Parse subslice patterns

[tomjakubowski]

cc #1479

[tomjakubowski]

This adds a new SyntaxKind for "subslice patterns", to match the b.. in something like if let [a, b..] = foo {}. atom_pat() gets a new branch to look for these. By the way, the syntax for those is due to change: rust-lang/rust#62254

I'm not sure what to do with the text in crates/ra_syntax/tests/data/parser/inline/ok/0024_slice_pat.txt, which is causing the test failure. Should I just replace the contents with the debug dump for the new test with a subslice pattern? Or should I just put it into a new test?

[tomjakubowski]

cargo run --bin ra_cli parse < crates/ra_syntax/tests/data/parser/inline/ok/0024_slice_pat.rs > crates/ra_syntax/tests/data/parser/inline/ok/0024_slice_pat.txt

That wasn't too bad!

[matklad]

Should I just replace the contents with the debug dump for the new test with a subslice pattern?

There's also REWRITE constant in the tests which you can set to true to update them

[matklad]

Hm, I think this would allow x.. anywhere where patterns are allowed, and not only inside slices. I think we need to adjust slice_pat instead.

[tomjakubowski]

Ahh you're right of course. I inlined pat_list() to slice_pat() and made the adjustment there. Seeing as pat_list() now only had one caller, I inlined it there and deleted it.

[tomjakubowski]

This was a valuable learning exercise! I'll update the issue and take another crack at it.