swc-project/swc · error

module item found but is_es6 is false: {:?}

Error message

module item found but is_es6 is false: {:?}

What it means

A consistency check panic while building the CommonJS wrapper function in the bundler's chunk output (cjs.rs:142). The generated wrapper's body is assembled from module items; the invariant is that items are only emitted into the CJS interop wrapper when the module is treated as ES6 (is_es6). If a module item is present but the is_es6 flag is false, module classification and item collection have diverged, and the panic fires to expose that internal inconsistency.

Source

Thrown at crates/swc_bundler/src/bundler/chunk/cjs.rs:142

                    pat: Pat::Ident(Ident::new(atom!("module"), DUMMY_SP, local_ctxt).into()),
                },
                // exports
                Param {
                    span: DUMMY_SP,
                    decorators: Default::default(),
                    pat: Pat::Ident(Ident::new(atom!("exports"), DUMMY_SP, local_ctxt).into()),
                },
            ],
            decorators: Vec::new(),
            span: DUMMY_SP,
            body: Some(FunctionBody {
                span: dep.span,
                stmts: dep
                    .body
                    .into_iter()
                    .map(|v| match v {
                        ModuleItem::ModuleDecl(i) => {
                            unreachable!("module item found but is_es6 is false: {:?}", i)
                        }
                        ModuleItem::Stmt(s) => s,
                        #[cfg(swc_ast_unknown)]
                        _ => panic!("unable to access unknown nodes"),
                    })
                    .collect(),
            }),
            is_generator: false,
            is_async: false,
            ..Default::default()
        }),
    }
    .into();

    // var load = __swcpack_require__.bind(void 0, moduleDecl)

    VarDecl {
        span: DUMMY_SP,

View on GitHub (pinned to 5176682b65)

Solutions

1. Log the offending module item and its module id to find which module was misclassified
2. Ensure the module graph classification pass (which sets is_es6) runs before chunk item collection and uses the same criteria
3. Skip non-ES6 items in the CJS wrapper construction instead of panicking if the item is genuinely irrelevant

When it happens

Trigger: Thrown at crates/swc_bundler/src/bundler/chunk/cjs.rs:142 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/b94201859c47d6f1. Report an issue: GitHub.