Don't use new WebAssembly.Function by default (#24581)

The js-types proposal has been, unfortunately, stuck for a couple of
years now, and is only available under a flag in certain browsers.

It makes sense to include it only under an explicit opt-in flag for now
to save a bit of code size.

Author: RReverser

site/source/docs/tools_reference/settings_reference.rst

@@ -3342,3 +3342,14 @@ or chrome.
 .. note:: This is an experimental setting
 
 Default value: false
+
+.. _wasm_js_types:
+
+WASM_JS_TYPES
+=============
+
+Experimental support for WebAssembly js-types proposal.
+It's currently only available under a flag in certain browsers,
+so we disable it by default to save on code size.
+
+Default value: false

src/lib/libaddfunction.js

@@ -17,7 +17,7 @@ addToLibrary({
       target.push((n % 128) | 128, n >> 7);
     }
   },
-
+#if WASM_JS_TYPES
   // Converts a signature like 'vii' into a description of the wasm types, like
   // { parameters: ['i32', 'i32'], results: [] }.
   $sigToWasmTypes: (sig) => {
@@ -48,6 +48,7 @@ addToLibrary({
     }
     return type;
   },
+#endif
   $generateFuncType__deps: ['$uleb128Encode'],
   $generateFuncType: (sig, target) => {
     var sigRet = sig.slice(0, 1);
@@ -85,7 +86,13 @@ addToLibrary({
   },
   // Wraps a JS function as a wasm function with a given signature.
 #if !WASM2JS
-  $convertJsFunctionToWasm__deps: ['$uleb128Encode', '$sigToWasmTypes', '$generateFuncType'],
+  $convertJsFunctionToWasm__deps: [
+    '$uleb128Encode',
+#if WASM_JS_TYPES
+    '$sigToWasmTypes',
+#endif
+    '$generateFuncType'
+  ],
 #endif
   $convertJsFunctionToWasm: (func, sig) => {
 #if WASM2JS
@@ -95,15 +102,15 @@ addToLibrary({
 #if ASSERTIONS && !WASM_BIGINT
     assert(!sig.includes('j'), 'i64 not permitted in function signatures when WASM_BIGINT is disabled');
 #endif
-
+#if WASM_JS_TYPES
     // If the type reflection proposal is available, use the new
     // "WebAssembly.Function" constructor.
     // Otherwise, construct a minimal wasm module importing the JS function and
     // re-exporting it.
     if (typeof WebAssembly.Function == "function") {
       return new WebAssembly.Function(sigToWasmTypes(sig), func);
     }
-
+#endif
     // The module is static, with the exception of the type section, which is
     // generated based on the signature passed in.
     var typeSectionBody = [
@@ -252,4 +259,3 @@ addToLibrary({
     freeTableIndexes.push(index);
   },
 });
-

src/lib/libasync.js

@@ -20,7 +20,7 @@ addToLibrary({
   },
 
 #if ASYNCIFY
-  $Asyncify__deps: ['$runAndAbortIfError', '$callUserCallback', '$sigToWasmTypes',
+  $Asyncify__deps: ['$runAndAbortIfError', '$callUserCallback',
 #if !MINIMAL_RUNTIME
     '$runtimeKeepalivePush', '$runtimeKeepalivePop',
 #endif

src/settings.js

@@ -2184,6 +2184,11 @@ var WASM_ESM_INTEGRATION = false;
 // [link]
 var JS_BASE64_API = false;
 
+// Experimental support for WebAssembly js-types proposal.
+// It's currently only available under a flag in certain browsers,
+// so we disable it by default to save on code size.
+var WASM_JS_TYPES = false;
+
 // For renamed settings the format is:
 // [OLD_NAME, NEW_NAME]
 // For removed settings (which now effectively have a fixed value and can no

test/other/codesize/test_codesize_hello_O0.gzsize

@@ -1 +1 @@
-8345
+8337

test/other/codesize/test_codesize_hello_O0.jssize

@@ -1 +1 @@
-22435
+22420

test/other/codesize/test_codesize_hello_dylink.gzsize

@@ -1 +1 @@
-11659
+11562

test/other/codesize/test_codesize_hello_dylink.jssize

@@ -1 +1 @@
-27545
+27310

test/other/codesize/test_codesize_minimal_O0.expected.js

@@ -926,7 +926,6 @@ Module['FS_createPreloadedFile'] = FS.createPreloadedFile;
   'ccall',
   'cwrap',
   'uleb128Encode',
-  'sigToWasmTypes',
   'generateFuncType',
   'convertJsFunctionToWasm',
   'getEmptyTableSlot',

test/other/codesize/test_codesize_minimal_O0.gzsize

@@ -1 +1 @@
-6639
+6632

test/other/codesize/test_codesize_minimal_O0.jssize

@@ -1 +1 @@
-17698
+17683

test/other/test_unoptimized_code_size.js.size

@@ -1 +1 @@
-54182
+54162

test/other/test_unoptimized_code_size_strict.js.size

@@ -1 +1 @@
-52232
+52212

tools/link.py

@@ -821,6 +821,9 @@ def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
     if settings.ABORT_ON_WASM_EXCEPTIONS:
       exit_with_error('WASM_ESM_INTEGRATION is not compatible with ABORT_ON_WASM_EXCEPTIONS')
 
+  if settings.WASM_JS_TYPES:
+    diagnostics.warning('experimental', '-sWASM_JS_TYPES is only supported under a flag in certain browsers')
+
   if settings.MODULARIZE and settings.MODULARIZE not in [1, 'instance']:
     exit_with_error(f'Invalid setting "{settings.MODULARIZE}" for MODULARIZE.')