swc-project/swc · error · anyhow::Error

Syntax Error

Error message

Syntax Error

What it means

Thrown by swc-ast-explorer's parse_source (crates/swc-ast-explorer/src/parser.rs). The file is always parsed as TypeScript with TSX enabled; the error fires both for fatal parse errors and for recovered errors - by design, recovered diagnostics are treated as fatal so the CLI never prints a partial AST for invalid input. The actual diagnostic is emitted to the handler before bailing, so the message itself is intentionally generic.

Source

Thrown at crates/swc-ast-explorer/src/parser.rs:18

use anyhow::{anyhow, bail, Result};
use swc_common::{errors::Handler, SourceFile};
use swc_ecma_ast::{EsVersion, Program};
use swc_ecma_parser::{parse_file_as_program, Syntax, TsSyntax};

/// Parses a source file as JavaScript, TypeScript, or TSX and returns the SWC
/// program tree. Recovered parser errors are treated as fatal so the CLI does
/// not print partial ASTs for invalid input.
pub fn parse_source(file: &SourceFile, handler: &Handler) -> Result<Program> {
    let syntax = Syntax::Typescript(TsSyntax {
        tsx: true,
        ..Default::default()
    });
    let mut errors = Vec::new();
    let program = parse_file_as_program(file, syntax, EsVersion::latest(), None, &mut errors)
        .map_err(|err| {
            err.into_diagnostic(handler).emit();
            anyhow!("Syntax Error")
        })?;

    let mut has_recovered_error = false;
    for err in errors {
        err.into_diagnostic(handler).emit();
        has_recovered_error = true;
    }

    if has_recovered_error {
        bail!("Syntax Error");
    }

    Ok(program)
}

View on GitHub (pinned to d7d7434666)

Solutions

1. Look at the diagnostic printed above the error - it has the exact line/column - and fix the syntax at that spot
2. Verify the file parses elsewhere first (tsc --noEmit, or swc CLI with matching syntax) before exploring it
3. Update swc-ast-explorer so its parser supports the newest syntax used in the file
4. If the file relies on JS-only syntax the TS grammar misreads, preprocess or rename to an appropriate setup before exploring

Example fix

// before: ambiguous type-cast syntax breaks the TS grammar
const n = <number>value;

// after: use the as-form the TSX-capable grammar accepts
const n = value as number;

// Skip files that do not even tokenize/parse before exploring
// (cheap pre-check with the same parser family, e.g. run swc transform once)
import { transformSync } from '@swc/core';
function isParseable(filename, code) {
  try {
    transformSync(code, { filename, jsc: { parser: { syntax: 'typescript', tsx: true } } });
    return true;
  } catch {
    return false;
  }
}

// CLI context: check exit status and stderr
// $ swc-ast-explore file.ts 2>diag.txt || handle 'Syntax Error'
// Library context (Rust):
// let program = parse_source(&fm, &handler).unwrap_or_else(|e| {
//     eprintln!("explorer cannot parse this file: {e}");
//     std::process::exit(1);
// });

When it happens

Trigger: Running the swc-ast-explorer CLI on a file with any syntax error; feeding TSX/JSX into a context where the TS+TSX grammar still rejects it (e.g. ambiguous '<Type>expr' casts in .ts-mode content, invalid decorators, unfinished template literals); exploring files with proposal syntax the vendored parser version does not support.

Common situations: Pointing the explorer at draft or WIP files that do not compile; using an older explorer build against newer language syntax; files that are valid JS but rejected by the stricter TS grammar used unconditionally here.

Related errors

• Failed to parse the input
• Syntax Error
• Bundle command is not yet implemented
• Lint command is not yet implemented
• Minify command is not yet implemented

AI-assisted analysis of swc-project/swc@d7d7434666 (2026-08-16). Data as JSON: /api/errors/8db5a284b1c33797. Report an issue: GitHub.