Tracking issue for highlighted diffs

[dtolnay]

Requires opt-in for now (cargo test --features trybuild/diff).

Currently unix-only. We will need to look into how to get highlighted background color reliably on Windows terminals, and ideally implement support for it in https://github.com/BurntSushi/termcolor.

Our diff algorithm is backed by https://github.com/dtolnay/dissimilar which is intended to produce human readable diffs with less noise than raw Myers' algorithm.

The intended output looks like:

[CreepySkeleton]

@dtolnay Would it be possible to introduce TRYBUILD_DIFF=auto/always/never environment variable? Sometimes (quite often) the diff is not shown but I need it.

[dtolnay]

Can you give an example output when you need a diff but it is not shown? There are heuristics that determine when a diff is worth showing and we can adjust those.

[CreepySkeleton]

Expected

error: parse must have exactly one argument
  --> $DIR/parse_not_zero_args.rs:14:17
   |
14 |     #[structopt(parse(from_str, from_str))]

Actual

error: `parse` must have exactly one argument
  --> $DIR/parse_not_zero_args.rs:14:17
   |
14 |     #[structopt(parse(from_str, from_str))]

[dtolnay]

Looks fine to me.

[CreepySkeleton]

Doesn't work in Git Bash for windows

trybuild 1.0.21

[dtolnay]

Yep, it says at the top of the issue this is currently unix-only. Termcolor would need a highlighting implementation for windows before I would try to make it work there.

[pksunkara]

IIRC termcolor has support for windows and we used that for clap. Not sure what the issue here is.