refactor(markdown-parser): simplify inline newline handling

[jfmcdowell]

Note

AI Assistance Disclosure: This PR was developed with assistance from Claude Code.

Summary

Refactor handle_inline_newline into smaller helpers so paragraph newline handling is easier to follow and review without changing markdown parsing behavior.

• Extract helpers for newline text emission, quote blank-line detection, quote-prefix breaks, setext breaks, list interrupts, and continuation indent emission.
• Document side-effecting boolean helpers with doc comments referencing CommonMark spec sections.
• Add focused regression coverage for nested list interruption after an inline newline.

Test Plan

• just test-crate biome_markdown_parser
• just test-markdown-conformance (652/652, 100%)
• just f && just l

Docs

N/A — internal parser refactor with no user-facing behavior change.

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Latest commit: fafc828

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• crates/biome_markdown_parser/src/syntax/mod.rs
• crates/biome_markdown_parser/tests/spec_test.rs

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Walkthrough

Refactors inline-newline handling in crates/biome_markdown_parser/src/syntax/mod.rs by extracting inlined branches into pub(crate) helper functions for newline-as-text emission, quote blank-line detection and prefix consumption, setext interruption checks, list-interrupt decisions, and inline-continuation indent emission. handle_inline_newline now orchestrates these helpers with equivalent observable behaviour. Adds tests for nested list interruption after a newline.

Possibly related PRs

• refactor(markdown-parser): align newline/prescan paragraph-break checks #9197 — Refactors newline and paragraph-break logic in the same module, aligning quote/list-interruption predicates.
• refactor(markdown-parser): promote fenced code block skipped trivia to explicit CST nodes #9321 — Touches quote-prefix consumption and MdIndentToken emission used by the new helpers.
• fix(markdown-parser): promote blockquote prefix markers from skipped trivia to explicit CST nodes #9219 — Modifies blockquote prefix detection/consumption logic that the new helpers interact with.

Suggested reviewers

• ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately summarises the main refactoring work—extracting inline newline handling into smaller helper functions without changing observable behaviour.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the refactoring, listing extracted helpers, and detailing the test plan and regression coverage added.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@crates/biome_markdown_parser/src/syntax/mod.rs`:
- Around line 920-932: The setext-detection path after computing real_indent
currently only accepts the underline if it begins immediately, which drops cases
like "- foo\n   ---"; update the lookahead/handling so that after confirming the
underline (the p.lookahead closure checking MD_SETEXT_UNDERLINE_LITERAL or
MD_THEMATIC_BREAK_LITERAL via is_dash_only_thematic_break) you perform the same
0–3-space probe used by the non-list path (i.e., consume up to three optional
spaces with p.skip_line_indent or equivalent) before returning true and calling
p.emit_indent_tokens; ensure emitted indent tokens reflect required_indent plus
any consumed optional spaces so the optional setext indent is preserved.

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Reviewing files that changed from the base of the PR and between f2debed and 198a9b1.

⛔ Files ignored due to path filters (1)

• crates/biome_markdown_parser/tests/md_test_suite/ok/nested_list_interrupt_after_newline.md.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (3)

• crates/biome_markdown_parser/src/syntax/mod.rs
• crates/biome_markdown_parser/tests/md_test_suite/ok/nested_list_interrupt_after_newline.md
• crates/biome_markdown_parser/tests/spec_test.rs