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Use new URL(..., import.meta.url) pattern in minimal runtime if EXPORT_ES6 is enabled #26039

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Use new URL(..., import.meta.url) pattern in minimal runtime if EXPORT_ES6 is enabled #26039

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13 changes: 11 additions & 2 deletions src/postamble_minimal.js
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Original file line number Diff line number Diff line change
Expand Up @@ -182,6 +182,15 @@ var imports = {
};

#if MINIMAL_RUNTIME_STREAMING_WASM_INSTANTIATION
#if EXPORT_ES6 && !ENVIRONMENT_MAY_BE_AUDIO_WORKLET
var moduleUrl = new URL('{{{ TARGET_BASENAME }}}.wasm', import.meta.url);
#elif !EXPORT_ES6 || AUDIO_WORKLET
var moduleUrl = '{{{ TARGET_BASENAME }}}.wasm';
#else
var moduleUrl = ENVIRONMENT_IS_AUDIO_WORKLET ?
'{{{ TARGET_BASENAME }}}.wasm' :
new URL('{{{ TARGET_BASENAME }}}.wasm', import.meta.url);
#endif
// https://caniuse.com/#feat=wasm and https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiateStreaming
#if MIN_SAFARI_VERSION < 150000 || ENVIRONMENT_MAY_BE_NODE
#if ASSERTIONS && !WASM2JS
Expand All @@ -197,13 +206,13 @@ instantiatePromise =
// Node's fetch API cannot be used for local files, so we cannot use instantiateStreaming
&& !ENVIRONMENT_IS_NODE
#endif
? WebAssembly.instantiateStreaming(fetch('{{{ TARGET_BASENAME }}}.wasm'), imports)
? WebAssembly.instantiateStreaming(fetch(moduleUrl), imports)
: WebAssembly.instantiate(Module['wasm'], imports)).then((output) => {
#else
#if AUDIO_WORKLET
instantiatePromise =
#endif
WebAssembly.instantiateStreaming(fetch('{{{ TARGET_BASENAME }}}.wasm'), imports).then((output) => {
WebAssembly.instantiateStreaming(fetch(moduleUrl), imports).then((output) => {
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@sbc100 sbc100 Jan 9, 2026

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You could use the same trick we use in src/lib/libpthread.js to avoid creating a new variable here maybe?

i.e. do {{{ moduleUrl }}} here and then define moduleUrl inside a {{{ }}} block above?

#endif

#else // Non-streaming instantiation
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12 changes: 12 additions & 0 deletions test/test_other.py
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Expand Up @@ -1702,6 +1702,18 @@ def test_minimal_runtime_errors(self):
expected = 'emcc: error: MINIMAL_RUNTIME is not compatible with --preload-file'
self.assert_fail([EMCC, test_file('hello_world.c'), '-sMINIMAL_RUNTIME', '--preload-file', 'foo'], expected)

def test_minimal_runtime_esm_streaming_instantiation(self):
self.run_process([EMCC, '-o', 'test.mjs',
'-sMINIMAL_RUNTIME',
'-sMINIMAL_RUNTIME_STREAMING_WASM_INSTANTIATION',
'-sEXPORT_ES6',
'-sENVIRONMENT=web',
test_file('hello_world.c')])

src = read_file('test.mjs')
# Verify that the generated code uses import.meta.url for the wasm URL
self.assertContained("new URL('test.wasm', import.meta.url)", src)
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@sbc100 sbc100 Jan 9, 2026

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We have test_vite in test_browser.py what should be able to not only test that this string exists but that it works in the vite bundler.

IIUC we could add a variant of that test that uses -sMINIMAL_RUNTIME -sMINIMAL_RUNTIME_STREAMING_WASM_INSTANTIATION ?


def test_export_all_and_exported_functions(self):
# EXPORT_ALL should not export library functions by default.
# This means that to export library function you also need to explicitly
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