Improve struct fields' completion

[SomeoneToIgnore]

Environment

• IntelliJ Rust plugin version: 0.2.106.2134-193
• Rust toolchain version: 1.37.0 (eae3437df 2019-08-13) x86_64-apple-darwin
• IDE name and version: CLion 2019.3 EAP (CL-193.3519.24)
• Operating system: macOS 10.14.6

Problem description

• [x] 1. Odd options for field completion:

pub struct MouseButtonDown {
    timestamp: u32,
    window_id: u32,
    which: u32,
    mouse_btn: MouseButton,
    clicks: u8,
    x: i32,
    y: i32
}

fn main() {
    let test = MouseButtonDown {/*caret*/}
}

Expected: only field names are available for completion, maybe a bunch of local variables. Actual: let and return are present:

• [ ] 2. Field completion can be improved.

Same example as in 1., try to complete any of the fields.

Expected: a semicolon is added if no matching local variables are in scope:

fn main() {
    let test = MouseButtonDown {timestamp: /*caret*/}
}

Actual: I have to add it myself

fn main() {
    let test = MouseButtonDown {timestamp/*caret*/}
}

• [x] 3. No proper completion when destructuring the variable:

pub struct MouseButtonDown {
    timestamp: u32,
    window_id: u32,
    which: u32,
    mouse_btn: MouseButton,
    clicks: u8,
    x: i32,
    y: i32,
}

fn get_event() -> MouseButtonDown {
    unimplemented!()
}

fn main() {
    match get_event() {
        MouseButtonDown { /*caret*/ }
    }
}

Expected: only struct field names and .. are available Actual:

[Undin]

Reopened because we reverted #5659

[Kobzol]

@SomeoneToIgnore I implemented 2) in https://github.com/intellij-rust/intellij-rust/pull/5659, but it maybe it's not such a good idea (https://github.com/intellij-rust/intellij-rust/issues/5875#issuecomment-669428733). Do you still want that functionality or can this issue be closed?

[SomeoneToIgnore]

Oh, don't mind me if you think there are better ways to do something, so go ahead and close it. Thanks for your contriburions!

[Kobzol]

Ok :) I'll close it, since it's unclear if inserting : is always what the user wants, it's a bit unpredictable.