
 
 lazy val IgnoredTestNames: Set[String] = {
   Set(
-    // wellKnownSymbolIterator/testToString failed: scala.scalajs.js.JavaScriptException: TypeError: Cannot convert a Symbol value to a string
-    "org.scalajs.testsuite.jsinterop.SymbolTest",
     // Cannot call wasmObject.toString() from JavaScript:
     // boxValueClassesGivenToJSInteropMethod failed: scala.scalajs.js.JavaScriptException: TypeError: vc.toString is not a function
     "org.scalajs.testsuite.compiler.InteroperabilityTest",

Diff for: wasm/src/main/scala/ir2wasm/LoaderContent.scala

@@ -121,7 +121,8 @@ const scalaJSHelpers = {
   emptyString: () => "",
   stringLength: (s) => s.length,
   stringCharAt: (s, i) => s.charCodeAt(i),
-  jsValueToString: (x) => "" + x,
+  jsValueToString: (x) => (x === void 0) ? "undefined" : x.toString(),
+  jsValueToStringForConcat: (x) => "" + x,
   booleanToString: (b) => b ? "true" : "false",
   charToString: (c) => String.fromCharCode(c),
   intToString: (i) => "" + i,

Diff for: wasm/src/main/scala/ir2wasm/WasmExpressionBuilder.scala

@@ -1239,7 +1239,7 @@ private class WasmExpressionBuilder private (
             } // end block labelNotOurObject
 
             // Now we have a value that is not one of our objects; the anyref is still on the stack
-            instrs += CALL(WasmFunctionName.jsValueToString)
+            instrs += CALL(WasmFunctionName.jsValueToStringForConcat)
           } // end block labelDone
         }
       }
@@ -1264,7 +1264,7 @@ private class WasmExpressionBuilder private (
             case IRTypes.DoubleType =>
               instrs += CALL(WasmFunctionName.doubleToString)
             case IRTypes.NullType | IRTypes.UndefType =>
-              instrs += CALL(WasmFunctionName.jsValueToString)
+              instrs += CALL(WasmFunctionName.jsValueToStringForConcat)
             case IRTypes.NothingType =>
               () // unreachable
             case IRTypes.NoType =>
@@ -1276,7 +1276,7 @@ private class WasmExpressionBuilder private (
         case IRTypes.ClassType(IRNames.BoxedStringClass) =>
           // Common case for which we want to avoid the hijacked class dispatch
           genTreeAuto(tree)
-          instrs += CALL(WasmFunctionName.jsValueToString) // for `null`
+          instrs += CALL(WasmFunctionName.jsValueToStringForConcat) // for `null`
 
         case IRTypes.ClassType(className) =>
           genWithDispatch(ctx.getClassInfo(className).isAncestorOfHijackedClass)

Diff for: wasm/src/main/scala/wasm4s/Names.scala

@@ -179,7 +179,8 @@ object Names {
     val emptyString = helper("emptyString")
     val stringLength = helper("stringLength")
     val stringCharAt = helper("stringCharAt")
-    val jsValueToString = helper("jsValueToString")
+    val jsValueToString = helper("jsValueToString") // for actual toString() call
+    val jsValueToStringForConcat = helper("jsValueToStringForConcat")
     val booleanToString = helper("booleanToString")
     val charToString = helper("charToString")
     val intToString = helper("intToString")

Diff for: wasm/src/main/scala/wasm4s/WasmContext.scala

@@ -420,7 +420,8 @@ class WasmContext(val module: WasmModule) extends TypeDefinableWasmContext {
   addHelperImport(WasmFunctionName.emptyString, List(), List(WasmRefType.any))
   addHelperImport(WasmFunctionName.stringLength, List(WasmRefType.any), List(WasmInt32))
   addHelperImport(WasmFunctionName.stringCharAt, List(WasmRefType.any, WasmInt32), List(WasmInt32))
-  addHelperImport(WasmFunctionName.jsValueToString, List(anyref), List(WasmRefType.any))
+  addHelperImport(WasmFunctionName.jsValueToString, List(WasmRefType.any), List(WasmRefType.any))
+  addHelperImport(WasmFunctionName.jsValueToStringForConcat, List(anyref), List(WasmRefType.any))
   addHelperImport(WasmFunctionName.booleanToString, List(WasmInt32), List(WasmRefType.any))
   addHelperImport(WasmFunctionName.charToString, List(WasmInt32), List(WasmRefType.any))
   addHelperImport(WasmFunctionName.intToString, List(WasmInt32), List(WasmRefType.any))