Jest: Collapse big diffs by default

[cpojer]

Both for snapshots and regular diffs in other matchers, the diffs often get unwieldy and huge. Let's find a good heuristic to collapse unimportant info by default and add an -e (--expand) flag to print the full diff. It should be intentionally different from --verbose.

Proposed heuristic:

• Always print small diffs, collapse unimportant diffs over N lines automatically
• Always print small diffs, collapse unimportant changes based on the ratio between changed/unchanged lines. If there is a high ratio of changed lines, show all changes.
• ...?

[aaronabramov]

a couple of thoughts:

• it's important to always print full diffs when running in CI mode.
• if we implement interactive snapshot updates, we can always show small diffs and then give an option to expand (press 'e' to expand snapshot diffs)

[Spy-Seth]

if we implement interactive snapshot updates, we can always show small diffs and then give an option to expand (press 'e' to expand snapshot diffs)

👍

If use with in watch mode --watch it could led to an interactive mode close of git stash --patch. It will allow the developer to browse interactively each change and validate each one separately. On each diff the developer could chose between: show next/previous diff, expand, update snapshot, ignore.

[thymikee]

@cpojer I wonder if something like this would suffice?

[cpojer]

@thymikee yeah that looks great! Why @@? Is that what other diff tools do?

[thymikee]

Yup, this is what my git diff tool output looks like, but it shows line number near the change.

Since snapshots are not showing any information about line number, I thought counting the trimmed lines would be just nice to have.

[cpojer]

Yeah I think this is nice! Are you going to send us a PR? :)

[cpojer]

I think we should keep 4 lines of context at least.

[thymikee]

Sure, done!

[cpojer]

We'll continue the conversation in the PR.