CEL evaluation

parcel_runtime::reference evaluates CEL expressions and converts caller, dataset, and Arrow values. Most applications can use the higher-level caller and validation functions.

Scope

Field	Type	Meaning
ctx	Option<cel::Value>	Caller namespace, when needed.
dataset	Option<cel::Value>	Dataset namespace, when needed.
row	Option<cel::Value>	Row namespace; absent keys represent null values.
pins	BTreeSet<FunctionPin>	Exact custom function implementations the expression can call.

Scope::default() has no namespace values and an empty pin set.

Context and evaluation

pub fn context(scope: &Scope) -> cel::Context<'static>;
pub fn eval(src: &str, ctx: &cel::Context) -> Result<cel::Value, String>;
pub fn eval_bool(src: &str, ctx: &cel::Context) -> Result<bool, String>;

context registers the standard library, parcel functions, and the supplied namespaces. src is CEL expression text. Evaluation returns a value or an error string; eval_bool also rejects results that are not Boolean.

use parcel_runtime::{Caller, reference::{self, Scope}};

let caller = Caller::new("analyst", "globex", "purchasing");
let scope = Scope {
    ctx: Some(reference::ctx_value(&caller)),
    ..Scope::default()
};
let context = reference::context(&scope);
assert_eq!(reference::eval_bool("ctx.tenant == 'globex'", &context), Ok(true));

Value conversion

Signatures below use Value for cel::Value and Type for parcel_core::types::Type.

Signature	Parameters and result
ctx_value(c: &Caller) -> Value	Converts standard caller fields into a CEL namespace.
ctx_value_typed(c: &Caller, declared: &BTreeMap<String, Type>) -> Value	Also converts declared custom caller fields according to their types.
json_value(j: &serde_json::Value, ty: &Type) -> Option<Value>	Converts JSON to the requested CEL type; returns None when incompatible.
dataset_value(entries: &[(String, Value)]) -> Value	Builds nested dataset values from dotted field paths and values.
string(s: &str) -> Value	Creates a CEL string.
timestamp(t: DateTime<Utc>) -> Value	Creates a CEL timestamp.
to_scalar(v: &Value, ty: &Type) -> Result<ScalarValue, String>	Converts a CEL value to a typed DataFusion scalar, or returns an error.
from_scalar(s: &ScalarValue) -> Option<Value>	Converts a supported non-null scalar to CEL; otherwise returns None.
list_type(elem: &Type) -> DataType	Creates the Arrow list type for the element type.
timestamp_type() -> DataType	Returns the Arrow timestamp type used by the interpreter.