EcmaScript/TypeScript parser for the rust programming language.

Features

Heavily tested

Passes almost all tests from tc39/test262.

Error reporting

error: 'implements', 'interface', 'let', 'package', 'private', 'protected',  'public', 'static', or 'yield' cannot be used as an identifier in strict mode
 --> invalid.js:3:10
  |
3 | function yield() {
  |          ^^^^^

Error recovery

The parser can recover from some parsing errors. For example, parser returns Ok(Module) for the code below, while emitting error to handler.

const CONST = 9000 % 2;
const enum D {
    // Comma is required, but parser can recover because of the newline.
    d = 10
    g = CONST
}

Example (lexer)

See lexer.rs in examples directory.

Example (parser)

#[macro_use]
extern crate swc_common;
extern crate swc_ecma_parser;
use swc_common::sync::Lrc;
use swc_common::{
    errors::{ColorConfig, Handler},
    FileName, FilePathMapping, SourceMap,
};
use swc_ecma_parser::{lexer::Lexer, Parser, StringInput, Syntax};

fn main() {
    let cm: Lrc<SourceMap> = Default::default();
    let handler =
        Handler::with_tty_emitter(ColorConfig::Auto, true, false,
        Some(cm.clone()));

    // Real usage
    // let fm = cm
    //     .load_file(Path::new("test.js"))
    //     .expect("failed to load test.js");
    let fm = cm.new_source_file(
        FileName::Custom("test.js".into()).into(),
        "function foo() {}",
    );
    let lexer = Lexer::new(
        // We want to parse ecmascript
        Syntax::Es(Default::default()),
        // EsVersion defaults to es5
        Default::default(),
        StringInput::from(&*fm),
        None,
    );

    let mut parser = Parser::new_from(lexer);

    for e in parser.take_errors() {
        e.into_diagnostic(&handler).emit();
    }

    let _module = parser
        .parse_module()
        .map_err(|mut e| {
            // Unrecoverable fatal error occurred
            e.into_diagnostic(&handler).emit()
        })
        .expect("failed to parser module");
}

Example (flow parser)

# #[cfg(feature = "flow")] {
use swc_common::{sync::Lrc, FileName, SourceMap};
use swc_ecma_ast::EsVersion;
use swc_ecma_parser::{parse_file_as_program, FlowSyntax, Syntax};

let cm: Lrc<SourceMap> = Default::default();
let fm = cm.new_source_file(
    FileName::Custom("test.js".into()).into(),
    "// @flow\nconst value: number = 1;",
);
let mut recovered_errors = Vec::new();

let program = parse_file_as_program(
    &fm,
    Syntax::Flow(FlowSyntax {
        require_directive: true,
        ..Default::default()
    }),
    EsVersion::latest(),
    None,
    &mut recovered_errors,
)
.expect("flow should parse");

assert!(recovered_errors.is_empty());
let _ = program;
# }

Cargo features

`typescript`

Enables typescript parser.

`flow`

Enables flow parser. This feature requires typescript.

`verify`

Verify more errors, using swc_ecma_visit.

Known issues

Null character after `\`

Because [String] of rust should only contain valid utf-8 characters while javascript allows non-utf8 characters, the parser stores invalid utf8 characters in escaped form.

As a result, swc needs a way to distinguish invalid-utf8 code points and input specified by the user. The parser stores a null character right after \\ for non-utf8 code points. Note that other parts of swc is aware of this fact.

Note that this can be changed at anytime with a breaking change.

swc_ecma_parser 39.0.0