Bug 197472 – Pyodide WASM bundle fetched but won't load ("Unhandled promise rejection"), works on FF / Chrome

• Status: RESOLVED
• Resolution: FIXED
• Component: WebAssembly

[Joseph D. Long]

Using Safari Version 12.1 (14607.1.40.1.4) and the latest Safari Technology Preview (Release 80 (Safari 12.2, WebKit 14608.1.16)) on macOS 10.14.4, I am unable to run pyodide examples (though other iodide examples work). Pyodide fetches a WASM archive with Python + scientific packages cross-compiled to WebAssembly, and uses them to execute Python in the browser. For context, see https://hacks.mozilla.org/2019/04/pyodide-bringing-the-scientific-python-stack-to-the-browser/ .

The only error that appears in the (devtools) console when I try to run a %% py block is

[Error] Unhandled Promise Rejection: undefined
	(anonymous function)
	rejectPromise
	promiseReactionJob

I carved out a subset of one of the Pyodide examples that reproduces this behavior here: https://alpha.iodide.io/notebooks/2154/ (Click in text field after '%% py' and "Shift-Enter" to execute.)

Corresponding Pyodide bug: https://github.com/iodide-project/pyodide/issues/402

It's entirely possible this is a Pyodide bug that is being obscured by the default behavior in Firefox and Chrome, but I cannot find anywhere in the Safari Dev Tools that will expose what exactly is happening. Another pair of eyes on this would be very helpful! Thanks in advance.

[Joseph D. Long]

Also present in today's Safari Technology Preview Release 81.

[Joseph D. Long]

The underlying issue was a call to WebAssembly.compileStreaming, which is not (yet) available on Safari. I'm not sure why this was not visible from the traceback, but a debug / non-minified build showed the culprit. Closing.

[Radar WebKit Bug Importer]

<rdar://problem/50448468>