dsfmt

Datastar expression formatter for HTML, JSX, and TSX. A thin adapter around the OXC formatter engine used by oxfmt.

Install

cargo install --locked --git https://github.com/hyperpuncher/dsfmt

Requires Rust 1.96 or newer.

Usage

# Format a file (prints to stdout)
dsfmt src/components/slider.tsx

# Write changes back
dsfmt --write src/components/slider.tsx

# Format all supported files in a directory
dsfmt --write src/

# Check if files are formatted (exit code 1 if changes needed)
dsfmt --check src/

# Read from stdin
cat file.html | dsfmt --stdin-filepath file.html

Options

Flag	Default	Description
--stdin-filepath	none	Use the filename to select HTML or JSX/TSX when reading stdin
--line-width	90	Expression print width
--use-spaces	false	Use spaces instead of tabs
--tab-width	4	Positive number of spaces per indent level
--write, -w	false	Atomically write changes, preserving permissions and symlinks
--check	false	Report all changed files or stdin, without writing or printing source

What it does

• Detects current Datastar and Rocket attributes, including data-star-* aliases
• Ignores generic non-Datastar attributes like data-testid
• Adapts Datastar actions (@post, etc.) to JavaScript for OXC, then restores them
• Delegates expression wrapping, objects, arrays, statements, comments, and indentation to OXC
• Keeps delimiters attached to object/array boundaries and single-statement templates; gives statement lists and other multiline expressions separate delimiter lines
• Preserves comma expressions rather than converting them to statements
• Preserves literal-valued attributes, multiline literal contents, and CRLF line endings
• Leaves unsupported expressions (including host-interpolated templates and kebab-case signals), unquoted HTML values, encoded expressions, and malformed tags intact
• Replaces only Datastar string/template value spans. Native JSX expressions, tag layout, ordinary attributes, and all other source bytes are untouched

Run dsfmt before oxfmt: dsfmt handles embedded Datastar expressions, while oxfmt owns host-file formatting. For stdin/editor integration, pass --stdin-filepath so the host language is selected without guessing.

Supported file types

HTML (including .htm), JSX, TSX, Templ, HEEx, Blade. Extensions are case-insensitive.

--write and --check are mutually exclusive. Read, write, and directory-walk failures exit nonzero. Directory scans respect ignore files and skip hidden files by default.

development

just full   # read-only formatting check, strict lint, and all tests
just fix    # apply formatting and lint fixes
just build  # locked release build
just bench  # repeatable release-mode formatter benchmark
just update # update dependency lockfile

The benchmark uses seven batches and reports median whole-format times for the fixtures and generated 100/1,000-attribute tags. It is not a timing assertion in the test suite.

The formatter does not implement its own expression splitting or tag reflow. Unsupported syntax is preserved rather than sent through a handwritten fallback.

Release notes are generated by scripts/release-notes.sh, grouped by conventional commit type.