[spec] Normative: Add i64<->BigInt conversion in JS API

With this patch, BigInts have support for bidirectionally converting
to 64-bit integer WebAssembly values, which appears as
- Parameters and return values to exported WebAssembly functions
- Parameters and return values to host functions
- Imported and exported globals

BigInts can be read or written from WebAssembly memory using the
BigInt proposal's BigInt64Array or BigUint64Array; no additional
support is needed.

This patch includes basic conformance tests in jsapi.js, which tests
that the conversion is done properly in the six cases listed above.
I don't know of any Wasm implementation that attempts to implement
this specification, so I converted most of the test to be against
i32 and saw that converted version pass on V8 (this process helped
work out a few silly test bugs).

Closes WebAssembly/design#1172

document/js-api/index.bs

@@ -20,6 +20,12 @@ Prepare For TR: true
     "title": "WebAssembly Core Specification",
     "publisher": "W3C WebAssembly Community Group",
     "status": "Draft"
+  },
+  "BIGINT": {
+    "href": "https://tc39.github.io/proposal-bigint/",
+    "title": "BigInt Specification",
+    "publisher": "TC39",
+    "status": "Stage 3 proposal"
   }
 }
 </pre>
@@ -160,11 +166,18 @@ urlPrefix: https://webassembly.github.io/spec/core/; spec: WebAssembly; type: df
         text: var
         text: const
     text: address; url: exec/runtime.html#addresses
+<<<<<<< HEAD
     text: signed_32; url: exec/numerics.html#aux-signed
     text: grow_memory; url: exec/instructions.html#exec-grow-memory
     text: current frame; url: exec/conventions.html#exec-notation-textual
     text: 𝗆𝗈𝖽𝗎𝗅𝖾; url: exec/runtime.html#syntax-frame
     text: 𝗆𝖾𝗆𝖺𝖽𝖽𝗋𝗌; url: exec/runtime.html#syntax-moduleinst
+=======
+    text: signed_64; url: exec/numerics.html#aux-signed
+urlPrefix: https://tc39.github.io/proposal-bigint/; spec: BIGINT; type: dfn
+    text: ToBigInt64; url: #sec-to-big-int64
+    text: BigInt; url: #sec-ecmascript-language-types-bigint-type
+>>>>>>> [spec] Normative: Add i64<->BigInt conversion in JS API
 </pre>
 
 <pre class='link-defaults'>
@@ -334,6 +347,7 @@ A {{Module}} object represents a single WebAssembly module. Each {{Module}} obje
                 1. Let |index| be the number of external functions in |imports|. This value |index| is known as the <dfn>index of the host function</dfn> |funcaddr|.
             1. Let |externfunc| be the [=external value=] [=external value|𝖿𝗎𝗇𝖼=] |funcaddr|.
             1. [=Append=] |externfunc| to |imports|.
+<<<<<<< HEAD
         1. If |externtype| is of the form [=𝗀𝗅𝗈𝖻𝖺𝗅=] <var ignore>mut</var> |valtype|,
             1. If [=Type=](|v|) is [=Number=],
                 1. If |valtype| is [=𝗂𝟨𝟦=], throw a {{LinkError}} exception.
@@ -345,6 +359,14 @@ A {{Module}} object represents a single WebAssembly module. Each {{Module}} obje
                 1. Let |globaladdr| be |v|.\[[Global]]
             1. Otherwise,
                 1. Throw a {{LinkError}} exception.
+=======
+        1. If |externtype| is of the form [=𝗀𝗅𝗈𝖻𝖺𝗅=] |globaltype|,
+            1. Let |value| be [=ToWebAssemblyValue=](|v|, |globaltype|.<em>[=global type|valtype=]</em>)
+            1. Assert: |globaltype|.<em>[=global type|mut=]</em> is [=global type|𝖼𝗈𝗇𝗌𝗍=], as verified by WebAssembly validation.
+            1. Let |store| be the [=surrounding agent=]'s [=associated store=].
+            1. Let (|store|, |globaladdr|) be [=alloc_global=](|store|, |globaltype|, |value|).
+            1. Set the [=surrounding agent=]'s [=associated store=] to |store|.
+>>>>>>> [spec] Normative: Add i64<->BigInt conversion in JS API
             1. Let |externglobal| be [=external value|𝗀𝗅𝗈𝖻𝖺𝗅=] |globaladdr|.
             1. [=Append=] |externglobal| to |imports|.
         1. If |externtype| is of the form [=𝗆𝖾𝗆=] |memtype|,
@@ -376,7 +398,12 @@ A {{Module}} object represents a single WebAssembly module. Each {{Module}} obje
             1. Let [=external value|𝖿𝗎𝗇𝖼=] |funcaddr| be |externval|.
             1. Let |func| be the result of creating [=a new Exported Function=] from |funcaddr|.
             1. Let |value| be |func|.
+<<<<<<< HEAD
         1. If |externtype| is of the form [=𝗀𝗅𝗈𝖻𝖺𝗅=] <var ignore>globaltype</var>,
+=======
+        1. If |externtype| is of the form [=𝗀𝗅𝗈𝖻𝖺𝗅=] |globaltype|,
+            1. Assert: |globaltype|.<em>[=global type|mut=]</em> is [=global type|𝖼𝗈𝗇𝗌𝗍=], as verified by WebAssembly validation.
+>>>>>>> [spec] Normative: Add i64<->BigInt conversion in JS API
             1. Assert: |externval| is of the form [=external value|𝗀𝗅𝗈𝖻𝖺𝗅=] |globaladdr|.
             1. Let [=external value|𝗀𝗅𝗈𝖻𝖺𝗅=] |globaladdr| be |externval|.
             1. Let |global| be [=create a global object|a new Global object=] created from |globaladdr|.
@@ -875,10 +902,6 @@ This slot holds a [=function address=] relative to the [=surrounding agent=]'s [
     1. Let |store| be the [=surrounding agent=]'s [=associated store=].
     1. Let |functype| be [=type_func=](|store|, |funcaddr|).
     1. Let [|parameters|] → [|results|] be |functype|.
-    1. If |parameters| or |results| contains an [=𝗂𝟨𝟦=], throw a {{TypeError}}.
-
-        Note: the above error is thrown each time the \[[Call]] method is invoked.
-
     5. Let |args| be an empty list of WebAssembly values.
     1. Let |i| be 0.
     1. For each type |t| of |parameters|,
@@ -901,7 +924,6 @@ Note: Exported Functions do not have a \[[Construct]] method and thus it is not
   To <dfn>create a host function</dfn> from the JavaScript object |func|, perform the following steps:
 
     1. Let |hostfunc| be a [=host function=] which performs the following steps when called:
-        1. If the signature contains an [=𝗂𝟨𝟦=] (as argument or result), the host function throws a {{TypeError}} when called.
         1. Let |arguments| be a [=list=] of the arguments of the invocation of this function.
         1. Let |jsArguments| be an empty [=list=].
         1. For each |arg| in |arguments|,
@@ -919,10 +941,19 @@ Note: Exported Functions do not have a \[[Construct]] method and thus it is not
 <div algorithm>
 The algorithm <dfn>ToJSValue</dfn>(|w|) coerces a [=WebAssembly value=] to a JavaScript value performs the following steps:
 
+<<<<<<< HEAD
 1. Assert: |w| is not of the form [=𝗂𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] <var ignore>i64</var>.
 1. If |w| is of the form [=𝗂𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] |i32|, return [=the Number value=] for [=signed_32=](|i32|).
 1. If |w| is of the form [=𝖿𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] |f32|, return [=the Number value=] for |f32|.
 1. If |w| is of the form [=𝖿𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] |f64|, return [=the Number value=] for |f64|.
+=======
+1. If |w| is of the form [=𝗂𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] |i64|,
+    1. Let |v| be [=signed_64=](|i64|).
+    1. Return a [=BigInt=] representing the mathematical value |v|.
+1. If |w| is of the form [=𝗂𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] |i32|, return [=the Number value=] of |i32|.
+1. If |w| is of the form [=𝖿𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] |f32|, return [=the Number value=] of |f32|.
+1. If |w| is of the form [=𝖿𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] |f64|, return [=the Number value=] of |f64|.
+>>>>>>> [spec] Normative: Add i64<->BigInt conversion in JS API
 
 <!-- If the WebAssembly value is optional, then given `None`, return JavaScript value `undefined`. -->
 
@@ -933,7 +964,13 @@ Note: Number values which are equal to NaN may have various observable NaN paylo
 The algorithm <dfn>ToWebAssemblyValue</dfn>(|v|, |type|) coerce a JavaScript value to a [=WebAssembly value=]  performs the following steps:
 
 
+<<<<<<< HEAD
 1. Assert: |type| is not [=𝗂𝟨𝟦=].
+=======
+1. If |type| is [=𝗂𝟨𝟦=],
+    1. Let |i64| be [=ToBigInt64=](|v|).
+    1. Return [=𝗂𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] |i64|.
+>>>>>>> [spec] Normative: Add i64<->BigInt conversion in JS API
 1. If |type| is [=𝗂𝟥𝟤=],
     1. Let |i32| be ? [=ToInt32=](|v|).
     1. Return [=𝗂𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] |i32|.