"introduce match" action

[killercup]

Similar to "introduce variable", an "introduce match" action would replace the x under cursor here

fn maybe() -> Option<i32> { Some(42) }

fn foo() {
    let x = maybe();
    x<|>
}

with this:

    match x {
        _ => (),
    }

Assuming knowledge of the type of x, we could later on add special cases, e.g. for booleans (use if) or enums with two variants (use if let).

This is similar to #525 but maybe a bit more user-discoverable ;) Feel free to close this issue if you feel like #525 is a better approach.

[matklad]

Good idea, I think we need both this and #525 !

[flodiebold]

Also, with a code action the user can select the expression to match on -- with a completion we have to guess it.

[zacps]

Similarly it'd be nice to be able to convert an if let to a match.

[matklad]

@zacps this already works for iflets with else: https://github.com/rust-analyzer/rust-analyzer/blob/master/crates/ra_assists/src/handlers/replace_if_let_with_match.rs

Should be straightforward to extend to plain iflets

[matklad]

Hm, now that I think about it, just using prefix/postfix completions for this seems to be a better idea in terms of cost/benefit.