Readme.md

syntect

syntect is a work-in-progress syntax highlighting library for Rust that uses Sublime Text syntax definitions. It is not quite complete but eventually the goal is for it to be used in code analysis tools and text editors.

If you are writing a text editor (or something else needing highlighting) in Rust and this library doesn't fit your needs, I consider that a bug and you should file an issue or email me.

It is currently mostly complete and can parse, interpret and highlight based on Sublime Text syntax and tmTheme files.

Goals

• Work with many languages (accomplished through using existing grammar formats)
• Be super fast
• API that is both easy to use, and allows use in fancy text editors with piece tables and incremental re-highlighting and the like
• Expose internals of the parsing process so text editors can do things like cache parse states and use semantic info for code intelligence
• High quality highlighting, supporting things like heredocs and complex syntaxes (like Rust's).

Screenshots

There's currently an example program called syncat that prints one of the source files using hard-coded themes and syntaxes using 24-bit terminal escape sequences supported by many newer terminals. These screenshots don't look as good as they could for two reasons: first the sRGB colours aren't corrected properly, and second the Rust syntax definition uses some fancy labels that these themes don't have highlighting for.

Roadmap

• Sketch out representation of a Sublime Text syntax
• Parse .sublime-syntax files into the representation.
• Write an interpreter for the .sublime-syntax state machine that highlights an incoming iterator of file lines into an iterator of scope-annotated text.
• Parse TextMate/Sublime Text theme files
• Highlight a scope-annotated iterator into a colour-annotated iterator for display.
• Add nice API wrappers for simple use cases. The base APIs are designed for deep high performance integration with arbitrary text editor data structures.
• Make syncat a better demo, and maybe more demo programs
• Document the API better and make things private that don't need to be public
• Add sRGB colour correction (not sure if this is necessary, could be the job of the text editor)
• Make it really fast (mosty two hot-paths need caching, same places Textmate 2 caches)
• Add C bindings so it can be used as a C library from other languages.

Performance

Currently syntect is reasonably fast but not as fast as it could be. The following perf features are done and to-be-done:

• Pre-link references between languages (e.g <script> tags) so there are no tree traversal string lookups in the hot-path
• Compact binary representation of scopes to allow quickly passing and copying them around
• Determine if a scope is a prefix of another scope using bit manipulation in only a few instructions
• Cache regex matches to reduce number of times oniguruma is asked to search a line
• Cache scope lookups to reduce how much scope matching has to be done to highlight a list of scope operations
• Lazily compile regexes so startup time isn't taken compiling a thousand regexs for Actionscript that nobody will use
• Use a better regex engine, perhaps the in progress fancy-regex crate

The current perf numbers are below. These numbers should get better once I implement more of the things above, but they're on par with many other text editors.

• Highlighting 9200 lines of jQuery 2.1 takes 1.76s. For comparison:
  • Textmate 2, Spacemacs and Visual Studio Code all take around the same time (2ish seconds)
  • Atom takes 6s
  • Sublime Text 3 dev build takes ~0.22s, despite having a super fancy javascript syntax definition
  • Vim is instantaneous but that isn't a fair comparison since vim's highlighting is far more basic than the other editors.
  • These comparisons aren't totally fair, except the one to Sublime Text since that is using the same theme and the same complex defintion for ES6 syntax.
• ~220ms to load and link all the syntax definitions in the default Sublime package set. This is ~60% regex compilation and ~35% YAML parsing.
• ~1.9ms to parse and highlight the 30 line 791 character testdata/highlight_test.erb file. This works out to around 16,000 lines/second or 422 kilobytes/second.
• ~250ms end to end for syncat to start, load the definitions, highlight the test file and shut down. This is mostly spent loading.

License and Acknowledgements

Thanks to Textmate 2 and @defuz's sublimate for the existing open source code I used as inspiration and in the case of sublimate's tmTheme loader, copy-pasted. All code (including defuz's sublimate code) is released under the MIT license.