Bad sliders when adding nested expression in Rust

[Wilfred]

See 97b9a13d15f413398d0aa75ae0241658d4d9d1f5, options.rs 2/5. This might be another issue with skip unchanged logic shrinking too much.

[Wilfred]

Minimal repro (requires DFT_DBG_KEEP_UNCHANGED=t)

fn app() {
    x
        .arg(
            color
        )
}

After:

fn app() {
    x
        .arg(
            display
        )
        .arg(
            color
        )
}

[Wilfred]

After skipping unchanged, we're just comparing x with x.arg(display), which does the right thing.

[Wilfred]

Smaller repro:

Before:

x.arg(color)

After

x.arg().arg(color)

[Wilfred]

Clojure equivalent

; old
((.arg x) color)

; new
((.arg ((.arg x)) color)

[Wilfred]

Interestingly, penalising code for preferring contiguous items seems to improve results both in this file, and in typing_before.rs and load_before.rs.

[Wilfred]

typing_before.ml is improved, but load_before.js is worse. It's now preferring , over the string literals, which isn't ideal. Score should probably reflect atom length.