x/pkgsite/internal/fetch/dochtml/internal/render: leave a sample of values when trimming large string literals and composite literals

[pjebs]

In godoc.org: https://godoc.org/github.com/rocketlaunchr/google-search (for example),

If you have a map package-level variable with many many predefined values, it doesn't display any of them:

var GoogleDomains = map[string]string{ /* 198 elements not displayed */

}

It would be more useful if displayed some values to give an idea of the kind of values stored:

var GoogleDomains = map[string]string{
	"us":  "https://www.google.com/search?q=",
	"ac":  "https://www.google.ac/search?q=",
	"ad":  "https://www.google.ad/search?q=",
	... /* 195 elements not displayed */

[dmitshur]

Thanks for this feature request. I think this is a good idea to consider.

We're currently prioritizing feature development in the new x/pkgsite codebase per https://blog.golang.org/pkg.go.dev-2020 and issues like #37819 and #39144 (/cc @julieqiu). This is likely better suited as an issue for pkg.go.dev. Is that okay with you? (Otherwise, the issue tracker for godoc.org specifically is at https://github.com/golang/gddo/issues.)

[pjebs]

Anything's fine

[dmitshur]

The relevant code is in declVisitor.

Right now it replaces the entire thing that's too big, leaving just a comment. It can instead leave the first N elements/bytes and trim the rest, as long as it's viable to do so in a way that doesn't create misleading documentation.

It should be balanced with leaving too much that packages start hitting the maximum documentation size limit and not being displayed at all.

/cc @julieqiu @shaqque

[shaqque]

Related #38699