Cargo Features

FieldMask has no features set by default.

[dependencies]
fieldmask = { version = "0.0.4", features = ["prost-integration"] }
prost-integration = prost

Enables prost of fieldmask_derive

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.

prost prost-integration?