[js-api][test] Refine DefaultValue for new reference types

DefaultValue will return undefined for externref as before, but
for other nullable reference types will return null.

For non-nullable reference types, operations like grow and set
should error if the value to set is missing.

Also adds WPT tests for the error cases. This requires some
updates to wasm-module-builder.js as well.

Fixes issue WebAssembly#501

document/core/appendix/embedding.rst

@@ -693,3 +693,23 @@ Matching
    \F{match\_externtype}(\X{et}_1, \X{et}_2) &=& \TRUE && (\iff \vdashexterntypematch \X{et}_1 \matchesexterntype \X{et}_2) \\
    \F{match\_externtype}(\X{et}_1, \X{et}_2) &=& \FALSE && (\otherwise) \\
    \end{array}
+
+
+.. index:: value type
+.. _embed-default-value:
+
+Value types
+~~~~~~~~~~~
+
+:math:`\F{default\_value}(\type) : \val`
+...............................................
+
+1. If :math:`\default_{type}` is not defined, then return :math:`\ERROR`.
+
+1. Else, return the :ref:`value <syntax-val>` :math:`\default_{type}`.
+
+.. math::
+   \begin{array}{lclll}
+   \F{default\_value}(t) &=& v && (\iff \default_t = v) \\
+   \F{default\_value}(t) &=& \ERROR && (\iff \default_t = \epsilon) \\
+   \end{array}

document/js-api/index.bs

@@ -116,6 +116,7 @@ urlPrefix: https://webassembly.github.io/spec/core/; spec: WebAssembly; type: df
     text: global_write; url: appendix/embedding.html#embed-global-write
     text: ref_type; url: appendix/embedding.html#embed-ref-type
     text: match_valtype; url: appendix/embedding.html#embed-match-valtype
+    text: default_value; url: appendix/embedding.html#embed-default-value
     text: error; url: appendix/embedding.html#embed-error
     text: store; url: exec/runtime.html#syntax-store
     text: table type; url: syntax/types.html#syntax-tabletype
@@ -764,6 +765,7 @@ Each {{Table}} object has a \[[Table]] internal slot, which is a [=table address
     1. If |maximum| is not empty and |maximum| < |initial|, throw a {{RangeError}} exception.
     1. If |value| is missing,
         1. Let |ref| be [=DefaultValue=](|elementType|).
+        1. Assert: |ref| is not [=error=].
     1. Otherwise,
         1. Let |ref| be [=?=] [=ToWebAssemblyValue=](|value|, |elementType|).
     1. Let |type| be the [=table type=] {[=table type|min=] |initial|, [=table type|max=] |maximum|} |elementType|.
@@ -781,6 +783,7 @@ Each {{Table}} object has a \[[Table]] internal slot, which is a [=table address
     1. Let (<var ignore>limits</var>, |elementType|) be [=table_type=](|tableaddr|).
     1. If |value| is missing,
         1. Let |ref| be [=DefaultValue=](|elementType|).
+        1. If |ref| is [=error=], throw a {{TypeError}} exception.
     1. Otherwise,
         1. Let |ref| be [=?=] [=ToWebAssemblyValue=](|value|, |elementType|).
     1. Let |result| be [=table_grow=](|store|, |tableaddr|, |delta|, |ref|).
@@ -814,6 +817,7 @@ Each {{Table}} object has a \[[Table]] internal slot, which is a [=table address
     1. Let (<var ignore>limits</var>, |elementType|) be [=table_type=](|tableaddr|).
     1. If |value| is missing,
         1. Let |ref| be [=DefaultValue=](|elementType|).
+        1. If |ref| is [=error=], throw a {{TypeError}} exception.
     1. Otherwise,
         1. Let |ref| be [=?=] [=ToWebAssemblyValue=](|value|, |elementType|).
     1. Let |store| be the [=surrounding agent=]'s [=associated store=].
@@ -890,13 +894,8 @@ which can be simultaneously referenced by multiple {{Instance}} objects. Each
 
 <div algorithm>
     The algorithm <dfn>DefaultValue</dfn>(|valuetype|) performs the following steps:
-    1. If |valuetype| equals [=i32=], return [=i32.const=] 0.
-    1. If |valuetype| equals [=i64=], return [=i64.const=] 0.
-    1. If |valuetype| equals [=f32=], return [=f32.const=] 0.
-    1. If |valuetype| equals [=f64=], return [=f64.const=] 0.
-    1. If |valuetype| equals [=funcref=], return [=ref.null=] [=funcref=].
     1. If |valuetype| equals [=externref=], return [=ToWebAssemblyValue=](undefined, |valuetype|).
-    1. Assert: This step is not reached.
+    1. Return [=default_value=](|valuetype|).
 </div>
 
 <div algorithm>
@@ -907,6 +906,7 @@ which can be simultaneously referenced by multiple {{Instance}} objects. Each
         1. Throw a {{TypeError}} exception.
     1. If |v| is missing,
         1. Let |value| be [=DefaultValue=](|valuetype|).
+        1. Assert: |value| is not [=error=].
     1. Otherwise,
         1. Let |value| be [=ToWebAssemblyValue=](|v|, |valuetype|).
     1. If |mutable| is true, let |globaltype| be [=var=] |valuetype|; otherwise, let |globaltype| be [=const=] |valuetype|.

test/js-api/gc/default-value.tentative.any.js

@@ -0,0 +1,43 @@
+// META: global=window,dedicatedworker,jsshell
+// META: script=/wasm/jsapi/wasm-module-builder.js
+
+let exports = {};
+setup(() => {
+  const builder = new WasmModuleBuilder();
+
+  builder.addTable(wasmRefType(kWasmAnyRef), 10, 20, [...wasmI32Const(42), ...GCInstr(kExprRefI31)])
+    .exportAs("tableAnyNonNullable");
+  builder.addTable(wasmRefNullType(kWasmAnyRef), 10, 20)
+    .exportAs("tableAnyNullable");
+
+  const buffer = builder.toBuffer();
+  const module = new WebAssembly.Module(buffer);
+  const instance = new WebAssembly.Instance(module, {});
+  exports = instance.exports;
+});
+
+test(() => {
+  exports.tableAnyNullable.grow(5);
+  for (let i = 0; i < 5; i++)
+    assert_equals(exports.tableAnyNullable.get(10 + i), null);
+}, "grow (nullable anyref)");
+
+test(() => {
+  assert_throws_js(TypeError, () => { exports.tableAnyNonNullable.grow(5); });
+  exports.tableAnyNonNullable.grow(5, "foo");
+  for (let i = 0; i < 5; i++)
+    assert_equals(exports.tableAnyNonNullable.get(10 + i), "foo");
+}, "grow (non-nullable anyref)");
+
+test(() => {
+  for (let i = 0; i < exports.tableAnyNullable.length; i++) {
+    exports.tableAnyNullable.set(i);
+    assert_equals(exports.tableAnyNullable.get(i), null);
+  }
+}, "set (nullable anyref)");
+
+test(() => {
+  for (let i = 0; i < exports.tableAnyNonNullable.length; i++) {
+    assert_throws_js(TypeError, () => { exports.tableAnyNonNullable.set(i); });
+  }
+}, "set (non-nullable anyref)");

test/js-api/gc/i31.tentative.any.js

@@ -11,7 +11,7 @@ setup(() => {
   builder
     .addFunction("makeI31", makeSig_r_x(i31Ref, kWasmI32))
     .addBody([kExprLocalGet, 0,
-              ...GCInstr(kExprI31New)])
+              ...GCInstr(kExprRefI31)])
     .exportFunc();
 
   builder
@@ -33,7 +33,7 @@ setup(() => {
     .exportFunc();
 
   builder
-    .addGlobal(i31NullableRef, true, [...wasmI32Const(0), ...GCInstr(kExprI31New)])
+    .addGlobal(i31NullableRef, true, [...wasmI32Const(0), ...GCInstr(kExprRefI31)])
   builder
     .addExportOfKind("i31Global", kExternalGlobal, 0);
 

test/js-api/wasm-module-builder.js

@@ -456,7 +456,7 @@ let kExprBrOnCast = 0x18;
 let kExprBrOnCastFail = 0x19;
 let kExprExternInternalize = 0x1a;
 let kExprExternExternalize = 0x1b;
-let kExprI31New = 0x1c;
+let kExprRefI31 = 0x1c;
 let kExprI31GetS = 0x1d;
 let kExprI31GetU = 0x1e;
 
@@ -1199,6 +1199,10 @@ class WasmModuleBuilder {
       binary.emit_section(kTableSectionCode, section => {
         section.emit_u32v(wasm.tables.length);
         for (let table of wasm.tables) {
+          if (table.has_init) {
+            section.emit_u8(0x40);  // "has initializer"
+            section.emit_u8(0x00);  // Reserved byte.
+          }
           section.emit_type(table.type);
           section.emit_u8(table.has_max);
           section.emit_u32v(table.initial_size);