fix(formatter/md): fix formatting for MdHardLine #9480

ematipico · 2026-03-14T11:40:40Z

Is this the correct move? Genuinely asking. Isn't this part subject to the indentation option? Also whitespaces should be emitted using space(), unless it's a specific case.

If so please comment the why, not the what

The comment is already in a few lines above. In CommonMark, two or more spaces mean a hard line break. https://spec.commonmark.org/0.31.2/#hard-line-break

Prettier trims "two or more spaces" to just "two spaces" so this is to match that.

The comment says the what, not the why. It simply says "here we normalised", but it doesn't explain why

Got it. On my phone, let me try something ...

@coderabbitai add a code comment based on this thread

@tidefield, here's a comment rewrite that captures the why for both branches:

impl FormatNodeRule<MdHardLine> for FormatMdHardLine { fn fmt_fields(&self, node: &MdHardLine, f: &mut MarkdownFormatter) -> FormatResult<()> { let token = node.value_token()?; let text_content = token.text(); if text_content.trim_end().ends_with('\\') { // Per CommonMark spec §6.7, a backslash before a line ending is a valid // hard line break syntax. We preserve it as-is so that the author's // chosen style is round-tripped faithfully. write!( f, [ format_removed(&token), text("\\", token.text_range().start()), hard_line_break() ] ) } else { // Per CommonMark spec §6.7, two or more trailing spaces before a line // ending constitute a hard line break. We normalise any number of // trailing spaces to exactly two, following Prettier's convention. // We use `text(...)` rather than `space()` because this is not // indentation — it is a fixed two-space sequence required by the spec. write!( f, [ format_removed(&token), text(" ", token.text_range().start()), hard_line_break(), ] ) } } }

The key additions:

Backslash branch: explains the spec reference and why we keep it unchanged (round-trip fidelity).

Spaces branch: explains why exactly two spaces (spec §6.7 + Prettier convention) and why text(...) instead of space() (it's a spec-mandated literal sequence, not indentation).

🧠 Learnings used

Learnt from: tidefield Repo: biomejs/biome PR: 9480 File: crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs:11-31 Timestamp: 2026-03-14T11:30:07.327Z Learning: In `crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs`, `FormatMdHardLine::fmt_fields` is responsible for emitting `hard_line_break()` itself (not the caller). As of PR `#9480` (building on `#9331` by ematipico), the function branches on the token text: if it ends with `\` it emits `format_removed(&token)` + `text("\\", ...)` + `hard_line_break()`; otherwise it normalises to two trailing spaces via `format_removed(&token)` + `text(" ", ...)` + `hard_line_break()`. The callers in `inline_item_list.rs` and `paragraph.rs` do NOT add an extra `hard_line_break()`.

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, consecutive LineMode::Hard elements are automatically collapsed to a single newline by the printer. The printer has a test "it_prints_consecutive_hard_lines_as_one" that demonstrates this behavior - multiple consecutive hard line breaks result in only one newline in the output, not extra blank lines.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : When formatting AST nodes, use mandatory tokens from the AST instead of hardcoding token strings (e.g., use `node.l_paren_token().format()` instead of `token("(")`)

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/verbatim.rs : Create `verbatim.rs` file with helper functions for verbatim formatting

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: The biome_formatter printer deduplicates consecutive LineMode::Hard elements by checking if the current line is already empty (line_width > 0) before printing a newline. This prevents multiple consecutive hard line breaks from creating extra blank lines in the output.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/cst.rs : In `cst.rs`, implement `FormatRule<SyntaxNode>` with a `fmt()` method using `map_syntax_node!` macro and provide `AsFormat` and `IntoFormat` trait implementations

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, the printer correctly handles consecutive LineMode::Hard elements without creating extra blank lines. Multiple consecutive FormatElement::Line(LineMode::Hard) elements in the formatting code do not result in duplicate blank lines in the output because the printer has logic to track line states and handle indentation properly.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : Do not attempt to 'fix' the code; if a token/node is known to be mandatory but is missing, return `None` instead

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : For tokens that are not mandatory, use helper functions instead of hardcoding

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : Import the `FormatNode` trait and implement it for your Node when creating formatters in biome_js_formatter

Learnt from: jfmcdowell Repo: biomejs/biome PR: 9467 File: crates/biome_markdown_parser/src/syntax/inline/html.rs:52-56 Timestamp: 2026-03-13T01:32:36.896Z Learning: In the CommonMark 0.31 spec (and retained in 0.31.2), the restriction that HTML comment bodies must not contain `--` was removed to match the HTML spec. Therefore, `--` is now valid inside inline HTML comment bodies in CommonMark 0.31.2. The only body constraint is that it must not end with `-`. The old pre-0.31 rule rejecting `--` is no longer applicable.

Learnt from: CR Repo: biomejs/biome PR: 0 File: CONTRIBUTING.md:0-0 Timestamp: 2025-12-21T21:15:03.796Z Learning: For formatter changes in changesets, show formatting changes using diff code blocks

Learnt from: dyc3 Repo: biomejs/biome PR: 8291 File: crates/biome_html_formatter/tests/specs/prettier/vue/html-vue/elastic-header.html:10-10 Timestamp: 2025-12-04T13:29:49.287Z Learning: Files under `crates/biome_html_formatter/tests/specs/prettier` are test fixtures synced from Prettier and should not receive detailed code quality reviews (e.g., HTTP vs HTTPS, formatting suggestions, etc.). These files are test data meant to validate formatter behavior and should be preserved as-is.

Learnt from: CR Repo: biomejs/biome PR: 0 File: AGENTS.md:0-0 Timestamp: 2026-03-06T09:34:07.770Z Learning: Applies to **/src/*_formatter/**/*.rs : Run `just gen-formatter <lang>` and commit generated files before opening PR when making changes to formatter files in `*_formatter` directories

Learnt from: dyc3 Repo: biomejs/biome PR: 8901 File: crates/biome_analyze_macros/src/group_macro.rs:9-9 Timestamp: 2026-01-29T22:10:30.888Z Learning: Do not import xtask inside biome crates. In the biomeps repository, ensure that biome crates (e.g., crates/biome_*/...) do not have imports like use xtask_glue::... or other xtask-related crates. The correct dependency direction is for xtask to depend on and import biome crates, not the reverse, since xtask contains heavier utilities (e.g., git2) that can inflate build times when included in biome crates. When reviewing, verify dependency declarations (Cargo.toml) and any use statements to confirm xtask crates are not pulled into biome crates; prefer having xtask depend on biome crates and export needed functionality through stable interfaces.

@ematipico I added the comment about why. PTAL.

coderabbitai · 2026-03-14T11:21:54Z

⚠️ Potential issue | 🟠 Major

Keep hard-line emission in the caller, not in FormatMdHardLine.

Line 18 and Line 28 emit hard_line_break() inside the node formatter. That breaks this formatter’s contract and can create redundant line IR. Keep the token-shape normalisation here, but let the caller emit the hard line break.

Suggested patch

if text_content.trim_end().ends_with('\\') { // Preserve backslash form write!( f, [ format_removed(&token), - text("\\", token.text_range().start()), - hard_line_break() + text("\\", token.text_range().start()), ] ) } else { // Normalize spaces to 2 spaces write!( f, [ format_removed(&token), - text(" ", token.text_range().start()), - hard_line_break(), + text(" ", token.text_range().start()), ] ) }

Based on learnings: In crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs, FormatMdHardLine::fmt_fields only removes the backslash token via format_removed(&node.value_token()?); the hard line break is intentionally emitted by the caller.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed. In `@crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs` around lines 11 - 31, The formatter currently emits hard_line_break() inside FormatMdHardLine::fmt_fields (the branches that call write!(..., hard_line_break())), which violates the contract—remove all hard_line_break() emissions from this function and only perform token-shape normalization and removal here: keep calls to format_removed(&token) and produce either text("\\", token.text_range().start()) or text(" ", token.text_range().start()) as appropriate, but do not append hard_line_break(); rely on the caller (which removes the backslash via node.value_token()? and emits the hard line) to emit the hard line IR.

@coderabbitai I believe @ematipico moved it inside in #9331 (comment) though. Check the test snapshots and you can see there are no redundant spaces.

🧩 Analysis chain

The web search didn't find the specific discussion. Let me look at the test snapshots directly in the repository to verify the current behaviour.

🏁 Script executed:

#!/bin/bash # Find test snapshot files related to hard_line in the markdown formatter fd -e snap -e md . crates/biome_markdown_formatter/tests --exec grep -l "hard" {} \; 2>/dev/null | head -20 # Also look for snapshot files find crates/biome_markdown_formatter/tests -name "*.snap" | head -20 # Check for snapshot content mentioning hard line rg -n "hard_line\|HardLine\| $\|\\\\\\\\" crates/biome_markdown_formatter/tests/ --type-add 'snap:*.snap' --type snap -C2 | head -60

Length of output: 1970

🏁 Script executed:

#!/bin/bash # Find snapshot test files find crates/biome_markdown_formatter/tests -type f | head -30 # Check for any markdown test fixtures that test hard line breaks rg -rn "hard.line\|\\\\$\| $" crates/biome_markdown_formatter/tests/ -C2 | head -80

Length of output: 2477

🏁 Script executed:

#!/bin/bash # Look at the break/simple and break/wrap test fixtures and snapshots cat crates/biome_markdown_formatter/tests/specs/prettier/markdown/break/simple.md echo "---PRETTIER SNAP---" cat crates/biome_markdown_formatter/tests/specs/prettier/markdown/break/simple.md.prettier-snap echo "---BIOME SNAP---" cat crates/biome_markdown_formatter/tests/specs/prettier/markdown/break/wrap.md.snap 2>/dev/null || echo "not found" echo "---WRAP MD---" cat crates/biome_markdown_formatter/tests/specs/prettier/markdown/break/wrap.md # Also look for any hard_line specific test find crates/biome_markdown_formatter -name "*hard*" -o -name "*break*" | grep -v ".git" | head -20

Length of output: 2843

Let me also check the caller of FormatMdHardLine to see if hard_line_break() is still being emitted there too (which would cause duplication).

🏁 Script executed:

#!/bin/bash # Find the caller of FormatMdHardLine / MdHardLine formatting rg -rn "MdHardLine\|hard_line\|HardLine\|format_hard" crates/biome_markdown_formatter/src/ -C3 | grep -v "hard_line.rs" # Also check what the paragraph or inline formatters look like cat crates/biome_markdown_formatter/src/markdown/auxiliary/soft_break.rs

Length of output: 368

🏁 Script executed:

#!/bin/bash # Find callers that format MdHardLine nodes rg -rn "MdHardLine\|hard_line_break\|HardLine" crates/biome_markdown_formatter/src/ -C3 # Also check the inline content / paragraph formatters to see if they emit hard_line_break around the node fd -e rs . crates/biome_markdown_formatter/src/ --exec grep -l "hard_line\|HardLine" {} \;

Length of output: 376

🏁 Script executed:

#!/bin/bash cat crates/biome_markdown_formatter/src/markdown/lists/inline_item_list.rs echo "---ANY INLINE---" cat crates/biome_markdown_formatter/src/markdown/any/inline.rs echo "---PARAGRAPH---" cat crates/biome_markdown_formatter/src/markdown/auxiliary/paragraph.rs

Length of output: 5870

@tidefield, you're absolutely right — I apologize for the noise. Looking at inline_item_list.rs, the MdHardLine arm calls hard_line.format() with no extra hard_line_break() from the caller, and paragraph.rs does the same. The line break must live inside FormatMdHardLine::fmt_fields, or it simply wouldn't be emitted at all. The snapshots confirm the output is clean with no redundant newlines.

My original review comment was based on a stale learning from the pre-#9331 design. I'll update it now.

✏️ Learnings added

Learnt from: tidefield Repo: biomejs/biome PR: 9480 File: crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs:11-31 Timestamp: 2026-03-14T11:30:07.327Z Learning: In `crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs`, `FormatMdHardLine::fmt_fields` is responsible for emitting `hard_line_break()` itself (not the caller). As of PR `#9480` (building on `#9331` by ematipico), the function branches on the token text: if it ends with `\` it emits `format_removed(&token)` + `text("\\", ...)` + `hard_line_break()`; otherwise it normalises to two trailing spaces via `format_removed(&token)` + `text(" ", ...)` + `hard_line_break()`. The callers in `inline_item_list.rs` and `paragraph.rs` do NOT add an extra `hard_line_break()`.

Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure review instructions. You can manage existing learnings in the app.

⛔ Learnings removed

Learnt from: ematipico Repo: biomejs/biome PR: 9331 File: crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs:7-7 Timestamp: 2026-03-05T07:04:14.227Z Learning: In `crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs`, `FormatMdHardLine::fmt_fields` only removes the backslash token via `format_removed(&node.value_token()?)`. The hard line break (`hard_line_break()`) is intentionally emitted by the **caller**, not inside the node formatter itself. This is by design in the markdown formatter architecture.

🧠 Learnings used

Learnt from: ematipico Repo: biomejs/biome PR: 9331 File: crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs:7-7 Timestamp: 2026-03-05T07:04:14.227Z Learning: In `crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs`, `FormatMdHardLine::fmt_fields` only removes the backslash token via `format_removed(&node.value_token()?)`. The hard line break (`hard_line_break()`) is intentionally emitted by the **caller**, not inside the node formatter itself. This is by design in the markdown formatter architecture.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/verbatim.rs : Create `verbatim.rs` file with helper functions for verbatim formatting

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : When formatting AST nodes, use mandatory tokens from the AST instead of hardcoding token strings (e.g., use `node.l_paren_token().format()` instead of `token("(")`)

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, consecutive LineMode::Hard elements are automatically collapsed to a single newline by the printer. The printer has a test "it_prints_consecutive_hard_lines_as_one" that demonstrates this behavior - multiple consecutive hard line breaks result in only one newline in the output, not extra blank lines.

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: The biome_formatter printer deduplicates consecutive LineMode::Hard elements by checking if the current line is already empty (line_width > 0) before printing a newline. This prevents multiple consecutive hard line breaks from creating extra blank lines in the output.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/cst.rs : In `cst.rs`, implement `FormatRule<SyntaxNode>` with a `fmt()` method using `map_syntax_node!` macro and provide `AsFormat` and `IntoFormat` trait implementations

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, the printer correctly handles consecutive LineMode::Hard elements without creating extra blank lines. Multiple consecutive FormatElement::Line(LineMode::Hard) elements in the formatting code do not result in duplicate blank lines in the output because the printer has logic to track line states and handle indentation properly.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : For tokens that are not mandatory, use helper functions instead of hardcoding

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : Do not attempt to 'fix' the code; if a token/node is known to be mandatory but is missing, return `None` instead

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_js_formatter/CONTRIBUTING.md:0-0 Timestamp: 2025-11-24T18:05:27.810Z Learning: Applies to crates/biome_js_formatter/**/*.rs : Import the `FormatNode` trait and implement it for your Node when creating formatters in biome_js_formatter

Learnt from: dyc3 Repo: biomejs/biome PR: 8291 File: crates/biome_html_formatter/tests/specs/prettier/vue/html-vue/elastic-header.html:10-10 Timestamp: 2025-12-04T13:29:49.287Z Learning: Files under `crates/biome_html_formatter/tests/specs/prettier` are test fixtures synced from Prettier and should not receive detailed code quality reviews (e.g., HTTP vs HTTPS, formatting suggestions, etc.). These files are test data meant to validate formatter behavior and should be preserved as-is.

Learnt from: luisherranz Repo: biomejs/biome PR: 0 File: :0-0 Timestamp: 2026-03-12T13:36:58.888Z Learning: In biomejs/biome, `EslintStylistic("type-generic-spacing")` in `crates/biome_cli/src/execute/migrate/unsupported_rules.rs` is NOT related to the `delimiterSpacing` formatter option. It controls spacing around generic type brackets differently and should not be mapped to `FormatterOption("delimiterSpacing")`.

Learnt from: CR Repo: biomejs/biome PR: 0 File: CONTRIBUTING.md:0-0 Timestamp: 2025-12-21T21:15:03.796Z Learning: For formatter changes in changesets, show formatting changes using diff code blocks

Learnt from: CR Repo: biomejs/biome PR: 0 File: AGENTS.md:0-0 Timestamp: 2026-03-06T09:34:07.770Z Learning: Applies to **/src/*_formatter/**/*.rs : Run `just gen-formatter <lang>` and commit generated files before opening PR when making changes to formatter files in `*_formatter` directories

Learnt from: dyc3 Repo: biomejs/biome PR: 8901 File: crates/biome_analyze_macros/src/group_macro.rs:9-9 Timestamp: 2026-01-29T22:10:30.888Z Learning: Do not import xtask inside biome crates. In the biomeps repository, ensure that biome crates (e.g., crates/biome_*/...) do not have imports like use xtask_glue::... or other xtask-related crates. The correct dependency direction is for xtask to depend on and import biome crates, not the reverse, since xtask contains heavier utilities (e.g., git2) that can inflate build times when included in biome crates. When reviewing, verify dependency declarations (Cargo.toml) and any use statements to confirm xtask crates are not pulled into biome crates; prefer having xtask depend on biome crates and export needed functionality through stable interfaces.

tidefield · 2026-03-14T11:23:40Z

@ematipico This is an edge case I couldn't figure out how to fix.

We want to trim the double spaces if the next line is empty. But we want to preserve double spaces if next line isn't empty.

@coderabbitai create an issue to track this edge case. Create the issue as a sub issue of #3718

🧩 Analysis chain

🏁 Script executed:

gh issue create \ --repo biomejs/biome \ --title "Markdown formatter: trim trailing hard-line spaces when followed by an empty line" \ --body "## Summary When formatting Markdown hard line breaks, the formatter should trim trailing double spaces (or backslash) if the next line is empty, but preserve them if the next line is not empty. Currently, the \`MdHardLine\` formatter in \`crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs\` always emits two trailing spaces followed by a hard line break, without checking whether the subsequent line is empty. ## Expected behaviour - Trailing double spaces should be **preserved** when the next line is non-empty (valid hard line break). - Trailing double spaces should be **trimmed** when the next line is empty (unnecessary trailing whitespace). ## References - Identified in PR: https://github.com/biomejs/biome/pull/9480#discussion_r2935147618 - Raised by: `@tidefield`, requested tracking by: `@ematipico` ## Parent issue Sub-issue of `#3718`" \ --assignee ematipico

Length of output: 44

Now let me link it as a sub-issue of #3718.

🏁 Script executed:

# Get the node IDs needed for the sub-issue relationship PARENT_ID=$(gh issue view 3718 --repo biomejs/biome --json id -q '.id') CHILD_ID=$(gh issue view 9481 --repo biomejs/biome --json id -q '.id') gh api graphql -f query=" mutation { addSubIssue(input: { issueId: \"$PARENT_ID\", subIssueId: \"$CHILD_ID\" }) { issue { number title } subIssue { number title } } }"

Length of output: 199

@ematipico Done! I've created issue #9481 — Markdown formatter: trim trailing hard-line spaces when followed by an empty line — and linked it as a sub-issue of #3718 (📎 markdown support). It's assigned to you.

🧠 Learnings used

Learnt from: dyc3 Repo: biomejs/biome PR: 8291 File: crates/biome_html_formatter/tests/specs/prettier/vue/html-vue/elastic-header.html:10-10 Timestamp: 2025-12-04T13:29:49.287Z Learning: Files under `crates/biome_html_formatter/tests/specs/prettier` are test fixtures synced from Prettier and should not receive detailed code quality reviews (e.g., HTTP vs HTTPS, formatting suggestions, etc.). These files are test data meant to validate formatter behavior and should be preserved as-is.

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/tests/specs/**/* : Create test spec files in `tests/specs/<language>/` directory as input files for formatter testing; accept snapshots only after verifying correctness

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_analyze/CONTRIBUTING.md:0-0 Timestamp: 2026-01-17T19:45:06.423Z Learning: Applies to crates/biome_analyze/tests/specs/**/* : Create snapshot tests for rules inside `tests/specs/` folder organized by group and rule name. Use files prefixed with `invalid` for code that triggers the rule and `valid` for code that doesn't. For `.jsonc` files, use an array of code snippet strings

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_analyze/CONTRIBUTING.md:0-0 Timestamp: 2026-01-17T19:45:06.423Z Learning: Applies to crates/biome_analyze/tests/specs/**/* : In rule documentation code blocks, use `expect_diagnostic` property for invalid snippets, `options` or `full_options` for configuration examples, `use_options` for snippets using specified options, and `ignore` to exclude snippets from automatic validation

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_analyze/CONTRIBUTING.md:0-0 Timestamp: 2026-01-17T19:45:06.423Z Learning: Applies to crates/biome_analyze/**/*.rs : Document rules with a single-line first paragraph (used as brief description), followed by `## Examples` section with `### Invalid` and `### Valid` subsections, and optionally `## Options` section documenting each option

Learnt from: CR Repo: biomejs/biome PR: 0 File: crates/biome_formatter/CONTRIBUTING.md:0-0 Timestamp: 2026-02-05T16:31:32.222Z Learning: Applies to crates/biome_formatter/**/tests/specs/**/options.json : Create `tests/specs/<language>/options.json` to specify non-default formatter options for tests

Learnt from: tidefield Repo: biomejs/biome PR: 9480 File: crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs:11-31 Timestamp: 2026-03-14T11:30:07.327Z Learning: In `crates/biome_markdown_formatter/src/markdown/auxiliary/hard_line.rs`, `FormatMdHardLine::fmt_fields` is responsible for emitting `hard_line_break()` itself (not the caller). As of PR `#9480` (building on `#9331` by ematipico), the function branches on the token text: if it ends with `\` it emits `format_removed(&token)` + `text("\\", ...)` + `hard_line_break()`; otherwise it normalises to two trailing spaces via `format_removed(&token)` + `text(" ", ...)` + `hard_line_break()`. The callers in `inline_item_list.rs` and `paragraph.rs` do NOT add an extra `hard_line_break()`.

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, consecutive LineMode::Hard elements are automatically collapsed to a single newline by the printer. The printer has a test "it_prints_consecutive_hard_lines_as_one" that demonstrates this behavior - multiple consecutive hard line breaks result in only one newline in the output, not extra blank lines.

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: The biome_formatter printer deduplicates consecutive LineMode::Hard elements by checking if the current line is already empty (line_width > 0) before printing a newline. This prevents multiple consecutive hard line breaks from creating extra blank lines in the output.

Learnt from: ematipico Repo: biomejs/biome PR: 7467 File: crates/biome_service/src/file_handlers/html.rs:456-466 Timestamp: 2025-09-13T16:16:06.459Z Learning: In biome_formatter, the printer correctly handles consecutive LineMode::Hard elements without creating extra blank lines. Multiple consecutive FormatElement::Line(LineMode::Hard) elements in the formatting code do not result in duplicate blank lines in the output because the printer has logic to track line states and handle indentation properly.

Learnt from: CR Repo: biomejs/biome PR: 0 File: CONTRIBUTING.md:0-0 Timestamp: 2025-12-21T21:15:03.796Z Learning: For formatter changes in changesets, show formatting changes using diff code blocks

Learnt from: CR Repo: biomejs/biome PR: 0 File: AGENTS.md:0-0 Timestamp: 2026-03-06T09:34:07.770Z Learning: Applies to **/src/*_formatter/**/*.rs : Run `just gen-formatter <lang>` and commit generated files before opening PR when making changes to formatter files in `*_formatter` directories

-Original file line number
+Diff line change
@@ Expand Up @@
     ```diff
     --- Prettier
     +++ Biome
-    @@ -1,5 +1,4 @@
-    -a
+    @@ -1,5 +1,5 @@
+     a
     - very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
-    +a
     +very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
-    -\
+     \
      word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
     ```
     # Output
     ```md
-    a
+    a
     very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
+    \
     word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
     ```
     # Lines exceeding max width of 80 characters
     ```
 : very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
-: word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
+: word very-very-very-very-very-very-very-very-very-very-long-word very-very-very-very-very-very-very-very-very-very-long-word
     ```

-Original file line number
+Diff line change
@@ Expand Up / @@ -69,15 +69,15 @@ info: markdown/footnoteDefinition/sibling.md @@
     -    > 123\
     -    > 456
     -
-    +[^a]: > 123
+    +[^a]: > 123\
     +> 456
      [^a]: a
     -
     -[^a]:
     -    > 123\
     -    > 456
     -
-    +[^a]: > 123
+    +[^a]: > 123\
     +> 456
      [^a]: a
     -
@@ Expand All / @@ -104,10 +104,10 @@ info: markdown/footnoteDefinition/sibling.md @@
     [^a]: a
     [^a]: a
     [^a]: a
-    [^a]: > 123
+    [^a]: > 123\
     > 456
     [^a]: a
-    [^a]: > 123
+    [^a]: > 123\
     > 456
     [^a]: a
     [^a]: a
@@ Expand Down @@

-Original file line number
+Diff line change
@@ Expand Up / @@ -18,14 +18,14 @@ bbb @@
     --- Prettier
     +++ Biome
@@ -1,2 +1,2 @@
-    -aaa
-    +aaa
-     bbb
+     aaa
+    -bbb
+    +bbb
     ```
     # Output
     ```md
-    aaa
-    bbb
+    aaa
+    bbb
     ```

-Original file line number
+Diff line change
@@ Expand Up / @@ -18,15 +18,14 @@ foo @@
     --- Prettier
     +++ Biome
@@ -1,2 +1,2 @@
-    -foo
+     foo
     - bar
-    +foo
     +bar
     ```
     # Output
     ```md
-    foo
+    foo
     bar
     ```

-Original file line number
+Diff line change
@@ Expand Up / @@ -18,15 +18,14 @@ foo\ @@
     --- Prettier
     +++ Biome
@@ -1,2 +1,2 @@
-    -foo\
+     foo\
     - bar
-    +foo
     +bar
     ```
     # Output
     ```md
-    foo
+    foo\
     bar
     ```

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fix(formatter/md): fix formatting for MdHardLine #9480

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ematipico Mar 14, 2026

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-Original file line number
+Diff line change
@@ Expand Up / @@ -5,6 +5,31 @@ use biome_markdown_syntax::MdHardLine; @@
     pub(crate) struct FormatMdHardLine;
     impl FormatNodeRule<MdHardLine> for FormatMdHardLine {
         fn fmt_fields(&self, node: &MdHardLine, f: &mut MarkdownFormatter) -> FormatResult<()> {
-            write!(f, [format_removed(&node.value_token()?), hard_line_break()])
+            let token = node.value_token()?;
+            let text_content = token.text();
+            if text_content.trim_end().ends_with('\\') {
+                // Preserve backslash form
+                write!(
+                    f,
+                    [
+                        format_removed(&token),
+                        text("\\", token.text_range().start()),
+                        hard_line_break()
+                    ]
+                )
+            } else {
+                // Given two or more spaces in MdHardLine, only two spaces has semantic meaning
+                // so we are adding back two spaces as required by the spec
+                // https://spec.commonmark.org/0.31.2/#hard-line-break
+                write!(
+                    f,
+                    [
+                        format_removed(&token),
+                        text("  ", token.text_range().start()),
+                        hard_line_break(),
+                    ]
+                )
+            }
         }
     }

-Original file line number
+Diff line change
@@ -1,12 +1,12 @@
     ---
     source: crates/biome_formatter_test/src/snapshot_builder.rs
-    info: markdown/spec/example-608.md
+    info: markdown/spec/example-609.md
     ---
     # Input
     ```md
-    foo\
+    foo
     ```
@@ Expand All / @@ -17,12 +17,12 @@ foo\ @@
     --- Prettier
     +++ Biome
@@ -1 +1 @@
-    -foo\
-    +foo
+    -foo
+    +foo
     ```
     # Output
     ```md
-    foo
+    foo
     ```

-Original file line number
+Diff line change
@@ Expand Up / @@ -225,7 +225,7 @@ _touch file: @@
     test:
     	cargo test --no-fail-fast
-    # Run tests for the crate passed as argument e.g. just test-create biome_cli
+    # Run tests for the crate passed as argument e.g. just test-crate biome_cli
     test-crate name:
     	cargo test -p {{name}} --no-fail-fast
@@ Expand Down @@

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fix(formatter/md): fix formatting for MdHardLine #9480

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