Cargo Features

swc_ecma_transforms_react = { version = "0.183.19", default-features = false, features = ["concurrent", "serde-impl"] }
default = serde-impl

The serde-impl feature is set by default whenever swc_ecma_transforms_react is added without default-features = false somewhere in the dependency tree.

concurrent = rayon
serde-impl default = serde

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

rayon concurrent?
serde serde-impl