refactor(markdown): emit continuation indent as structural CST node

[jfmcdowell]

Note

This PR was created with AI assistance (Claude Code).

Summary

Refs #9725.

Promote list continuation indent from trivia to an explicit MdContinuationIndent CST node. This gives the formatter structural access to continuation indentation instead of relying on trivia.

• Add MdContinuationIndent to grammar as an AnyMdLeafBlock
• Replace skip_line_indent with emit_line_indent wrapped in MdContinuationIndent for list continuation
• Skip MdContinuationIndent in HTML rendering and block iteration
• Fix render_fenced_code_block indent computation now that continuation indent is structural

Test Plan

• just test-crate biome_markdown_parser — all passed
• just test-crate biome_markdown_formatter — all passed
• just test-markdown-conformance — 652/652
• just f
• just l

Docs

N/A.

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Latest commit: 4745ed0

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[codspeed-hq]

Merging this PR will not alter performance

✅ 28 untouched benchmarks
⏩ 228 skipped benchmarks¹

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_{Comparing jfmcdowell:fix-md-continuation-indent-grammar (a75e2ca) with main (d94b8ac)}

Footnotes

1. 228 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

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📥 Commits

Reviewing files that changed from the base of the PR and between 4745ed0 and a75e2ca.

📒 Files selected for processing (2)

• crates/biome_markdown_parser/src/syntax/list.rs
• xtask/codegen/markdown.ungram

✅ Files skipped from review due to trivial changes (1)

• crates/biome_markdown_parser/src/syntax/list.rs

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

• xtask/codegen/markdown.ungram

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Walkthrough

The PR makes continuation-line indentation an explicit CST leaf by adding MdContinuationIndent across grammar, codegen, parser, formatter and HTML renderer. The parser now emits MD_CONTINUATION_INDENT instead of skipping the structural indent; codegen and kind registry include the new node; formatter rule and AsFormat/IntoFormat impls are added; AnyMdLeafBlock and HTML rendering are updated so continuation indents are treated as opaque/no-output leaf blocks. (≈70 words)

Possibly related PRs

• fix(markdown): fix fenced code block closing inside list items #9730 — implements MdContinuationIndent CST node and related parser/renderer wiring (directly overlaps grammar and renderer changes).
• fix(markdown): preserve nested list indent tokens #9717 — modifies continuation-indent handling in parser/formatter, touching the same parsing and formatting paths.
• test(markdown): add regression tests for mixed list markers across blank lines #9732 — adjusts list parsing logic and contains tests that exercise continuation-indent emission behavior.

Suggested reviewers

• ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarises the main change: promoting continuation indent from trivia to a structural CST node in the markdown parser/formatter.
Description check	✅ Passed	The description directly addresses the changeset, explaining the rationale, detailing specific changes across multiple files, and providing comprehensive test results.

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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/list.rs`:
- Around line 2039-2043: Add regression fixtures that reproduce and lock the CST
change where an explicit MdContinuationIndent node is emitted: create a parser
snapshot test for the `#9725` reproducer that ensures the CST contains
MD_CONTINUATION_INDENT produced by the code path using p.start(),
p.emit_line_indent(state.required_indent), and ci_m.complete(p,
MD_CONTINUATION_INDENT); additionally add a formatter snapshot for the same
input to ensure to_html stays no-output but the CST shape is preserved; include
both parser and formatter test files (valid case reproducer plus any minimal
error case if applicable) so the fix is covered by the test suite.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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Plan: Pro

Run ID: f1af8a13-0148-4b28-b2d9-036f9e7b3162

📥 Commits

Reviewing files that changed from the base of the PR and between 4a38b83 and 973ae6c.

⛔ Files ignored due to path filters (10)

• crates/biome_markdown_factory/src/generated/node_factory.rs is excluded by !**/generated/**, !**/generated/** and included by **
• crates/biome_markdown_factory/src/generated/syntax_factory.rs is excluded by !**/generated/**, !**/generated/** and included by **
• crates/biome_markdown_parser/tests/md_test_suite/ok/fenced_code_in_list.md.snap is excluded by !**/*.snap and included by **
• crates/biome_markdown_parser/tests/md_test_suite/ok/list_continuation_edge_cases.md.snap is excluded by !**/*.snap and included by **
• crates/biome_markdown_parser/tests/md_test_suite/ok/list_indentation.md.snap is excluded by !**/*.snap and included by **
• crates/biome_markdown_parser/tests/md_test_suite/ok/setext_heading_edge_cases.md.snap is excluded by !**/*.snap and included by **
• crates/biome_markdown_syntax/src/generated/kind.rs is excluded by !**/generated/**, !**/generated/** and included by **
• crates/biome_markdown_syntax/src/generated/macros.rs is excluded by !**/generated/**, !**/generated/** and included by **
• crates/biome_markdown_syntax/src/generated/nodes.rs is excluded by !**/generated/**, !**/generated/** and included by **
• crates/biome_markdown_syntax/src/generated/nodes_mut.rs is excluded by !**/generated/**, !**/generated/** and included by **

📒 Files selected for processing (9)

• crates/biome_markdown_formatter/src/generated.rs
• crates/biome_markdown_formatter/src/markdown/any/leaf_block.rs
• crates/biome_markdown_formatter/src/markdown/auxiliary/continuation_indent.rs
• crates/biome_markdown_formatter/src/markdown/auxiliary/mod.rs
• crates/biome_markdown_parser/src/syntax/list.rs
• crates/biome_markdown_parser/src/to_html.rs
• crates/biome_markdown_parser/tests/spec_test.rs
• xtask/codegen/markdown.ungram
• xtask/codegen/src/markdown_kinds_src.rs

💤 Files with no reviewable changes (1)

• crates/biome_markdown_parser/tests/spec_test.rs

[dyc3]

It's a bit hard for me to understand what a "Continuation Indent" is.

[jfmcdowell]

It's a bit hard for me to understand what a "Continuation Indent" is.

@dyc3 it is the whitespace that keeps continuation lines inside a list item (CommonMark §5.2). Example: the two spaces before bar in:

- foo
  bar

I added a clarifying comment.

[dyc3]

oh, i see, makes sense then