Clippy test warnings

[danielvallance]

This PR enables clippy::assertions_on_result_states, because asserting that a Result is_ok(), or is_err() causes the unit test failure messages to be quite unhelpful (as described in issue 337 #337).

It also addresses a couple of other clippy warnings.

[XanClic]

Looks good, just some nit picks, mainly:

• If we’re asserting a value in an address that’s been part of the previous code, it should have the same form as previously, i.e. assert on usize::MAX instead of 18446744073709551615 and on 0x600 instead of 1536 if the value was previously given as 0x600. Especially so in examples that end up in documentation.
• I’m not sure about dropping assert!(foo.is_ok()) from documentation examples just because it’s immediately followed by foo.unwrap(). I’m all for replacing .is_ok() by .unwrap() in tests, but in examples, .is_ok() adds an explicit “We’re not just unwrapping for simplicity’s sake, but this example is actually supposed to show that this operation will return Ok(_)”.

[XanClic]

Not up to this PR but a general question to everyone: Why does this (and the ones below) report 101? That address is not part of the requested subslice, instead it should be 100 in my understanding…

I think compute_end_offset() should use addr: cmp::max(self.len(), base) instead of addr: mem_end, and VolatileSlice::offset() should use addr: self.addr + self.size (or something like that) instead of addr: new_addr.

(As for this PR, this is a nice example why using this assertion style is better :))

[roypat]

iirc there are some subtleties where we can request a slice of length 0 one byte past the end of a volatile slice, and it'll work (e.g. if length is 80, then doing subslice(80, 0) will give you an empty slice), and I suspect this is an artifact of that. There's some more oddities like this, such as some read/write impls allowing you to always read/write length-0 slices into guest memory even if the address you pass in is complete bollocks :/

[danielvallance]

Hi @XanClic thank you for taking the time to review this, I have addressed your comments :)

[XanClic]

Thanks! :)

[roypat]

Nice work, thank you so much for tackling this!