Fix bug with Handle::get_mut not allowing non-mutable access to the database

[obsgolem]

Resolves #546

[netlify]

✅ Deploy Preview for salsa-rs canceled.

Name	Link
🔨 Latest commit	e1c99c3
🔍 Latest deploy log	https://app.netlify.com/sites/salsa-rs/deploys/66b1f3be3b2c0f000899065e

[nikomatsakis]

Hmm, this is probably still relevant-- can you rebase this atop master? The handle code has gone away but you should see equivalent code in storage.rs

Also, can you add a test?

Thanks! 💜

[codspeed-hq]

CodSpeed Performance Report

Merging #548 will not alter performance

_{Comparing obsgolem:fix_handle_flag_bug (e1c99c3) with master (4c8e52a)}

Summary

✅ 1 untouched benchmarks

[MichaReiser]

I merged in the latest changes. We only need to add some tests

[MichaReiser]

I don't think this PR is still needed now that Handle has been removed because the only call-site of cancel_others is inside zalza_mut which always bumps the revision.

salsa/src/storage.rs

Lines 99 to 108 in 5d3b756

	fn zalsa_mut(&mut self) -> &mut Zalsa {
	self.storage().cancel_others(self);
	// The ref count on the `Arc` should now be 1
	let storage = self.storage_mut();
	let arc_zalsa_mut = storage.zalsa_impl.as_mut().unwrap();
	let zalsa_mut = Arc::get_mut(arc_zalsa_mut).unwrap();
	zalsa_mut.new_revision();
	zalsa_mut
	}

[nikomatsakis]

Ah, ok, I'll close it. It may be relevant if we add some way to explicitly cancel things. Thanks @obsgolem !