knut-thund 0.1.5

//! Error types for the Þund engine.

use thiserror::Error;

/// Result alias for the crate.
pub type Result<T> = std::result::Result<T, ThundError>;

/// Anything that can go wrong building, lowering, or running a pipeline.
#[derive(Debug, Error)]
pub enum ThundError {
    /// Two datasets or two flows share a name.
    #[error("duplicate {kind} name: {name}")]
    DuplicateName {
        /// `"dataset"` or `"flow"`.
        kind: &'static str,
        /// The offending name.
        name: String,
    },

    /// A flow writes to a target that is not a declared dataset.
    #[error("flow {flow} writes to undefined dataset {target}")]
    DanglingFlow {
        /// The offending flow.
        flow: String,
        /// The missing target.
        target: String,
    },

    /// The in-graph dataflow contains a cycle.
    #[error("pipeline dataflow graph is cyclic")]
    Cyclic,

    /// A backend was asked to do something it does not support (e.g. the
    /// Spark backend asked to run an output mode SDP cannot express).
    #[error("backend `{backend}` does not support: {what}")]
    Unsupported {
        /// Backend name.
        backend: &'static str,
        /// What was unsupported.
        what: String,
    },

    /// The DSL text could not be parsed into a [`crate::ir::Pipeline`].
    #[error("dsl parse error: {0}")]
    Dsl(String),

    /// The SQL text could not be parsed into a [`crate::ir::Pipeline`]
    /// (see [`crate::authoring::sql`], feature `sql`).
    #[error("sql parse error: {0}")]
    Sql(String),

    /// A backend runtime failure (connection, execution, …).
    #[error("backend error: {0}")]
    Backend(String),
}