swc-project/swc · error

swc does not support ObjectPropVal::Pattern({pat:?})

Error message

swc does not support ObjectPropVal::Pattern({pat:?})

What it means

Raised in `Swcify for ObjectProperty` (swcify/expr.rs:533). Babel allows an object property whose value is a Pattern (shorthand/assignment-pattern forms) other than a simple identifier, e.g. `{a = 1} = ...` style defaults or computed destructuring. The code only rewrites PatternLike::Id into a key-value prop; any other pattern shape (AssignmentPattern, RestElement, ObjectPattern, ArrayPattern) has no swc KeyValueProp representation, so it panics. The pattern value that is not a plain identifier is the input at fault.

Source

Thrown at crates/swc_estree_compat/src/swcify/expr.rs:533

                    span: expr.span(),
                    expr,
                })
            }
        }
    }
}

impl Swcify for ObjectProperty {
    type Output = KeyValueProp;

    fn swcify(self, ctx: &Context) -> Self::Output {
        KeyValueProp {
            key: self.key.swcify(ctx),
            value: match self.value {
                ObjectPropVal::Pattern(pat) => match pat {
                    PatternLike::Id(i) => i.swcify(ctx).into(),
                    _ => {
                        panic!("swc does not support ObjectPropVal::Pattern({pat:?})")
                    }
                },
                ObjectPropVal::Expr(e) => e.swcify(ctx),
            },
        }
    }
}

impl Swcify for SequenceExpression {
    type Output = SeqExpr;

    fn swcify(self, ctx: &Context) -> Self::Output {
        SeqExpr {
            span: ctx.span(&self.base),
            exprs: self.expressions.swcify(ctx),
        }
    }
}

View on GitHub (pinned to 5176682b65)

Solutions

1. Before swcifying, verify each ObjectProperty with a Pattern value only wraps a plain Identifier; reject others with a descriptive error
2. Extend the conversion to desugar non-identifier shorthand patterns (e.g. assignment defaults) into equivalent swc nodes if the semantics are representable
3. Handle the Babel AST stage that produces these pattern-valued properties earlier, so they never reach this conversion

When it happens

Trigger: Thrown at crates/swc_estree_compat/src/swcify/expr.rs:533 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/d1f416cb2577d59b. Report an issue: GitHub.