gorgeous

Grammar-driven pretty-printers for structured languages. Each language is defined by a BBNF grammar file — #[derive(Parser)] generates the parser, @pretty directives control formatting, and pprint renders the final output.

Usage

use gorgeous::{prettify_json, prettify_css, PrinterConfig};

let config = PrinterConfig { max_width: 80, indent: 2, use_tabs: false };

let formatted_json = prettify_json(input, &config);
let formatted_css = prettify_css(input, &config);

Partial formatting via source range:

use gorgeous::{prettify_json_range, PrinterConfig};

let config = PrinterConfig { max_width: 80, indent: 2, use_tabs: false };
let formatted = prettify_json_range(input, 100..200, &config);

Languages

All 37 tests pass. Idempotency verified: prettify(prettify(x)) == prettify(x).

CLI

Built-in languages auto-detect by extension; arbitrary languages JIT-compile from any .bbnf grammar.

gorg input.json                        # built-in, auto-detect by extension
gorg --lang css input.css              # built-in, explicit language
gorg --grammar my.bbnf input.txt       # JIT: any grammar, instant prettifier
gorg --grammar my.bbnf -r expr in.txt  # JIT with explicit entry rule
echo '{}' | gorg --lang json           # stdin
gorg input.css -o output.css           # write to file
gorg -w 120 -i 2 input.json            # custom width + indent
gorg --clear-cache                     # purge JIT cache

The JIT pipeline parses the .bbnf, generates a Cargo project with #[derive(Parser, prettify)], compiles it once, and caches the binary by content hash in ~/.cache/gorgeous/. Second run is instant.

Architecture

Grammar (.bbnf)
  → #[derive(Parser)]     proc-macro codegen (bbnf-derive)
    → AST (enum)           typed parse tree
      → to_doc()           @pretty-directed Doc emission
        → Doc tree         pprint intermediate representation
          → pprint()       Wadler-Lindig-inspired pretty-printer
            → String       formatted output

Alternative: VM interpreter (feature = "vm")
  Grammar (.bbnf) → bbnf-ir bytecode → runtime interpret → Doc tree → pprint()

The @pretty directives annotate grammar rules with formatting hints:

range_to_doc() enables partial formatting: nodes outside the target range emit verbatim source text, nodes inside emit formatted Doc trees.

Performance

End-to-end cached throughput (parse + to_doc + render):

Phase breakdown (bootstrap 281KB):

The derive path uses zero hand-written formatting code—all formatting is grammar-driven via @pretty directives and split_balanced() for format-time balanced splitting. The VM path interprets bbnf-ir bytecode at runtime for grammars not compiled via #[derive(Parser)].

Dependencies

All from crates.io:

• parse_that — parser combinators
• bbnf_derive — #[derive(Parser)] proc-macro
• bbnf — grammar analysis
• pprint — Wadler-Lindig pretty-printer

Dev: bencher for [[bench]] harness, biome_css_parser/biome_css_formatter v0.4.0 (benchmark competitor).

Build

cargo test --lib                # 37 tests
cargo test --lib --features vm  # + VM tests
cargo bench --bench gorgeous    # 51 benchmarks (JSON + CSS + GS + biome, phase splits)
cargo clippy -- -D warnings

Requires Rust nightly (#![feature(cold_path)]).