feat(format/yaml): flow mappings

[dyc3]

Summary

This PR formats yaml flow mappings.

generated by fable 5

Test Plan

Updated snapshots. We already had some of our own tests that covered the affected syntax.

Docs

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Latest commit: 865b4d5

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Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	53430	53430	0
Passed	52149	52149	0
Failed	1239	1239	0
Panics	42	42	0
Coverage	97.60%	97.60%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	38	38	0
Passed	37	37	0
Failed	1	1	0
Panics	0	0	0
Coverage	97.37%	97.37%	0.00%

markdown/commonmark

Test result	main count	This PR count	Difference
Total	652	652	0
Passed	652	652	0
Failed	0	0	0
Panics	0	0	0
Coverage	100.00%	100.00%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	5467	5467	0
Passed	1915	1915	0
Failed	3552	3552	0
Panics	0	0	0
Coverage	35.03%	35.03%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	676	676	0
Passed	592	592	0
Failed	84	84	0
Panics	0	0	0
Coverage	87.57%	87.57%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	18876	18876	0
Passed	13010	13010	0
Failed	5865	5865	0
Panics	1	1	0
Coverage	68.92%	68.92%	0.00%

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 55868d49-c394-4aa1-8c8b-46671ac00ab3

📥 Commits

Reviewing files that changed from the base of the PR and between 865b4d5 and c86c648.

⛔ Files ignored due to path filters (3)

• crates/biome_yaml_formatter/tests/specs/prettier/yaml/flow-mapping/middle-comments.yml.snap is excluded by !**/*.snap and included by **
• crates/biome_yaml_formatter/tests/specs/prettier/yaml/flow-sequence/middle-comments.yml.snap is excluded by !**/*.snap and included by **
• crates/biome_yaml_formatter/tests/specs/yaml/flow/collection_key.yaml.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (6)

• crates/biome_yaml_formatter/src/yaml/auxiliary/block_map_implicit_entry.rs
• crates/biome_yaml_formatter/src/yaml/auxiliary/flow_map_explicit_entry.rs
• crates/biome_yaml_formatter/src/yaml/auxiliary/flow_map_implicit_entry.rs
• crates/biome_yaml_formatter/src/yaml/auxiliary/flow_mapping.rs
• crates/biome_yaml_formatter/src/yaml/auxiliary/flow_sequence.rs
• crates/biome_yaml_formatter/tests/specs/yaml/flow/collection_key.yaml

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/biome_yaml_formatter/src/yaml/auxiliary/block_map_implicit_entry.rs

---

Walkthrough

The YAML formatter adds flow-collection detection and optional trailing commas for flow-map entry lists. Flow mappings and entries now use structured, comment-aware layouts with controlled indentation, separators, and explicit ? key : value formatting. Implicit entries share helpers for collection keys, values, colon spacing, and comment-driven breaks. Comment placement recognises explicit flow-map entries, and a fixture covers collection-key formatting.

Possibly related PRs

• biomejs/biome#10814: Overlaps with comment-driven flow-sequence expansion.
• biomejs/biome#10873: Also changes flow-map entry-list rendering.

Suggested reviewers: ematipico

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: YAML flow mapping formatting.
Description check	✅ Passed	The description is directly related and accurately summarises the YAML flow mapping formatter work.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch dyc3/yaml-fmt-flow-mappings

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 Checkov (3.3.8)

crates/biome_yaml_formatter/tests/specs/yaml/flow/collection_key.yaml

Traceback (most recent call last):
File "/usr/local/bin/checkov", line 2, in
from checkov.main import Checkov
ModuleNotFoundError: No module named 'checkov'

---

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[dyc3]

• feat(format/yaml): block scalars #11019
• feat(format/yaml): flow mappings #11011 👈 (View in Graphite)
• main

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[ematipico]

Comments to review, and patterns to change.