[dart2wasm] Update built-in string imports according to the latest spec

Spec: https://github.com/WebAssembly/js-string-builtins

Change-Id: Idb387e6dd27b203ddca52291c44fb2aa15ee75cf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/357560
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

pkg/dart2wasm/bin/run_wasm.js

@@ -363,8 +363,20 @@ const main = async () => {
     }
 
     const dart2wasm = await import(args[jsRuntimeArg]);
-    function compile(filename) {
-        // Create a Wasm module from the binary wasm file.
+
+    /// Returns whether the `js-string` built-in is supported.
+    function detectImportedStrings() {
+        let bytes = [
+            0,   97,  115, 109, 1,   0,   0,  0,   1,   4,   1,   96,  0,
+            0,   2,   23,  1,   14,  119, 97, 115, 109, 58,  106, 115, 45,
+            115, 116, 114, 105, 110, 103, 4,  99,  97,  115, 116, 0,   0
+        ];
+        return !WebAssembly.validate(
+            new Uint8Array(bytes), {builtins: ['js-string']});
+    }
+
+    function compile(filename, withJsStringBuiltins) {
+        // Create a Wasm module from the binary Wasm file.
         var bytes;
         if (isJSC) {
           bytes = readFile(filename, "binary");
@@ -373,11 +385,10 @@ const main = async () => {
         } else {
           bytes = readRelativeToScript(filename, "binary");
         }
-        return new WebAssembly.Module(bytes);
-    }
-
-    function instantiate(filename, imports) {
-        return new WebAssembly.Instance(compile(filename), imports);
+        return WebAssembly.compile(
+            bytes,
+            withJsStringBuiltins ? {builtins: ['js-string']} : {}
+        );
     }
 
     globalThis.window ??= globalThis;
@@ -386,14 +397,17 @@ const main = async () => {
 
     // Is an FFI module specified?
     if (args.length > 2) {
-        // instantiate FFI module
-        var ffiInstance = instantiate(args[ffiArg], {});
-        // Make its exports available as imports under the 'ffi' module name
+        // Instantiate FFI module.
+        var ffiInstance = await WebAssembly.instantiate(await compile(args[ffiArg], false), {});
+        // Make its exports available as imports under the 'ffi' module name.
         importObject.ffi = ffiInstance.exports;
     }
 
     // Instantiate the Dart module, importing from the global scope.
-    var dartInstance = await dart2wasm.instantiate(Promise.resolve(compile(args[wasmArg])), Promise.resolve(importObject));
+    var dartInstance = await dart2wasm.instantiate(
+        compile(args[wasmArg], detectImportedStrings()),
+        Promise.resolve(importObject),
+    );
 
     // Call `main`. If tasks are placed into the event loop (by scheduling tasks
     // explicitly or awaiting Futures), these will automatically keep the script

pkg/dart2wasm/lib/js/runtime_blob.dart

@@ -113,22 +113,6 @@ const jsRuntimeBlobPart3 = r'''
         return wrapped;
     }
 
-    if (WebAssembly.String === undefined) {
-        WebAssembly.String = {
-            "charCodeAt": (s, i) => s.charCodeAt(i),
-            "compare": (s1, s2) => {
-                if (s1 < s2) return -1;
-                if (s1 > s2) return 1;
-                return 0;
-            },
-            "concat": (s1, s2) => s1 + s2,
-            "equals": (s1, s2) => s1 === s2,
-            "fromCharCode": (i) => String.fromCharCode(i),
-            "length": (s) => s.length,
-            "substring": (s, a, b) => s.substring(a, b),
-        };
-    }
-
     // Imports
     const dart2wasm = {
 ''';
@@ -150,9 +134,25 @@ const jsRuntimeBlobPart5 = r'''
         Array: Array,
         Reflect: Reflect,
     };
+
+    const jsStringPolyfill = {
+        "charCodeAt": (s, i) => s.charCodeAt(i),
+        "compare": (s1, s2) => {
+            if (s1 < s2) return -1;
+            if (s1 > s2) return 1;
+            return 0;
+        },
+        "concat": (s1, s2) => s1 + s2,
+        "equals": (s1, s2) => s1 === s2,
+        "fromCharCode": (i) => String.fromCharCode(i),
+        "length": (s) => s.length,
+        "substring": (s, a, b) => s.substring(a, b),
+    };
+
     dartInstance = await WebAssembly.instantiate(await modulePromise, {
         ...baseImports,
         ...(await importObjectPromise),
+        "wasm:js-string": jsStringPolyfill,
     });
 
     return dartInstance;

sdk/lib/_internal/wasm/lib/js_string.dart

@@ -81,7 +81,8 @@ final class JSStringImpl implements String {
   @override
   String operator +(String other) {
     if (other is JSStringImpl) {
-      return JSStringImpl(_jsConcat(toExternRef, other.toExternRef));
+      return JSStringImpl(
+          _jsStringConcatImport(toExternRef, other.toExternRef));
     }
 
     // TODO(joshualitt): Refactor `string_patch.dart` so we can directly
@@ -712,32 +713,51 @@ bool _jsIdentical(WasmExternRef? ref1, WasmExternRef? ref2) =>
     js.JS<bool>('Object.is', ref1, ref2);
 
 @pragma("wasm:prefer-inline")
-int _jsCharCodeAt(WasmExternRef? stringRef, int index) => js
-    .JS<WasmI32>(
-        'WebAssembly.String.charCodeAt', stringRef, WasmI32.fromInt(index))
-    .toIntUnsigned();
-
-WasmExternRef _jsConcat(WasmExternRef? s1, WasmExternRef? s2) =>
-    js.JS<WasmExternRef>('WebAssembly.String.concat', s1, s2);
+int _jsCharCodeAt(WasmExternRef? stringRef, int index) =>
+    _jsStringCharCodeAtImport(stringRef, WasmI32.fromInt(index))
+        .toIntUnsigned();
 
 @pragma("wasm:prefer-inline")
 WasmExternRef _jsSubstring(
         WasmExternRef? stringRef, int startIndex, int endIndex) =>
-    js.JS<WasmExternRef>('WebAssembly.String.substring', stringRef,
-        WasmI32.fromInt(startIndex), WasmI32.fromInt(endIndex));
+    _jsStringSubstringImport(
+        stringRef, WasmI32.fromInt(startIndex), WasmI32.fromInt(endIndex));
 
 @pragma("wasm:prefer-inline")
 int _jsLength(WasmExternRef? stringRef) =>
-    js.JS<WasmI32>('WebAssembly.String.length', stringRef).toIntUnsigned();
+    _jsStringLengthImport(stringRef).toIntUnsigned();
 
 @pragma("wasm:prefer-inline")
 bool _jsEquals(WasmExternRef? s1, WasmExternRef? s2) =>
-    js.JS<WasmI32>('WebAssembly.String.equals', s1, s2).toBool();
+    _jsStringEqualsImport(s1, s2).toBool();
 
 @pragma("wasm:prefer-inline")
 int _jsCompare(WasmExternRef? s1, WasmExternRef? s2) =>
-    js.JS<WasmI32>('WebAssembly.String.compare', s1, s2).toIntSigned();
+    _jsStringCompareImport(s1, s2).toIntSigned();
 
 @pragma("wasm:prefer-inline")
-WasmExternRef _jsFromCharCode(int charCode) => js.JS<WasmExternRef>(
-    'WebAssembly.String.fromCharCode', WasmI32.fromInt(charCode));
+WasmExternRef _jsFromCharCode(int charCode) =>
+    _jsStringFromCharCodeImport(WasmI32.fromInt(charCode));
+
+@pragma("wasm:import", "wasm:js-string.charCodeAt")
+external WasmI32 _jsStringCharCodeAtImport(WasmExternRef? s, WasmI32 index);
+
+@pragma("wasm:import", "wasm:js-string.compare")
+external WasmI32 _jsStringCompareImport(WasmExternRef? s1, WasmExternRef? s2);
+
+@pragma("wasm:import", "wasm:js-string.concat")
+external WasmExternRef _jsStringConcatImport(
+    WasmExternRef? s1, WasmExternRef? s2);
+
+@pragma("wasm:import", "wasm:js-string.equals")
+external WasmI32 _jsStringEqualsImport(WasmExternRef? s1, WasmExternRef? s2);
+
+@pragma("wasm:import", "wasm:js-string.fromCharCode")
+external WasmExternRef _jsStringFromCharCodeImport(WasmI32 c);
+
+@pragma("wasm:import", "wasm:js-string.length")
+external WasmI32 _jsStringLengthImport(WasmExternRef? s);
+
+@pragma("wasm:import", "wasm:js-string.substring")
+external WasmExternRef _jsStringSubstringImport(
+    WasmExternRef? s, WasmI32 startIndex, WasmI32 endIndex);