Mutable AST library for Hack with linting and code migrations
HHAST is a toolkit for processing the AST of Hack files.
Abstract syntax trees can be an extremely powerful basis for many kinds of tooling beyond compilers and optimization; HHAST is built on top of Hack's Full Fidelity Parser (FFP), providing a Hack object representation of a mutable AST.
Unlike traditional ASTs, the FFP's AST includes all 'trivia' - such as whitespace and comments - allowing you to fully recreate the file from the AST, or create an updated file after mutating the AST, preserving comments and whitespace.
HHAST has 3 main APIs:
Linters are designed for subjective or style changes which do not substantially alter the behavior of the code, and may be rejected on a case-by-case basis. Lint errors can provide a suggested fix, which may be based on an AST mutation, but doesn't have to be.
We've included several linters as a starting point, including:
<<__Override>>
where possibleLinters can be used both interactively, or unattended. Autofixing is not supported unattended, however it will exit with non-zero if there are any lint issues, to ease integration with CI systems.
HHAST is supported by:
Migrations are for sweeping changes you want to apply across your entire codebase, and are often more complex. Taking this into account, the migration framework has built-in support for multi-step migrations (unlike linters). AST-aware migrations can be a powerful tool for:
See the documentation.
HHAST is MIT-licensed.