schemars/docs/4-features.md

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default	Feature Flags	5	/features/

Feature Flags and Optional Dependencies

• derive (enabled by default) - provides #[derive(JsonSchema)] macro
• impl_json_schema - implements JsonSchema for Schemars types themselves
• preserve_order - keep the order of struct fields in Schema and SchemaObject

Schemars can implement JsonSchema on types from several popular crates, enabled via feature flags (dependency versions are shown in brackets):

• chrono - chrono (^0.4)
• indexmap1 - indexmap (^1.2)
• indexmap2 - indexmap (^2.0)
• either - either (^1.3)
• uuid08 - uuid (^0.8)
• uuid1 - uuid (^1.0)
• smallvec - smallvec (^1.0)
• arrayvec05 - arrayvec (^0.5)
• arrayvec07 - arrayvec (^0.7)
• url - url (^2.0)
• bytes - bytes (^1.0)
• enumset - enumset (^1.0)
• rust_decimal - rust_decimal (^1.0)
• bigdecimal - bigdecimal (^0.3)
• smol_str - smol_str (^0.1.17)
• semver - semver (^1.0.9)

For example, to implement JsonSchema on types from chrono, enable it as a feature in the schemars dependency in your Cargo.toml like so:

[dependencies]
schemars = { version = "0.8", features = ["chrono"] }