cu29_traits/

lib.rs

//! Common copper traits and types for robotics systems.
//!
//! This crate is no_std compatible by default. Enable the "std" feature for additional
//! functionality like implementing `std::error::Error` for `CuError` and the
//! `new_with_cause` method that accepts types implementing `std::error::Error`.
//!
//! # Features
//!
//! - `std` (default): Enables standard library support
//!   - Implements `std::error::Error` for `CuError`
//!   - Adds `CuError::new_with_cause()` method for interop with std error types
//!
//! # no_std Usage
//!
//! To use without the standard library:
//!
//! ```toml
//! [dependencies]
//! cu29-traits = { version = "0.9", default-features = false }
//! ```

#![cfg_attr(not(feature = "std"), no_std)]
extern crate alloc;

#[cfg(feature = "reflect")]
pub use bevy_reflect::Reflect;
use bincode::de::{BorrowDecoder, Decoder};
use bincode::enc::Encoder;
use bincode::enc::write::Writer;
use bincode::error::{DecodeError, EncodeError};
use bincode::{BorrowDecode, Decode as dDecode, Decode, Encode, Encode as dEncode};
use compact_str::CompactString;
use cu29_clock::{PartialCuTimeRange, Tov};
use serde::de::{self, SeqAccess, Visitor};
use serde::{Deserialize, Deserializer, Serialize};

use alloc::borrow::ToOwned;
use alloc::boxed::Box;
use alloc::format;
use alloc::string::{String, ToString};
use alloc::vec::Vec;
#[cfg(feature = "std")]
use core::cell::Cell;
#[cfg(not(feature = "std"))]
use core::error::Error as CoreError;
use core::fmt::{Debug, Display, Formatter};
#[cfg(feature = "std")]
use std::error::Error;

#[cfg(not(feature = "std"))]
use spin::Mutex as SpinMutex;

// Type alias for the boxed error type to simplify conditional compilation
#[cfg(feature = "std")]
type DynError = dyn std::error::Error + Send + Sync + 'static;
#[cfg(not(feature = "std"))]
type DynError = dyn core::error::Error + Send + Sync + 'static;

/// A simple wrapper around String that implements Error trait.
/// Used for cloning and deserializing CuError causes.
#[derive(Debug)]
struct StringError(String);

impl Display for StringError {
    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
        write!(f, "{}", self.0)
    }
}

#[cfg(feature = "std")]
impl std::error::Error for StringError {}

#[cfg(not(feature = "std"))]
impl core::error::Error for StringError {}

/// Common copper Error type.
///
/// This error type stores an optional cause as a boxed dynamic error,
/// allowing for proper error chaining while maintaining Clone and
/// Serialize/Deserialize support through custom implementations.
pub struct CuError {
    message: String,
    cause: Option<Box<DynError>>,
}

// Custom Debug implementation that formats cause as string
impl Debug for CuError {
    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("CuError")
            .field("message", &self.message)
            .field("cause", &self.cause.as_ref().map(|e| e.to_string()))
            .finish()
    }
}

// Custom Clone implementation - clones cause as StringError wrapper
impl Clone for CuError {
    fn clone(&self) -> Self {
        CuError {
            message: self.message.clone(),
            cause: self
                .cause
                .as_ref()
                .map(|e| Box::new(StringError(e.to_string())) as Box<DynError>),
        }
    }
}

// Custom Serialize - serializes cause as Option<String>
impl Serialize for CuError {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        use serde::ser::SerializeStruct;
        let mut state = serializer.serialize_struct("CuError", 2)?;
        state.serialize_field("message", &self.message)?;
        state.serialize_field("cause", &self.cause.as_ref().map(|e| e.to_string()))?;
        state.end()
    }
}

// Custom Deserialize - deserializes cause as StringError wrapper
impl<'de> Deserialize<'de> for CuError {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        #[derive(Deserialize)]
        struct CuErrorHelper {
            message: String,
            cause: Option<String>,
        }

        let helper = CuErrorHelper::deserialize(deserializer)?;
        Ok(CuError {
            message: helper.message,
            cause: helper
                .cause
                .map(|s| Box::new(StringError(s)) as Box<DynError>),
        })
    }
}

impl Display for CuError {
    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
        let context_str = match &self.cause {
            Some(c) => c.to_string(),
            None => "None".to_string(),
        };
        write!(f, "{}\n   context:{}", self.message, context_str)?;
        Ok(())
    }
}

#[cfg(not(feature = "std"))]
impl CoreError for CuError {
    fn source(&self) -> Option<&(dyn CoreError + 'static)> {
        self.cause
            .as_deref()
            .map(|e| e as &(dyn CoreError + 'static))
    }
}

#[cfg(feature = "std")]
impl Error for CuError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        self.cause.as_deref().map(|e| e as &(dyn Error + 'static))
    }
}

impl From<&str> for CuError {
    fn from(s: &str) -> CuError {
        CuError {
            message: s.to_string(),
            cause: None,
        }
    }
}

impl From<String> for CuError {
    fn from(s: String) -> CuError {
        CuError {
            message: s,
            cause: None,
        }
    }
}

impl CuError {
    /// Creates a new CuError from an interned string index.
    /// Used by the cu_error! macro.
    ///
    /// The index is stored as a placeholder string `[interned:{index}]`.
    /// Actual string resolution happens at logging time via the unified logger.
    pub fn new(message_index: usize) -> CuError {
        CuError {
            message: format!("[interned:{}]", message_index),
            cause: None,
        }
    }

    /// Creates a new CuError with a message and an underlying cause.
    ///
    /// # Example
    /// ```
    /// use cu29_traits::CuError;
    ///
    /// let io_err = std::io::Error::other("io error");
    /// let err = CuError::new_with_cause("Failed to read file", io_err);
    /// ```
    #[cfg(feature = "std")]
    pub fn new_with_cause<E>(message: &str, cause: E) -> CuError
    where
        E: std::error::Error + Send + Sync + 'static,
    {
        CuError {
            message: message.to_string(),
            cause: Some(Box::new(cause)),
        }
    }

    /// Creates a new CuError with a message and an underlying cause.
    #[cfg(not(feature = "std"))]
    pub fn new_with_cause<E>(message: &str, cause: E) -> CuError
    where
        E: core::error::Error + Send + Sync + 'static,
    {
        CuError {
            message: message.to_string(),
            cause: Some(Box::new(cause)),
        }
    }

    /// Adds or replaces the cause with a context string.
    ///
    /// This is useful for adding context to errors during propagation.
    ///
    /// # Example
    /// ```
    /// use cu29_traits::CuError;
    ///
    /// let err = CuError::from("base error").add_cause("additional context");
    /// ```
    pub fn add_cause(mut self, context: &str) -> CuError {
        self.cause = Some(Box::new(StringError(context.to_string())));
        self
    }

    /// Adds a cause error to this CuError (builder pattern).
    ///
    /// # Example
    /// ```
    /// use cu29_traits::CuError;
    ///
    /// let io_err = std::io::Error::other("io error");
    /// let err = CuError::from("Operation failed").with_cause(io_err);
    /// ```
    #[cfg(feature = "std")]
    pub fn with_cause<E>(mut self, cause: E) -> CuError
    where
        E: std::error::Error + Send + Sync + 'static,
    {
        self.cause = Some(Box::new(cause));
        self
    }

    /// Adds a cause error to this CuError (builder pattern).
    #[cfg(not(feature = "std"))]
    pub fn with_cause<E>(mut self, cause: E) -> CuError
    where
        E: core::error::Error + Send + Sync + 'static,
    {
        self.cause = Some(Box::new(cause));
        self
    }

    /// Returns a reference to the underlying cause, if any.
    pub fn cause(&self) -> Option<&(dyn core::error::Error + Send + Sync + 'static)> {
        self.cause.as_deref()
    }

    /// Returns the error message.
    pub fn message(&self) -> &str {
        &self.message
    }
}

/// Creates a CuError with a message and cause in a single call.
///
/// This is a convenience function for use with `.map_err()`.
///
/// # Example
/// ```
/// use cu29_traits::with_cause;
///
/// let result: Result<(), std::io::Error> = Err(std::io::Error::other("io error"));
/// let cu_result = result.map_err(|e| with_cause("Failed to read file", e));
/// ```
#[cfg(feature = "std")]
pub fn with_cause<E>(message: &str, cause: E) -> CuError
where
    E: std::error::Error + Send + Sync + 'static,
{
    CuError::new_with_cause(message, cause)
}

/// Creates a CuError with a message and cause in a single call.
#[cfg(not(feature = "std"))]
pub fn with_cause<E>(message: &str, cause: E) -> CuError
where
    E: core::error::Error + Send + Sync + 'static,
{
    CuError::new_with_cause(message, cause)
}

// Generic Result type for copper.
pub type CuResult<T> = Result<T, CuError>;

#[cfg(feature = "std")]
thread_local! {
    static OBSERVED_ENCODE_BYTES: Cell<Option<usize>> = const { Cell::new(None) };
}

#[cfg(not(feature = "std"))]
static OBSERVED_ENCODE_BYTES: SpinMutex<Option<usize>> = SpinMutex::new(None);

/// Starts observed byte counting for the current encode pass.
pub fn begin_observed_encode() {
    #[cfg(feature = "std")]
    OBSERVED_ENCODE_BYTES.with(|bytes| {
        debug_assert!(
            bytes.get().is_none(),
            "observed encode measurement must not be nested"
        );
        bytes.set(Some(0));
    });

    #[cfg(not(feature = "std"))]
    {
        let mut bytes = OBSERVED_ENCODE_BYTES.lock();
        debug_assert!(
            bytes.is_none(),
            "observed encode measurement must not be nested"
        );
        *bytes = Some(0);
    }
}

/// Ends observed byte counting and returns the total bytes written.
pub fn finish_observed_encode() -> usize {
    #[cfg(feature = "std")]
    {
        OBSERVED_ENCODE_BYTES.with(|bytes| bytes.replace(None).unwrap_or(0))
    }

    #[cfg(not(feature = "std"))]
    {
        OBSERVED_ENCODE_BYTES.lock().take().unwrap_or(0)
    }
}

/// Aborts any active observed byte counting session.
pub fn abort_observed_encode() {
    #[cfg(feature = "std")]
    OBSERVED_ENCODE_BYTES.with(|bytes| bytes.set(None));

    #[cfg(not(feature = "std"))]
    {
        *OBSERVED_ENCODE_BYTES.lock() = None;
    }
}

/// Returns the number of bytes written so far in the current observed encode pass.
pub fn observed_encode_bytes() -> usize {
    #[cfg(feature = "std")]
    {
        OBSERVED_ENCODE_BYTES.with(|bytes| bytes.get().unwrap_or(0))
    }

    #[cfg(not(feature = "std"))]
    {
        OBSERVED_ENCODE_BYTES.lock().as_ref().copied().unwrap_or(0)
    }
}

/// Records bytes written by an observed writer.
pub fn record_observed_encode_bytes(bytes: usize) {
    #[cfg(feature = "std")]
    OBSERVED_ENCODE_BYTES.with(|total| {
        if let Some(current) = total.get() {
            total.set(Some(current.saturating_add(bytes)));
        }
    });

    #[cfg(not(feature = "std"))]
    {
        let mut total = OBSERVED_ENCODE_BYTES.lock();
        if let Some(current) = *total {
            *total = Some(current.saturating_add(bytes));
        }
    }
}

/// A bincode writer wrapper that reports every encoded byte to Copper's
/// observation counters.
pub struct ObservedWriter<W> {
    inner: W,
}

impl<W> ObservedWriter<W> {
    pub const fn new(inner: W) -> Self {
        Self { inner }
    }

    pub fn into_inner(self) -> W {
        self.inner
    }

    pub fn inner(&self) -> &W {
        &self.inner
    }

    pub fn inner_mut(&mut self) -> &mut W {
        &mut self.inner
    }
}

impl<W: Writer> Writer for ObservedWriter<W> {
    #[inline(always)]
    fn write(&mut self, bytes: &[u8]) -> Result<(), EncodeError> {
        self.inner.write(bytes)?;
        record_observed_encode_bytes(bytes.len());
        Ok(())
    }
}

/// Defines a basic write, append only stream trait to be able to log or send serializable objects.
pub trait WriteStream<E: Encode>: Debug + Send + Sync {
    fn log(&mut self, obj: &E) -> CuResult<()>;
    fn flush(&mut self) -> CuResult<()> {
        Ok(())
    }
    /// Optional byte count of the last successful `log` call, if the implementation can report it.
    fn last_log_bytes(&self) -> Option<usize> {
        None
    }
}

/// Defines the types of what can be logged in the unified logger.
#[derive(dEncode, dDecode, Copy, Clone, Debug, PartialEq)]
pub enum UnifiedLogType {
    Empty,             // Dummy default used as a debug marker
    StructuredLogLine, // This is for the structured logs (ie. debug! etc..)
    CopperList,        // This is the actual data log storing activities between tasks.
    FrozenTasks,       // Log of all frozen state of the tasks.
    LastEntry,         // This is a special entry that is used to signal the end of the log.
    RuntimeLifecycle,  // Runtime lifecycle events (mission/config/stack context).
}
/// Represent the minimum set of traits to be usable as Metadata in Copper.
pub trait Metadata: Default + Debug + Clone + Encode + Decode<()> + Serialize {}

impl Metadata for () {}

/// Origin metadata captured when a Copper-aware transport receives a remote message.
#[derive(Clone, Debug, PartialEq, Eq, Encode, Decode, Serialize, Deserialize)]
#[cfg_attr(feature = "reflect", derive(Reflect))]
pub struct CuMsgOrigin {
    pub subsystem_code: u16,
    pub instance_id: u32,
    pub cl_id: u64,
}

/// Key metadata piece attached to every message in Copper.
pub trait CuMsgMetadataTrait {
    /// The time range used for the processing of this message
    fn process_time(&self) -> PartialCuTimeRange;

    /// Small status text for user UI to get the realtime state of task (max 24 chrs)
    fn status_txt(&self) -> &CuCompactString;

    /// Remote Copper provenance captured on receive.
    fn origin(&self) -> Option<&CuMsgOrigin> {
        None
    }
}

/// A generic trait to expose the generated CuStampedDataSet from the task graph.
pub trait ErasedCuStampedData {
    fn payload(&self) -> Option<&dyn erased_serde::Serialize>;
    #[cfg(feature = "reflect")]
    fn payload_reflect(&self) -> Option<&dyn Reflect>;
    fn tov(&self) -> Tov;
    fn metadata(&self) -> &dyn CuMsgMetadataTrait;
}

/// Trait to get a vector of type-erased CuStampedDataSet
/// This is used for generic serialization of the copperlists
pub trait ErasedCuStampedDataSet {
    fn cumsgs(&self) -> Vec<&dyn ErasedCuStampedData>;
}

/// Provides per-output raw payload sizes aligned with `ErasedCuStampedDataSet::cumsgs` order.
pub trait CuPayloadRawBytes {
    /// Returns raw payload sizes (stack + heap) for each output message.
    /// `None` indicates the payload was not produced for that output.
    fn payload_raw_bytes(&self) -> Vec<Option<u64>>;
}

/// Trait to trace back from the CopperList the origin of each message slot.
///
/// The returned slice must be aligned with `ErasedCuStampedDataSet::cumsgs()`:
/// index `i` maps to copperlist slot `i`.
#[derive(Debug, Clone, Copy)]
pub struct TaskOutputSpec {
    pub task_id: &'static str,
    pub msg_type: &'static str,
    pub payload_type_path_fn: fn() -> &'static str,
}

impl TaskOutputSpec {
    #[inline]
    pub fn payload_type_path(&self) -> &'static str {
        (self.payload_type_path_fn)()
    }
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub enum DebugFieldSemantics {
    Time,
    OptionalTime,
    Duration,
    GeodeticPosition,
    Quantity {
        quantity_name: String,
        unit_symbol: String,
    },
}

#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "snake_case")]
pub enum DebugFieldKind {
    Scalar,
    Struct,
    TupleStruct,
    Tuple,
    List,
    Array,
    Map,
    Set,
    Enum,
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct DebugFieldDescriptor {
    pub display_path: String,
    #[serde(
        default,
        skip_serializing_if = "Option::is_none",
        deserialize_with = "deserialize_debug_binding_name"
    )]
    pub binding_name: Option<String>,
    pub field_type: String,
    pub value_type_path: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub semantics: Option<DebugFieldSemantics>,
    pub nullable: bool,
    pub kind: DebugFieldKind,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub children: Vec<DebugFieldDescriptor>,
}

fn deserialize_debug_binding_name<'de, D>(deserializer: D) -> Result<Option<String>, D::Error>
where
    D: Deserializer<'de>,
{
    struct BindingNameVisitor;

    impl<'de> Visitor<'de> for BindingNameVisitor {
        type Value = Option<String>;

        fn expecting(&self, formatter: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            formatter.write_str("a string, null, or an empty sequence")
        }

        fn visit_none<E>(self) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(None)
        }

        fn visit_unit<E>(self) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(None)
        }

        fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
        where
            D: Deserializer<'de>,
        {
            deserialize_debug_binding_name(deserializer)
        }

        fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(Some(value.to_owned()))
        }

        fn visit_string<E>(self, value: String) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            Ok(Some(value))
        }

        fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
        where
            A: SeqAccess<'de>,
        {
            if seq.next_element::<de::IgnoredAny>()?.is_none() {
                return Ok(None);
            }
            Err(de::Error::invalid_type(
                de::Unexpected::Seq,
                &"an empty sequence",
            ))
        }
    }

    deserializer.deserialize_any(BindingNameVisitor)
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DebugScalarRegistration {
    pub type_path: &'static str,
    pub field_type: &'static str,
    pub semantics: DebugFieldSemantics,
}

pub trait DebugScalarType: 'static {
    fn debug_scalar_registration() -> DebugScalarRegistration;
}

pub trait MatchingTasks {
    fn get_all_task_ids() -> &'static [&'static str];

    fn get_output_specs() -> &'static [TaskOutputSpec] {
        &[]
    }
}

/// Trait for providing JSON schemas for CopperList payload types.
///
/// This trait is implemented by the generated CuMsgs type via the `gen_cumsgs!` macro
/// when MCAP export support is enabled. It provides compile-time schema information
/// for each task's payload type, enabling proper schema generation for Foxglove.
///
/// The default implementation returns an empty vector for backwards compatibility
/// with code that doesn't need MCAP export support.
pub trait PayloadSchemas {
    /// Returns a vector of (task_id, schema_json) pairs.
    ///
    /// Each entry corresponds to a CopperList output slot, in slot order.
    /// The schema is a JSON Schema string generated from the payload type.
    fn get_payload_schemas() -> Vec<(&'static str, String)> {
        Vec::new()
    }
}

/// A CopperListTuple needs to be encodable, decodable and fixed size in memory.
pub trait CopperListTuple:
    bincode::Encode
    + bincode::Decode<()>
    + Debug
    + Serialize
    + ErasedCuStampedDataSet
    + MatchingTasks
    + Default
{
} // Decode forces Sized already

// Also anything that follows this contract can be a payload (blanket implementation)
impl<T> CopperListTuple for T where
    T: bincode::Encode
        + bincode::Decode<()>
        + Debug
        + Serialize
        + ErasedCuStampedDataSet
        + MatchingTasks
        + Default
{
}

// We use this type to convey very small status messages.
// MAX_SIZE from their repr module is not accessible so we need to copy paste their definition for 24
// which is the maximum size for inline allocation (no heap)
pub const COMPACT_STRING_CAPACITY: usize = size_of::<String>();

#[derive(Clone, Default, Serialize, Deserialize, PartialEq, Eq)]
pub struct CuCompactString(pub CompactString);

impl Encode for CuCompactString {
    fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
        let CuCompactString(compact_string) = self;
        let bytes = &compact_string.as_bytes();
        bytes.encode(encoder)
    }
}

impl Debug for CuCompactString {
    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
        if self.0.is_empty() {
            return write!(f, "CuCompactString(Empty)");
        }
        write!(f, "CuCompactString({})", self.0)
    }
}

impl<Context> Decode<Context> for CuCompactString {
    fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError> {
        let bytes = <Vec<u8> as Decode<D::Context>>::decode(decoder)?; // Decode into a byte buffer
        let compact_string =
            CompactString::from_utf8(bytes).map_err(|e| DecodeError::Utf8 { inner: e })?;
        Ok(CuCompactString(compact_string))
    }
}

impl<'de, Context> BorrowDecode<'de, Context> for CuCompactString {
    fn borrow_decode<D: BorrowDecoder<'de>>(decoder: &mut D) -> Result<Self, DecodeError> {
        CuCompactString::decode(decoder)
    }
}

#[cfg(feature = "defmt")]
impl defmt::Format for CuError {
    fn format(&self, f: defmt::Formatter) {
        match &self.cause {
            Some(c) => {
                let cause_str = c.to_string();
                defmt::write!(
                    f,
                    "CuError {{ message: {}, cause: {} }}",
                    defmt::Display2Format(&self.message),
                    defmt::Display2Format(&cause_str),
                )
            }
            None => defmt::write!(
                f,
                "CuError {{ message: {}, cause: None }}",
                defmt::Display2Format(&self.message),
            ),
        }
    }
}

#[cfg(feature = "defmt")]
impl defmt::Format for CuCompactString {
    fn format(&self, f: defmt::Formatter) {
        if self.0.is_empty() {
            defmt::write!(f, "CuCompactString(Empty)");
        } else {
            defmt::write!(f, "CuCompactString({})", defmt::Display2Format(&self.0));
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::CuCompactString;
    use bincode::{config, decode_from_slice, encode_to_vec};
    use compact_str::CompactString;

    #[test]
    fn test_cucompactstr_encode_decode_empty() {
        let cstr = CuCompactString(CompactString::from(""));
        let config = config::standard();
        let encoded = encode_to_vec(&cstr, config).expect("Encoding failed");
        assert_eq!(encoded.len(), 1); // This encodes the usize 0 in variable encoding so 1 byte which is 0.
        let (decoded, _): (CuCompactString, usize) =
            decode_from_slice(&encoded, config).expect("Decoding failed");
        assert_eq!(cstr.0, decoded.0);
    }

    #[test]
    fn test_cucompactstr_encode_decode_small() {
        let cstr = CuCompactString(CompactString::from("test"));
        let config = config::standard();
        let encoded = encode_to_vec(&cstr, config).expect("Encoding failed");
        assert_eq!(encoded.len(), 5); // This encodes a 4-byte string "test" plus 1 byte for the length prefix.
        let (decoded, _): (CuCompactString, usize) =
            decode_from_slice(&encoded, config).expect("Decoding failed");
        assert_eq!(cstr.0, decoded.0);
    }
}

// Tests that require std feature
#[cfg(all(test, feature = "std"))]
mod std_tests {
    use crate::{CuError, DebugFieldDescriptor, DebugFieldKind, DebugFieldSemantics, with_cause};
    use serde_json::json;

    #[test]
    fn test_cuerror_from_str() {
        let err = CuError::from("test error");
        assert_eq!(err.message(), "test error");
        assert!(err.cause().is_none());
    }

    #[test]
    fn test_cuerror_from_string() {
        let err = CuError::from(String::from("test error"));
        assert_eq!(err.message(), "test error");
        assert!(err.cause().is_none());
    }

    #[test]
    fn test_cuerror_new_index() {
        let err = CuError::new(42);
        assert_eq!(err.message(), "[interned:42]");
        assert!(err.cause().is_none());
    }

    #[test]
    fn test_cuerror_new_with_cause() {
        let io_err = std::io::Error::other("io error");
        let err = CuError::new_with_cause("wrapped error", io_err);
        assert_eq!(err.message(), "wrapped error");
        assert!(err.cause().is_some());
        assert!(err.cause().unwrap().to_string().contains("io error"));
    }

    #[test]
    fn test_cuerror_add_cause() {
        let err = CuError::from("base error").add_cause("additional context");
        assert_eq!(err.message(), "base error");
        assert!(err.cause().is_some());
        assert_eq!(err.cause().unwrap().to_string(), "additional context");
    }

    #[test]
    fn test_cuerror_with_cause_method() {
        let io_err = std::io::Error::other("io error");
        let err = CuError::from("base error").with_cause(io_err);
        assert_eq!(err.message(), "base error");
        assert!(err.cause().is_some());
    }

    #[test]
    fn test_cuerror_with_cause_free_function() {
        let io_err = std::io::Error::other("io error");
        let err = with_cause("wrapped", io_err);
        assert_eq!(err.message(), "wrapped");
        assert!(err.cause().is_some());
    }

    #[test]
    fn test_cuerror_clone() {
        let io_err = std::io::Error::other("io error");
        let err = CuError::new_with_cause("test", io_err);
        let cloned = err.clone();
        assert_eq!(err.message(), cloned.message());
        // Cause string representation should match
        assert_eq!(
            err.cause().map(|c| c.to_string()),
            cloned.cause().map(|c| c.to_string())
        );
    }

    #[test]
    fn test_cuerror_serialize_deserialize_json() {
        let io_err = std::io::Error::other("io error");
        let err = CuError::new_with_cause("test", io_err);

        let serialized = serde_json::to_string(&err).unwrap();
        let deserialized: CuError = serde_json::from_str(&serialized).unwrap();

        assert_eq!(err.message(), deserialized.message());
        // Cause should be preserved as string
        assert!(deserialized.cause().is_some());
    }

    #[test]
    fn test_cuerror_serialize_deserialize_no_cause() {
        let err = CuError::from("simple error");

        let serialized = serde_json::to_string(&err).unwrap();
        let deserialized: CuError = serde_json::from_str(&serialized).unwrap();

        assert_eq!(err.message(), deserialized.message());
        assert!(deserialized.cause().is_none());
    }

    #[test]
    fn test_cuerror_display() {
        let err = CuError::from("test error").add_cause("some context");
        let display = format!("{}", err);
        assert!(display.contains("test error"));
        assert!(display.contains("some context"));
    }

    #[test]
    fn test_cuerror_debug() {
        let err = CuError::from("test error").add_cause("some context");
        let debug = format!("{:?}", err);
        assert!(debug.contains("test error"));
        assert!(debug.contains("some context"));
    }

    #[test]
    fn debug_field_descriptor_skips_missing_binding_name_on_serialize() {
        let descriptor = DebugFieldDescriptor {
            display_path: "meta.process_time.start_ns".to_owned(),
            binding_name: None,
            field_type: "integer".to_owned(),
            value_type_path: "cu29_clock::CuTime".to_owned(),
            semantics: Some(DebugFieldSemantics::Time),
            nullable: true,
            kind: DebugFieldKind::Scalar,
            children: Vec::new(),
        };

        let encoded = serde_json::to_value(&descriptor).unwrap();
        assert!(encoded.get("binding_name").is_none());
    }

    #[test]
    fn debug_field_descriptor_accepts_empty_array_binding_name() {
        let encoded = json!({
            "display_path": "meta.process_time.start_ns",
            "binding_name": [],
            "field_type": "integer",
            "value_type_path": "cu29_clock::CuTime",
            "semantics": "Time",
            "nullable": true,
            "kind": "scalar",
        });

        let descriptor: DebugFieldDescriptor = serde_json::from_value(encoded).unwrap();
        assert_eq!(descriptor.binding_name, None);
        assert_eq!(descriptor.semantics, Some(DebugFieldSemantics::Time));
        assert_eq!(descriptor.kind, DebugFieldKind::Scalar);
        assert!(descriptor.children.is_empty());
    }
}