Add optional collection size indicator

[alexkunin]

This is my attempt to add requested functionality. Few notes:

1. Disabled by default, can be enabled by setting FX_SHOWSIZES environment variable to a truthy value(true, on, 1, yes, case does not matter).
2. Size indicator is formatted as /* 123 */ -- to avoid confusing with actual values (e.g. [ 123 ] could be read as array with single numeric element)
3. Theme has separate color for size indicator, currently in all themes it is the same color which was used for ...
4. For arrays, it replaces ... with size indicator.
5. For objects, it replaces first key and ... with size indicator (notation like {"name":/* 123 */ would be very confusing).

closes #278

[antonmedv]

Nice! But is it possible to display numbers outside brackets?

"foo": [...], // 123

[alexkunin]

Sure, done: counts are now in outside object/array.

One things I have noticed, previous iteration of my PR failed due to missing package slices. Which I had fixed by making sure the code works with go 1.20, per go.mod. But, actual error message looked like this:

Error: theme.go:8:2: package slices is not in GOROOT (/opt/hostedtoolcache/go/1.18.10/x64/src/slices)

So, tests seem to be executed with go 1.18, which also can be seen in .github/workflows/test.yml. Not sure if this is a big deal tho, just FYI.

[antonmedv]

Renamed to FX_SHOW_SIZE as it already once was: #138 (comment)

[antonmedv]

What about this style?

[antonmedv]

And what about showing size for expanded nodes as well?

[alexkunin]

I don't mind adding that, but honestly it rises questions:

1. Switching styles between collapsed and uncollapsed states might be confusing -- I mean, they're like totally different.
2. Having size next to collapsed node is totally fine. But what if huge node (hundreds? thousands?) is expanded:
   • should I add indicator at the start?
   • or at the end?
   • or both?
   • what about both start and end of the node are out of the view?
3. Previously if you select and copy fully expanded JSON, result was a valid JSON, but with this change it's not anymore.

What would be the next smallest change to implement to avoid breaking things too much and still add some vallue, in your opinion?

[antonmedv]

1. Lets just use grey style.
2. Only at first bracket. Not if size is 1.
3. Yank value will always copy correct JSON.

[alexkunin]

Oh, you did that already... I thought you were suggesting me doing it. Well done!