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#42 in Parser implementations

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61,544 downloads per month
Used in 122 crates (52 directly)

Apache-2.0

1.5MB
34K SLoC

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()),
        "function foo() {}".into(),
    );
    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");
}

Cargo features

typescript

Enables typescript parser.

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.

Dependencies

~6–11MB
~223K SLoC