swc-project/swc · error

Unsupported meta: {:#?}

Error message

Unsupported meta: {:#?}

What it means

Compile-time panic from `#[derive(StringEnum)]` (crates/string_enum). The optional per-variant `#[string_enum(...)]` attribute is only supported in list form — `#[string_enum(alias("foo"))]` adds extra FromStr match arms. If the attribute appears as a bare path (`#[string_enum]`) or name-value form, `attr.meta` is not `Meta::List` and the macro panics with `Unsupported meta: {:#?}`.

Source

Thrown at crates/string_enum/src/lib.rs:160

                    for item in parse2::<FieldAttr>(meta.tokens.clone())
                        .expect("failed to parse `#[string_enum]`")
                        .aliases
                    {
                        cases.push(Pat::Lit(PatLit {
                            attrs: Default::default(),
                            lit: Lit::Str(item.alias),
                        }));
                    }

                    pat = Pat::Or(PatOr {
                        attrs: Default::default(),
                        leading_vert: None,
                        cases,
                    });
                    continue;
                }

                panic!("Unsupported meta: {:#?}", attr.meta);
            }

            let body = match *v.data() {
                Fields::Unit => Box::new(parse_quote!(return Ok(#qual_name))),
                _ => unreachable!("StringEnum requires all variants not to have fields"),
            };

            Arm {
                body,
                attrs: v
                    .attrs()
                    .iter()
                    .filter(|attr| is_attr_name(attr, "cfg"))
                    .cloned()
                    .collect(),
                pat,
                guard: None,
                fat_arrow_token: Default::default(),

View on GitHub (pinned to 5176682b65)

Solutions

1. Use the list form: `#[string_enum(alias("foo"))]`
2. Remove the attribute entirely if no alias is needed

Example fix

// before
#[string_enum(alias = "commonjs")]
CommonJs,

// after
#[string_enum(alias("commonjs"))]
CommonJs,

When it happens

Trigger: Writing `#[string_enum]` alone or `#[string_enum(alias = "foo")]` on a variant of a StringEnum-deriving enum.

Common situations: Trying to add alias support and guessing the syntax; attribute style drift after refactors.

Related errors

• StringEnum: Cannot determine string value of this variant
• An element descriptor's .kind property must be either "metho
• An element descriptor's .placement property must be one of "
• A class descriptor's .kind property must be "class", but a d
• ${objectType} can't have a .${name} property.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/1b0a19f8c820a38b. Report an issue: GitHub.