Weak references fails to automatic garbage collect

[yisibl]

Summary

wasm-bindgen 2.9.1 has --weak-refs turned on by default, but I recompiled resvg-js to wasm to test it in Node.js and it still shows a constant increase in memory usage.

  const pngData = resvg.render()
  const pngBuffer = pngData.asPng()
  // pngData.free() // I had to add `.free()` here to memory leak.

The documentation for wasm-bindgen says:

Without weak references your JS integration may be susceptible to memory leaks in Rust, for example:
You could forget to call .free() on a JS object, leaving the Rust memory allocated.

Please help me see what went wrong.

See https://github.com/yisibl/repro-resvg-wasm-memory-leak

[Liamolucko]

This is a bug; somebody already noticed this and wrote a fix for it in #3743, but it never got finished.

We probably should've waited for this to be fixed before enabling weak references by default, but I'd forgotten about it... oops.

[yisibl]

@Liamolucko There is another related issue #3854

[mizdra]

The cause of this memory leak is as described at thx/resvg-js#318 (comment). It contains both #3854 and #3917 issues.

I think we can close this issue in favor of the two issues.

What do you think? @yisibl

[daxpedda]

Closing in favor of #3854.