feat: dagrunner, initial version

src/error.rs

@@ -0,0 +1,94 @@
+//! Error types for DAG operations.
+//!
+//! This module defines the error types that can occur during DAG construction and execution.
+
+/// Errors that can occur during DAG construction and execution
+#[derive(Debug, Clone, PartialEq)]
+pub enum DagError {
+    /// A cycle was detected in the DAG
+    CycleDetected {
+        nodes: Vec<usize>,
+        description: String,
+    },
+    /// Invalid dependency: task does not exist
+    InvalidDependency { task_id: usize },
+    /// Type mismatch in task dependencies
+    TypeMismatch {
+        expected: &'static str,
+        found: &'static str,
+    },
+    /// Task panicked during execution
+    TaskPanicked {
+        task_id: usize,
+        panic_message: String,
+    },
+    /// Result not found for task
+    ResultNotFound { task_id: usize },
+}
+
+impl std::fmt::Display for DagError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            DagError::CycleDetected { nodes, description } => {
+                write!(
+                    f,
+                    "Cycle detected in DAG: {}\n\
+                     Nodes involved: {:?}\n\
+                     \n\
+                     A DAG cannot have cycles. Review your dependency graph to identify \
+                     and remove circular dependencies.",
+                    description, nodes
+                )
+            }
+            DagError::InvalidDependency { task_id } => {
+                write!(
+                    f,
+                    "Invalid dependency: task #{} does not exist.\n\
+                     \n\
+                     Ensure all task handles reference tasks that have been added to the DAG.",
+                    task_id
+                )
+            }
+            DagError::TypeMismatch { expected, found } => {
+                write!(
+                    f,
+                    "Type mismatch in task dependencies.\n\
+                     Expected: {}\n\
+                     Found: {}\n\
+                     \n\
+                     Verify that dependency types match the task's Input type exactly.",
+                    expected, found
+                )
+            }
+            DagError::TaskPanicked {
+                task_id,
+                panic_message,
+            } => {
+                write!(
+                    f,
+                    "Task #{} panicked during execution: {}\n\
+                     \n\
+                     A task panicked, indicating a bug. The entire DAG execution is aborted.",
+                    task_id, panic_message
+                )
+            }
+            DagError::ResultNotFound { task_id } => {
+                write!(
+                    f,
+                    "Result not found for task #{}.\n\
+                     \n\
+                     Call dag.run() before accessing results with get().",
+                    task_id
+                )
+            }
+        }
+    }
+}
+
+impl std::error::Error for DagError {}
+
+/// Result type for DAG operations
+pub type DagResult<T> = Result<T, DagError>;
+
+#[cfg(test)]
+mod tests;