Support subslice patterns

[Undin]

Subslice patterns will be stabilized in 1.42. It would be great to support them in the plugin.
Some technical details can be found in rust-lang/rust#67712

• syntax Better support of range and rest patterns #4778
• type inference
• annotations and inspections
  • experimental feature check
  • exhaustiveness

[fujiapple852]

I see from the above that type inference is not yet available for subslice patterns and therefore presumably I shouldn't expect the type of xs to be inferred correctly at the moment?

fn foo() {
    fn bar(_: &[&str]) {}
    match vec![""].as_slice() {
        [] => {},
        [_, xs @ ..] => bar(xs)
    }
}

Currently this gives a type inference error in the IDE:

mismatched types [E0308] expected `&[&str]`, found `&&str`

If not let me know and I'll raise a bug.

[Undin]

@fujiapple852 type inference is implemented in #5226
You can try it in tomorrow nightly build. See instruction how to install nightly plugin version