The parser uses an abstraction over non-whitespace tokens. This allows us to losslessly or lossly parse code without requiring explicit handling of whitespace. The parser yields events, not an AST, the events are resolved into untyped syntax nodes, which can then be casted into a typed AST.
The parser is able to produce a valid AST from any source code.
Erroneous productions are wrapped into
ERROR syntax nodes, the original source code
is completely represented in the final syntax nodes.
You probably do not want to use the parser struct, unless you want to parse fragments of Js source code or make your own productions.
Instead use functions such as
parse_text_lossy which offer abstracted versions for parsing.
Notable features of the parser are:
- Extremely fast parsing and lexing through the extremely fast
- Ability to do Lossy or Lossless parsing on demand without explicit whitespace handling.
- Customizable, able to parse any fragments of JS code at your discretion.
- Completely error tolerant, able to produce an AST from any source code.
- Zero cost for converting untyped nodes to a typed AST.
- Ability to go from AST to SyntaxNodes to SyntaxTokens to source code and back very easily with nearly zero cost.
- Very easy tree traversal through
- Descriptive errors with multiple labels and notes.
- Very cheap cloning, cloning an ast node or syntax node is the cost of adding a reference to an Rc.
- Cheap incremental reparsing of changed text.
The crate further includes utilities such as:
- ANSI syntax highlighting of nodes (through
util) or text through
- Rich utility functions for syntax nodes through
The crate relies on a concept of untyped
SyntaxNodes vs typed
Syntax nodes represent the syntax tree in an untyped way. They represent a location in an immutable
tree with two pointers. The syntax tree is composed of
SyntaxTokens in a nested
tree structure. Each node can have parents, siblings, children, descendants, etc.
AstNodes represent a typed version of a syntax node. They have the same exact representation as syntax nodes
therefore a conversion between either has zero runtime cost. Every piece of data of an ast node is optional,
this is due to the fact that the parser is completely error tolerant.
Each representation has its advantages:
- Very simple traversing of the syntax tree through functions on them.
- Easily able to convert to underlying text, range, or tokens.
- Contain all whitespace bound to the underlying production (in the case of lossless parsing).
- Can be easily converted into its typed representation with zero cost.
- Can be turned into a pretty representation with fmt debug.
- Easy access to properties of the underlying production.
- Zero cost conversion to a syntax node.
In conclusion, the use of both representations means we are not constrained to acting through typed nodes. Which makes traversal hard and you often have to resort to autogenerated visitor patterns. AST nodes are simply a way to easily access subproperties of a syntax node.event;
pub use crate::ast::AstNode;
pub use crate::ast::AstToken;
pub use crate::util::SyntaxNodeExt;
pub use crate::util::SyntaxTokenExt;
AST definitions for converting untyped syntax nodes into typed AST nodes.
The Js syntax itself and parser functions.
Extra utlities for untyped syntax nodes, syntax tokens, and AST nodes.
Utility macro for creating a SyntaxKind through simple macro syntax
SyntaxNode against an
A simple macro for making assign, binop, or unary operators
Utility macro for making a new token set
A big signed integer type.
A structure signifying the Parser progress at one point in time
A structure signifying a completed node
Internal node in the immutable tree. It has other nodes and tokens as children.
Structure for converting events to a syntax tree representation, while preserving whitespace.
Structure to convert events to a lossy syntax tree which does not preserve whitespace.
A structure signifying the start of parsing of a syntax tree node
A utility struct for managing the result of a parser job
State kept by the parser while parsing. It is required for things such as strict mode or async functions
SmolStr is a string type that has the following properties:
A structure describing the syntax features the parser will accept. The default is an ECMAScript 2021 Script without any proposals.
A measure of text length. Also, equivalently, an index into text.
Abstracted token for
The source of tokens for the parser
Events emitted by the Parser, these events are later
made into a syntax tree with
process into TreeSink.
The kind of file we are parsing
The kind of syntax node, e.g.
WalkEvent describes tree walking process.
An abstraction for syntax tree implementations
Parse a js number as a string into a number.
parse_text but configures the parser to parse an ECMAScript module instead of a script
parse_text_lossy but configures the parser to parse an ECMAScript module instead of a Script
Generate the syntax tree with the control of events.
Run the rslint_lexer lexer to turn source code into tokens and errors produced by the lexer