[dart2wasm] Move Wasm compilation functions into generated runtime blob

To be able to control how dart2wasm-generated modules are compiled, add
a `WebAssembly.compile` and `WebAssmebly.compileStreaming` wrapper to
the generated runtime blob.

These wrappers do js-string built-in detection and enable the built-in
when it's available.

Once the SDK is rolled into engine we will update the engine dart2wasm
module loader to use `compileStreaming` from the runtime blob, in
flutter/engine#51488.

This will allow enabling the built-in without duplicating the feature
detection and compilation code in the engine.

Change-Id: Icb939f16a2b0ae1d348ec5a814371e9ffde4fd68
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381581
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Ömer Ağacan <[email protected]>

Author: osa1

pkg/dart2wasm/bin/run_wasm.js

@@ -370,18 +370,7 @@ if (argsSplit != -1) {
 const main = async () => {
     const dart2wasm = await import(args[jsRuntimeArg]);
 
-    /// 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) {
+    function compile(filename) {
         // Create a Wasm module from the binary Wasm file.
         var bytes;
         if (isJSC) {
@@ -391,10 +380,7 @@ const main = async () => {
         } else {
           bytes = readRelativeToScript(filename, "binary");
         }
-        return WebAssembly.compile(
-            bytes,
-            withJsStringBuiltins ? {builtins: ['js-string']} : {}
-        );
+        return dart2wasm.compile(bytes);
     }
 
     globalThis.window ??= globalThis;
@@ -411,7 +397,7 @@ const main = async () => {
 
     // Instantiate the Dart module, importing from the global scope.
     var dartInstance = await dart2wasm.instantiate(
-        compile(args[wasmArg], detectImportedStrings()),
+        compile(args[wasmArg]),
         Promise.resolve(importObject),
     );
 

pkg/dart2wasm/lib/js/runtime_blob.dart

@@ -3,6 +3,42 @@
 // BSD-style license that can be found in the LICENSE file.
 
 const jsRuntimeBlobPart1 = r'''
+// Returns whether the `js-string` built-in is supported.
+function detectJsStringBuiltins() {
+    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']});
+}
+
+// Compile a dart2wasm-generated Wasm module using
+// `WebAssembly.compileStreaming`, with the flags needed by dart2wasm. `source`
+// needs to have a type expected by `WebAssembly.compileStreaming`.
+//
+// Pass the output of this to `instantiate` below to instantiate the compiled
+// module.
+export const compileStreaming = (source) => {
+    return WebAssembly.compileStreaming(
+        source,
+        detectJsStringBuiltins() ? {builtins: ['js-string']} : {}
+    );
+}
+
+// Compile a dart2wasm-generated Wasm module using `WebAssembly.compile`, with
+// the flags needed by dart2wasm. `source` needs to have a type expected by
+// `WebAssembly.compileStreaming`.
+//
+// Pass the output of this to `instantiate` below to instantiate the compiled
+// module.
+export const compile = (bytes) => {
+    return WebAssembly.compile(
+        bytes,
+        detectJsStringBuiltins() ? {builtins: ['js-string']} : {}
+    );
+}
 
 // `modulePromise` is a promise to the `WebAssembly.module` object to be
 //   instantiated.

pkg/test_runner/lib/src/browser.dart

@@ -328,11 +328,11 @@ String dart2wasmHtml(String title, String wasmPath, String mjsPath) {
           src="/root_dart/pkg/test_runner/lib/src/test_controller.js">
   </script>
   <script type="module">
-  const dartModulePromise = WebAssembly.compileStreaming(fetch('$wasmPath'));
-  const imports = {};
   let dart2wasm_runtime = await import('$mjsPath');
+  const dartModulePromise =
+      dart2wasm_runtime.compileStreaming(fetch('$wasmPath'));
   let moduleInstance =
-      await dart2wasm_runtime.instantiate(dartModulePromise, imports);
+      await dart2wasm_runtime.instantiate(dartModulePromise, {});
 
   dartMainRunner(() => {
     dart2wasm_runtime.invoke(moduleInstance);