Serde serializer for generating syntactically valid Starlark, the declarative format used for describing build targets in build systems including Bazel, Buck, Pants, and Please.

The following example serializes a minimal Bazel target for the syn crate.

The tests/bazel.rs test in this repo has a somewhat more fleshed out example of this use case, including things like load(…), package(default_visibility = …), distinct include and exclude arguments to glob(…), and select({…}).

#[derive(Serialize)]
#[serde(rename = "rust_library")]
pub struct RustLibrary {
    pub name: String,
    pub srcs: Glob,
    pub crate_features: BTreeSet<String>,
    pub edition: u16,
    pub deps: BTreeSet<String>,
}

#[derive(Serialize)]
#[serde(rename = "glob")]
pub struct Glob(pub BTreeSet<String>);

fn main() {
    let rust_library = RustLibrary { ... };

    print!("{}", serde_starlark::to_string(&rust_library).unwrap());
}

rust_library(
    name = "syn",
    srcs = glob(["**/*.rs"]),
    crate_features = [
        "default",
        "full",
    ],
    edition = 2018,
    deps = [
        ":proc-macro2",
        ":quote",
        ":unicode-ident",
    ],
)

The primitive types (integers, boolean, string) serialize in the obvious way to Starlark.

Serde sequences serialize to Starlark arrays. Serde maps serialize to Starlark maps.

Rust structs with named fields serialize to Starlark "function calls" with named arguments:

#[derive(Serialize)]
#[serde(rename = "rust_library")]
pub struct RustLibrary {
    pub name: String,
    pub edition: u16,
}

rust_library(
    name = "syn",
    edition = 2018,
)

Rust newtype structs and tuple structs serialize to Starlark "function calls" with positional arguments:

#[derive(Serialize)]
#[serde(rename = "select")]
pub struct Select<T>(pub BTreeMap<String, T>);

select({
    "//conditions:default": [],
})

To make a newtype struct which does not appear as a function call, use the serde(transparent) attribute.

#[derive(Serialize)]
#[serde(transparent)]
pub struct Dependency(pub String);

Fields of type Option<T> serialize as either None or the value if present. Consider using serde(skip_serializing_if = "Option::is_none") to omit fields with value None from the serialized output.