Arrow function body indentation affected by its type length

[kalekseev]

Environment information

CLI:
  Version:                      1.6.3
  Color support:                true

Platform:
  CPU Architecture:             aarch64
  OS:                           macos

Environment:
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  TERM:                         "screen-256color"
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Biome Configuration:
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  Linter disabled:              true
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Formatter:
  Format with errors:           true
  Indent style:                 Space
  Indent size:                  0
  Indent width:                 2
  Line ending:                  Lf
  Line width:                   90
  Attribute position:           Auto
  Ignore:                       []
  Include:                      []

JavaScript Formatter:
  Enabled:                      false
  JSX quote style:              Double
  Quote properties:             AsNeeded
  Trailing comma:               Es5
  Semicolons:                   Always
  Arrow parentheses:            Always
  Bracket spacing:              false
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JSON Formatter:
  Enabled:                      true
  Indent style:                 unset
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  Indent size:                  unset
  Line ending:                  unset
  Line width:                   unset
  Trailing Commas:              unset

Workspace:
  Open Documents:               0

Configuration

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  "organizeImports": {
    "enabled": false
  },
  "linter": {
    "enabled": false
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  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 90,
    "formatWithErrors": true
  },
  "javascript": {
    "formatter": {
      "trailingComma": "es5",
      "quoteStyle": "single"
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Playground link

https://biomejs.dev/playground/?lineWidth=90&code=YwBvAG4AcwB0ACAAVgBhAGwAdQBlAE0AZQBuAHUARABpAHYAaQBkAGUAcgA6ACAAUgBlAGEAYwB0AC4ARgBDADwAewAgAHYAYQBsAHUAZQA6ACAAcwB0AHIAaQBuAGcAIAB9ACAAJgAgAE8AbQBpAHQAPABNAGUAbgB1AEQAaQB2AGkAZABlAHIAUAByAG8AcABzACwAIAAnAHMAdgBhAGwAdQBlACcAPgA%2BACAAPQAgACgAewAgAHYAYQBsAHUAZQAgAH0AKQAgAD0APgAgAHsACgAgACAAcgBlAHQAdQByAG4AIAA8AE8AcgBpAGcAaQBuAGEAbABNAGUAbgB1AEQAaQB2AGkAZABlAHIAIAAvAD4AOwAKAH0AOwAKAAoACgAKAGMAbwBuAHMAdAAgAFYAYQBsAHUAZQBNAGUAbgB1AEQAaQB2AGkAZABlAHIAMgA6ACAAUgBlAGEAYwB0AC4ARgBDADwAewAgAHYAYQBsAHUAZQA6ACAAcwB0AHIAaQBuAGcAIAB9ACAAJgAgAE8AbQBpAHQAPABNAGUAbgB1AEQAaQB2AGkAZABlAHIAUAByAG8AcABzACwAIAAnAHMAdgBhAGwAdQBlACcALAAgACcAYQBuAG8AdABoAGUAcgB2AGEAbAB1AGUAJwA%2BAD4AIAA9ACAAKAB7ACAAdgBhAGwAdQBlACAAfQApACAAPQA%2BACAAewAKACAAIAByAGUAdAB1AHIAbgAgADwATwByAGkAZwBpAG4AYQBsAE0AZQBuAHUARABpAHYAaQBkAGUAcgAgAC8APgA7AAoAfQA7AAoA

Code of Conduct

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[dyc3]

I'd like to give this a shot.

[dyc3]

I have a smaller repro here: https://biomejs.dev/playground/?code=YwBvAG4AcwB0ACAAVgBhAGwATQBlAG4AdQBEAGkAdgBpAGQAZQA6ACAAUgBlAGEAYwB0AEYARgBDADwATQBlAGQAZABkAGQAZABkAGQAZABkAE0AZQBuAHUARABpAHYAaQBkAGUAcgBQAHIAbwBwAHMATQBlAG4AdQBEAGkAdgBpAGQAZQByAFAAcgBvAHAAcwB6AHoAegA%2BAD0AKAB4ACkAIAA9AD4AIAA1ADsACgA%3D

[dyc3]

I've been combing over the code for a while now, and I think I understand what's going on. Mostly notes for myself:

The variable declaration group is higher up in the IR tree than the type annotation group. When the tree gets flattened into FormatElements, the variable declaration group gets evaluated first to see if it breaks (and since it's long enough, it breaks). Then the type annotation group gets evaluated, and its not long enough, so it doesn't break. This evaluation happens here:

biome/crates/biome_formatter/src/printer/mod.rs

Lines 184 to 188 in 01c440d

	// Measure to see if the group fits up on a single line. If that's the case,
	// print the group in "flat" mode, otherwise continue in expanded mode
	stack.push(TagKind::Group, args.with_print_mode(PrintMode::Flat));
	let fits = self.fits(queue, stack, indent_stack)?;
	stack.pop(TagKind::Group)?;

I think one way to fix this is to introduce some kind of "break priority" field to the Group struct, and then favor breaking type annotations, but I think that could introduce some complexity.

[ah-yu]

I think one way to fix this is to introduce some kind of "break priority" field to the Group struct, and then favor breaking type annotations, but I think that could introduce some complexity.

It seems that this approach assumes the current generated IR is accurate. Perhaps we could compare the IR generated by Biome and Prettier to identify differences between them and address these disparities to see if the issue is resolved.

[dyc3]

Ok yeah, I was looking at the IR before and it looked identical, but I'm looking at it again and it is definitely not. Biome is emitting an extra group around the left hand side of the assignment.