fix ABI for raw pointers

[jrvidal]

👋 Hello from Stackblitz

We've noticed very buggy behavior when our Rust code requires a sizable amount of memory (above 2 GiB!). I've traced it back to __wbindgen_malloc returning negative pointers (!!), which screams "i32 overflow" 😬

From what I can gather, changing the WasmDescribe impl. for raw pointers (so they follow u32 ABI conventions instead of i32's) should fix it. I've added a references test to wasm-bindgen-cli, not sure how appropriate/useful is.

[daxpedda]

Yeah, this definitely looks like a bug to me:

wasm-bindgen/src/convert/impls.rs

Lines 208 to 242 in 46f52e9

	impl<T> IntoWasmAbi for *const T {
	type Abi = u32;
	#[inline]
	fn into_abi(self) -> u32 {
	self as u32
	}
	}
	impl<T> FromWasmAbi for *const T {
	type Abi = u32;
	#[inline]
	unsafe fn from_abi(js: u32) -> *const T {
	js as *const T
	}
	}
	impl<T> IntoWasmAbi for *mut T {
	type Abi = u32;
	#[inline]
	fn into_abi(self) -> u32 {
	self as u32
	}
	}
	impl<T> FromWasmAbi for *mut T {
	type Abi = u32;
	#[inline]
	unsafe fn from_abi(js: u32) -> *mut T {
	js as *mut T
	}
	}

@Liamolucko would you mind confirming this?

[Liamolucko]

Yep, I agree this is a bug. Thanks!

[d3lm]

Awesome! Thanks so much for this quick turn around and for merging this so quickly 🙌 Is there a chance we can get this released?

[daxpedda]

See #3530.