Allow fold when function declaration is in multiple lines Dart

Type: Bug

I’m filing this issue in the Dart extension because I have not been able to reproduce this exact behavior in languages like Python or C, even with the same parameter formatting. It’s relevant because this type of formatting is provided by dartfmt and makes the fold feature useless.

Environment: OS: Windows Version: 1.73.1 Reproducibility rate: 100%

Steps to reproduce:

1. Create a Dart function such as: Future<void> function(String param1, String param2, String param3) async { // content // content // content }
2. Try to fold the function

Expected Result: The function folds and all the content and parameters are hidden.

Actual Result: Only the function parameters are folded and the content stays visible.

Extension version: 3.52.1 VS Code version: Code 1.73.1 (6261075646f055b99068d3688932416f2346dd3b, 2022-11-09T04:27:29.066Z) OS version: Windows_NT x64 10.0.22000 Modes: Sandboxed: No

System Info

Item	Value
CPUs	11th Gen Intel® Core™ i7-11850H @ 2.50GHz (16 x 2496)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: disabled_off
Load (avg)	undefined
Memory (System)	31.67GB (16.43GB free)
Process Argv	–crash-reporter-id 923bf38f-184f-4b44-8523-aba43b319e5f
Screen Reader	no
VM	0%

A/B Experiments

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[DanTup]

With https://github.com/dart-lang/sdk/commit/35d3015ed5006b0a66ce9bbf742c7fe28453735f, whole function declarations (instead of just bodies) can be folded. There are also some other minor tweaks to ranges to improve handling of parameter lists when they start on the same line as the declaration (so they can still be folded).

This change is in the Dart language server so the fixes will show up with a future SDK update (rather than a Dart VS Code extension update).

[DanTup]

TypeScript (which I generally use as a template because it’s maintained by the VS Code team) does fold the whole declaration, but doesn’t allow folding of parameter lists:

https://user-images.githubusercontent.com/1078012/202503853-3d5106f5-e141-499d-b3b9-3560c7b0aa87.mp4

I think there may be some value in folding parameter lists (I suspect on average Flutter code has longer parameter lists and/or more likely has them split over a larger number of lines) but I’m not against removing them if they feel redundant.

Review on the way shortly.