feat: add support for folding ranges for chained expressions

[roife]

fix #19620.

[roife]

I'm interested in the support for collapsed_text, so I will convert this to a draft PR for now.

[roife]

I have finished a prototype:

If we fold the line let navs...

---

[roife]

Currently, this feature only works on nvim, as it is the only editor that supports collapsed_text.

One of the nvim maintainers mentioned that syntax highlighting will be applied to collapsed text in the future, which enhancing its appearance.

[Veykril]

I don't think this needs a config. This feels like something the client can expose as a config itself (as it is free to discard the collapsedText field instead of using it)

[roife]

as it is free to discard the collapsedText field instead of using it

While it does not impact functionality, it may decrease both the computational load and the size of responses.

[roife]

I refactored the code in the new commit based on the previous review and simplified the implementation of build_fold.

[Young-Flash]

any update on this?

[Copilot]

Pull request overview

This PR adds support for folding ranges for chained expressions in rust-analyzer, addressing issue #19620. The implementation introduces collapsed text functionality that provides preview text when folding multi-line statements and tail expressions.

Key changes:

• Extended FoldKind enum with Stmt and TailExpr variants to support folding of statements and tail expressions
• Added collapsed_text field to Fold struct to provide preview text for folded regions
• Implemented collapse_expr function to generate preview text for chain method calls and other expressions
• Added client capability detection for folding_range.collapsed_text support

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/ide/src/folding_ranges.rs	Core implementation of statement/tail expression folding and collapsed text generation
crates/ide/src/lib.rs	Updated folding_ranges API signature to accept collapsed_text parameter
crates/ide/src/static_index.rs	Updated call to folding_ranges with new parameter
crates/rust-analyzer/src/handlers/request.rs	Added client capability check and passes flag to folding ranges computation
crates/rust-analyzer/src/lsp/capabilities.rs	Added method to detect client support for collapsed text in folding ranges
crates/rust-analyzer/src/lsp/to_proto.rs	Updated LSP protocol conversion to include collapsed text with proper indentation handling

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[roife]

any update on this?

Sorry, I've been busy finishing my master's thesis looking for a job recently.

I have resolved the conflicts. @Veykril Do you have any suggestions?