More powerful folding ranges API

[matklad]

When VS Code folds the range, it just completely hides its contents:

When IntelliJ folds the range, it shows a certain replacement string instead:

The latter behavior is more flexible, and it would be cool if the protocol supported it. It allows for the following features:

• folding a subrange in the string, which allows to hide boilerplate (see this post for example)

• folded blocks take one line instead of two:

• showing some important info from the fold, without making it more verbose:

To implement these features, we need to add two things to the protocol:

• a replacementText?: string field to FoldingRange (this covers bullet points 1 & 2)
• add a group?: number field to FoldingRange, such that all ranges in the group are folded-unfolded in lockstep. This covers use case 3, where { and } are separate folding ranges, linked into one group

However, I assume that the bulk of work here needs to happen on the editor's side as it seems like VS Code doesn't support such replacements yet.

[dbaeumer]

@aeschli can you please have a look.

[aeschli]

replacementText makes sense. VSCode always shows ... and with your suggestion with could be made specific.
Not sure how group?: number is related to your screenshots above. That proposal sounds like FoldingRange.kind that we already have. What's the difference?

[matklad]

@aeschli group and kind are completely different, basically. Let me give a better example:

unfolded:

folded:

See how the folded body is displayed in three pieces:

• grayed-out {
• syntax-highlighted 92 + 2
• grayed-out }

This happens because there are actually two folding regions in the picture: from { to 92:

"{\n        "

and from 2 to }:

"\n    }"

The replacement text for the first region is {, the replacement text for the second region is }, and they have the same group. So, when the user folds either of the regions, they are both folded, and the single-line unfolded body is shown on the same line, with syntax highlighting, completion and all.

Note that this group feature is a strict addition on top of replacementText, replacementText would be useful even without group.

[aeschli]

ok I see.

[ris58h]

I'm not sure about group but replacementText definitely would be useful.
Could we split the issue into two?

[Young-Flash]

IntelliJ also provide the upward folding at the end of a folding range, it's convenient when user go thourgh a very long folding range, user can fold at the end instead of go back to the begin to fold it. can we provide it?

[matklad]

@Young-Flash I believe the current LSP request already provides all the necessary information to implement this UI. It’s up to the client (the editor) to draw (or not draw) visual indicators for both ends of the fold

[Young-Flash]

@Young-Flash I believe the current LSP request already provides all the necessary information to implement this UI. It’s up to the client (the editor) to draw (or not draw) visual indicators for both ends of the fold

thanks, so it's much more a vscode related issue.