Rust grammar for tree-sitter

• Speed - When initially parsing a file, tree-sitter-rust takes around twice as long as Rustc's hand-coded parser.

  $ wc -l examples/ast.rs
    2157 examples/ast.rs
  
  $ rustc -Z ast-json-noexpand -Z time-passes examples/ast.rs | head -n1
    time: 0.007	parsing # (7 ms)
  
  $ tree-sitter parse examples/ast.rs --quiet --time
    examples/ast.rs	16 ms

  But if you edit the file after parsing it, this parser can generally update the previous existing syntax tree to reflect your edit in less than a millisecond, thanks to Tree-sitter's incremental parsing system.

• The Rust Grammar Reference - The grammar reference provides chapters that formally define the language grammar.
• The Rust Reference - While Rust does not have a specification, the reference tries to describe its working in detail. It tends to be out of date.
• Syntax Index - This appendix from The Book contains examples of all syntax in Rust cross-referenced with the section of The Book that describes it.