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:
- a low-level library for inspecting and manipulating the FFP AST
- a linting framework, with support for auto-fixing linters
- a migration framework
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:
- don't use await in a loop
- methods should be ->lowerCamelCase(), functions should be under_scored()
- always use braces for control flow
- always use
Linters 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.
Editor and IDE Support
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:
- adjusting for changes to the language (for example, the shape changes described below)
- replacing deprecated APIs with new ones
- general clean-up of the codebase
Low-level AST library
See the documentation.
HHAST is MIT-licensed.