[diffs] add folding support

[ije]

• Add folding option for File and FileDiff options. (Default is false)
• Works in edit mode
• Support both split and unified diffs layouts
• Support A11y

Usage

new File({
  folding: true,
});

new FileDiff({
  folding: true,
});

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[ije]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid sending folded bodies through render windows

When a viewport contains both the folded header and the first visible line after a large collapsed body (for example folding lines 1–19990), startingLine can be the header while finalLine is after the fold, so this returns a render window spanning the entire hidden body. FileRenderer.renderFile forwards startingLine/totalLines into windowed plain rendering before it skips foldRanges, which means large folded regions are still sliced/joined/tokenized even though only a few visible rows are needed; please avoid passing hidden spans to the renderer or make that path skip folded bodies.

Useful? React with 👍 / 👎.

[tomerzcod7]

Hey guys, thanks for working on this - we use your library extensively and this is one feature we've been needing.
Please let me know if this is not the place for a comment like this.

We have a common use case, where we use the React File component as a read-only viewer, particularly for large, pretty-printed JSON files. We’d love to use the new nested folding controls there without enabling edit mode.
Any chances you would be open to support folding for read-only File component as well? maybe via the FileOptions?
Alternatively, is there an intended way to attach the experimental Editor for folding while preventing content edits?

We would love to adopt an experimental version and would be happy to test it and provide feedback.

[ije]

Any chances you would be open to support folding for read-only File component as well?

this makes sense to me, will support!