Crate ezno_parser

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Ezno’s Parser

Contains “string to AST” parser, AST definitions, AST back to text/string form methods and hooks for traversing/visiting AST. Used in the Ezno checker.

This is more of an exercise project in getting better at writing Rust and doesn’t offer too much over other great Rust based JS parsers such as swc, rome, oxc and boa.

Goals:

  • Keep under 15k lines of code (excluding /tests and /examples folders)
  • Easy to use (see /tests and /examples folders)
  • Keep readable and maintainable
  • Designed for analysis and transformations
    • See expression identifiers can be used to bind information to
    • Retain source positions for throwing errors
    • All AST should be visitable. Immutably to collect facts or mutable to transform/remove
  • Optionally via configuration extend the ECMAscript language definition
    • TypeScript type annotations
      • Interfaces, enums and type alias statements
      • Parameter, return type and variable annotations
      • satisfies and as 😑
    • JSX support
      • Includes HTML comments, special handing of self closing tags from the specification
    • Others under feature = "extras" 👀

Non-goals

  • CSTs, close to source operations etc
    • Source with unbalanced parenthesis/brackets
  • Increase code size or decrease readability for speed improvements
  • Allow adding new syntax at runtime, that would require modifying the lexer at runtime adding new tokens

Features

Positions

All syntax has reference to where it was in the source using a Span. This uses the source-map crate, so it can generate source maps.

Identifiers

Most expressions, functions, blocks and some other AST has a unique identifier. This can be used to associate information with the node. For example Ezno’s checker associates type information with variable reference AST for later visitors or for hover information in the LSP.

“Cursors”

Allows holes in AST where a cursor exists. This allows for LSP to provide suggestions here while the whole source might not be valid.

Function extraction

All functions end up in a map rather than in the AST, which can make some static analysis and transformation operations easier.

Visiting

See example

Generator

Easily generate AST nodes with data interpolation using the constant compiled quasi-quoted macro. See example.

Notable structures

  • ASTNode, a trait that all AST should implement
  • FunctionBase, a abstraction for functions
  • Expression
  • Statements
  • Operators
  • TSXToken
  • TSXKeyword

Re-exports

Modules

Structs

Enums

Traits

  • ASTNode
    Defines common methods that would exist on a AST part include position in source, creation from reader and serializing to string from settings.
  • ExpressionOrStatementPosition
    Classes and function functions have two variants depending whether in statement position or expression position
  • IntoAST
    A trait which means that self can be pushed to a [TokenSender]
  • SelfVisitable
  • SelfVisitableMut
  • VariableFieldTypes
    Variable field can be used in type annotations but cannot have a value
  • Visitable
    For something to visitable it can visit all nested fields.
  • Visitor
    A visitor over something which is hooked/is SelfVisitable with some Data
  • VisitorMut
    A visitor over something which is hooked/is SelfVisitable with some Data
  • VisitorMutReceiver
    These are a receiver traits of the visitor
  • VisitorReceiver
    These are a receiver traits of the visitor

Functions

Type Definitions