rootcause/

markers.rs

//! Marker types and traits for defining ownership and thread-safety semantics.
//!
//! This module provides type-level markers that control how reports and
//! attachments behave with respect to ownership, cloning, and thread safety.
//! These markers are used as generic parameters in types like [`Report<C, O,
//! T>`](crate::Report) to encode compile-time guarantees about how data can be
//! accessed and shared.
//!
//! # Design Philosophy
//!
//! The constraints encoded by these markers are enforced at construction time.
//! It is impossible to construct a [`Report`](crate::Report),
//! [`ReportRef`], or
//! [`ReportCollection`] that violates the invariants
//! associated with its marker types. This means you can trust that a
//! `Report<_, _, SendSync>` truly is `Send + Sync`, and that a `Report<_,
//! Mutable>` truly has unique ownership.
//!
//! [`ReportRef`]: crate::ReportRef
//! [`ReportCollection`]: crate::report_collection::ReportCollection
//!
//! # Context Marker
//!
//! The context marker is the first type parameter (`C`) in [`Report<C, O,
//! T>`](crate::Report) and determines what type of error is stored at the root:
//!
//! - [`Dynamic`]: Type-erased context - the root error can be any type (like
//!   [`anyhow::Error`]). This is the default when you write just [`Report`].
//! - Any concrete type: Typed context - the root error must be that specific
//!   type (like [`error-stack`]).
//!
//! See the [`Dynamic`] documentation for a detailed comparison and usage
//! examples.
//!
//! [`anyhow::Error`]: https://docs.rs/anyhow
//! [`error-stack`]: https://docs.rs/error-stack
//! [`Report`]: crate::Report
//!
//! # Ownership Markers
//!
//! Ownership markers control whether reports and report references can be
//! mutated and cloned.
//!
//! For owned reports ([`Report<C, O, T>`](crate::Report)), the ownership marker
//! `O` can be:
//! - [`Mutable`]: Unique ownership - the report can be mutated but not cloned
//! - [`Cloneable`]: Shared ownership - the report can be cloned but not mutated
//!
//! For report references ([`ReportRef<C, O>`](crate::ReportRef)), the ownership
//! marker `O` can be:
//! - [`Cloneable`]: Enables [`clone_arc`](crate::ReportRef::clone_arc) to get
//!   an owned report
//! - [`Uncloneable`]: Does not provide
//!   [`clone_arc`](crate::ReportRef::clone_arc)
//!
//! # Thread Safety Markers
//!
//! Thread safety markers control whether reports can be sent between threads or
//! shared across threads. These appear as the third type parameter (`T`) in
//! [`Report<C, O, T>`](crate::Report):
//!
//! - [`SendSync`]: The report and all its contents are `Send + Sync`, allowing
//!   the report to cross thread boundaries.
//! - [`Local`]: The report contains non-thread-safe data (like `Rc` or raw
//!   pointers) and cannot be sent between threads.
//!
//! # Examples
//!
//! ## Creating Reports with Different Ownership Semantics
//!
//! ```
//! use rootcause::prelude::*;
//!
//! // Mutable report - can be modified by adding context and attachments
//! let mut report: Report<String, markers::Mutable> = report!("Error".to_string());
//! let report: Report<String, markers::Mutable> = report.attach("Additional context");
//!
//! // Convert to cloneable report - can be cloned but not mutated
//! let cloneable: Report<String, markers::Cloneable> = report.into_cloneable();
//! let cloned: Report<String, markers::Cloneable> = cloneable.clone();
//! assert_eq!(format!("{}", cloneable), format!("{}", cloned));
//! ```
//!
//! ## Working with Thread Safety
//!
//! ```
//! use std::rc::Rc;
//!
//! use rootcause::prelude::*;
//!
//! // Thread-safe report with String (String is Send + Sync)
//! let thread_safe: Report<String, markers::Mutable, markers::SendSync> =
//!     report!("Thread-safe error".to_string());
//!
//! // Can be sent to another thread
//! std::thread::spawn(move || {
//!     println!("{}", thread_safe);
//! });
//!
//! // Local report with Rc (Rc is !Send + !Sync)
//! let local_data: Rc<String> = Rc::new("Not thread-safe".to_string());
//! let local_report: Report<Rc<String>, markers::Mutable, markers::Local> = report!(local_data);
//! // local_report cannot be sent to another thread - won't compile
//! ```

use crate::ReportMut;

/// Marker type for reports with dynamic (type-erased) context.
///
/// [`Dynamic`] is used as the context type parameter in
/// [`Report<Dynamic, O, T>`](crate::Report) to indicate that the actual error
/// type at the root is not known at compile time. This is the default behavior
/// and is similar to [`anyhow::Error`] - any error type
/// can be stored and the `?` operator works automatically.
///
/// # Key Properties
///
/// - **Zero-cost type erasure**: No actual instance of [`Dynamic`] is ever
///   stored. It's purely a marker type used at the type level.
/// - **Automatic conversions**: The `?` operator automatically converts any
///   error type into `Report<Dynamic>`.
/// - **Flexible propagation**: When you just need errors to propagate upward
///   with context, [`Dynamic`] is the right choice.
///
/// # When to Use Dynamic
///
/// Use `Report<Dynamic>` (or just [`Report`](crate::Report), which defaults to
/// [`Dynamic`]) when:
/// - You're propagating errors upward and don't need to pattern match on
///   specific error types
/// - You want the flexibility to return different error types from the same
///   function
/// - You're building applications where error handling is about logging and
///   displaying, not recovery
///
/// Use `Report<YourErrorType>` instead when:
/// - Callers need to pattern match on specific error variants for recovery
/// - You want compile-time guarantees about which errors a function can return
/// - You're building libraries with well-defined error types
///
/// See [`examples/typed_reports.rs`] for when typed errors are appropriate.
///
/// [`examples/typed_reports.rs`]: https://github.com/rootcause-rs/rootcause/blob/main/examples/typed_reports.rs
///
/// # Examples
///
/// ## Basic Usage
///
/// ```
/// use rootcause::prelude::*;
///
/// // Report<Dynamic> is the default - these are equivalent:
/// fn might_fail() -> Result<(), Report> {
///     // Can return any error type via ?
///     std::fs::read_to_string("/nonexistent")?;
///     Ok(())
/// }
///
/// fn might_fail_explicit() -> Result<(), Report<markers::Dynamic>> {
///     std::fs::read_to_string("/nonexistent")?;
///     Ok(())
/// }
/// ```
///
/// ## Mixing Error Types
///
/// ```
/// use std::{fs, io};
///
/// use rootcause::prelude::*;
///
/// #[derive(Debug)]
/// struct ConfigError(String);
/// impl std::fmt::Display for ConfigError {
///     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
///         write!(f, "Config error: {}", self.0)
///     }
/// }
/// impl std::error::Error for ConfigError {}
///
/// fn load_and_parse(path: &str) -> Result<u32, Report> {
///     // io::Error from fs operations
///     let contents = fs::read_to_string(path)?;
///
///     // Custom ConfigError
///     if contents.is_empty() {
///         Err(ConfigError("empty file".into()))?;
///     }
///
///     // ParseIntError from parse
///     let value: u32 = contents.trim().parse()?;
///
///     Ok(value)
/// }
/// ```
///
/// ## Converting Between Typed and Dynamic
///
/// ```
/// use rootcause::prelude::*;
///
/// #[derive(Debug)]
/// struct MyError;
/// impl std::fmt::Display for MyError {
///     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
///         write!(f, "MyError")
///     }
/// }
/// impl std::error::Error for MyError {}
///
/// fn typed_error() -> Result<(), Report<MyError>> {
///     Err(report!(MyError))
/// }
///
/// fn dynamic_error() -> Result<(), Report> {
///     // Typed report automatically coerces to dynamic via ?
///     typed_error()?;
///     Ok(())
/// }
///
/// // Or convert explicitly:
/// fn explicit_conversion() -> Result<(), Report> {
///     let typed: Report<MyError> = report!(MyError);
///     let dynamic: Report = typed.into_dynamic();
///     Err(dynamic)
/// }
/// ```
///
/// See [`examples/error_coercion.rs`] for a complete guide to type conversions.
///
/// [`examples/error_coercion.rs`]: https://github.com/rootcause-rs/rootcause/blob/main/examples/error_coercion.rs
pub struct Dynamic {
    /// This field ensures [`Dynamic`] is an unsized type.
    ///
    /// Since the [`Dynamic`] type itself is never instantiated, the choice
    /// of an unsized type here is purely to enforce that property at the type
    /// level.
    _phantom_unsized: [()],
}

/// Marker type for owned reports with unique ownership.
///
/// This marker is used exclusively with [`Report<C, Mutable, T>`] (not
/// [`ReportRef`]). It indicates that the report has unique ownership of its
/// data, which allows mutation operations but prevents cloning.
///
/// [`Report<C, Mutable, T>`]: crate::Report
/// [`ReportRef`]: crate::ReportRef
///
/// # Available Operations
///
/// With [`Mutable`] ownership, you can:
/// - Add attachments with [`attach`](crate::Report::attach)
/// - Add parent context with [`context`](crate::Report::context)
/// - Get mutable access with [`as_mut`](crate::Report::as_mut)
/// - Convert to [`Cloneable`] with
///   [`into_cloneable`](crate::Report::into_cloneable)
///
/// # Examples
///
/// ```
/// use rootcause::prelude::*;
///
/// let report: Report<String, markers::Mutable> = report!("Database error".to_string());
///
/// // Can add attachments (consumes and returns the report)
/// let report: Report<String, markers::Mutable> = report.attach("connection timeout");
///
/// // Can add parent context
/// let report: Report<String, markers::Mutable> =
///     report.context("Failed to fetch user data".to_string());
///
/// // Cannot clone - Mutable reports don't implement Clone
/// // let cloned = report.clone(); // ❌ Won't compile
/// ```
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Default, Hash)]
pub struct Mutable;

/// Marker type for cloneable reports and report references.
///
/// This marker is used with both [`Report<C, Cloneable, T>`](crate::Report) and
/// [`ReportRef<C, Cloneable>`](crate::ReportRef). It indicates shared ownership
/// using reference counting (`Arc` internally), which allows cheap cloning but
/// prevents mutation.
///
/// # Usage with Report
///
/// For [`Report<C, Cloneable, T>`](crate::Report), this marker means the report
/// itself implements `Clone`, allowing you to cheaply clone the entire report
/// (shallow copy via `Arc`).
///
/// # Usage with ReportRef
///
/// For [`ReportRef<C, Cloneable>`](crate::ReportRef), the marker enables the
/// [`clone_arc`](crate::ReportRef::clone_arc) method, which clones the
/// underlying `Arc` to produce an owned [`Report<C, Cloneable,
/// T>`](crate::Report). Note that [`ReportRef`](crate::ReportRef) itself is
/// always `Copy` and `Clone` regardless of the ownership marker - the
/// [`Cloneable`] marker specifically enables converting the reference back to
/// an owned report.
///
/// # When to Use
///
/// Use [`Cloneable`] reports when you need to:
/// - Share an error report across multiple code paths
/// - Store reports in collections that require `Clone`
/// - Return the same error from multiple places without deep copying
///
/// # Converting to Cloneable
///
/// Convert a [`Mutable`] report to [`Cloneable`] using
/// [`into_cloneable`](crate::Report::into_cloneable):
///
/// ```
/// use rootcause::prelude::*;
///
/// let report: Report<String, markers::Mutable> = report!("Error".to_string());
///
/// // Convert to cloneable
/// let cloneable: Report<String, markers::Cloneable> = report.into_cloneable();
///
/// // Now can clone cheaply (shallow clone via Arc)
/// let clone1: Report<String, markers::Cloneable> = cloneable.clone();
/// let clone2: Report<String, markers::Cloneable> = cloneable.clone();
/// ```
///
/// # Examples
///
/// Cloning owned reports:
///
/// ```
/// use rootcause::prelude::*;
///
/// fn process_error(error: Report<String, markers::Cloneable>) {
///     // Can clone the error to pass to multiple handlers
///     let for_logging = error.clone();
///     let for_metrics = error.clone();
///
///     println!("Logging: {}", for_logging);
///     println!("Metrics: {}", for_metrics);
/// }
///
/// let report: Report<String> = report!("An error occurred".to_string());
/// process_error(report.into_cloneable());
/// ```
///
/// Using [`clone_arc`](crate::ReportRef::clone_arc) on report references:
///
/// ```
/// use rootcause::{ReportRef, prelude::*};
///
/// let report: Report<String, markers::Cloneable> = report!("Error".to_string()).into_cloneable();
///
/// // Get a reference (ReportRef is Copy, so this is cheap)
/// let report_ref: ReportRef<String, markers::Cloneable> = report.as_ref();
///
/// // Clone the underlying Arc to get an owned Report
/// let owned: Report<String, markers::Cloneable> = report_ref.clone_arc();
/// ```
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Default, Hash)]
pub struct Cloneable;

/// Marker type for non-cloneable report references.
///
/// This marker is used exclusively with [`ReportRef<C,
/// Uncloneable>`](crate::ReportRef) (not [`Report`](crate::Report)). It
/// indicates that the reference does not provide the
/// [`clone_arc`](crate::ReportRef::clone_arc) method to obtain an owned report.
///
/// Note that [`ReportRef`](crate::ReportRef) itself is always `Copy` and
/// `Clone` - you can always copy the reference itself. The [`Uncloneable`]
/// marker only prevents cloning the underlying `Arc` to get an owned
/// [`Report`](crate::Report).
///
/// # Common Uses
///
/// [`Uncloneable`] references typically arise in two situations:
///
/// 1. **Taking a reference to a [`Mutable`] report**: When you call
///    [`as_ref`](crate::Report::as_ref) on a `Report<C, Mutable>`, you get a
///    `ReportRef<C, Uncloneable>` because the underlying report has unique
///    ownership.
///
/// 2. **Explicitly restricting cloneability**: You can convert a `ReportRef<C,
///    Cloneable>` to `ReportRef<C, Uncloneable>` when you want to pass a
///    reference that explicitly cannot use
///    [`clone_arc`](crate::ReportRef::clone_arc), ensuring the recipient
///    can only inspect the report without obtaining ownership. This can be
///    useful in APIs that need to accept both cloneable and uncloneable
///    references.
///
///
/// # Examples
///
/// Taking a reference to a [`Mutable`] report:
///
/// ```
/// use rootcause::{ReportRef, prelude::*};
///
/// let report: Report<String, markers::Mutable> = report!("An error occurred".to_string());
///
/// // Taking a reference to a Mutable report gives an Uncloneable reference
/// let report_ref: ReportRef<String, markers::Uncloneable> = report.as_ref();
///
/// // The reference itself can be copied (ReportRef is Copy)
/// let copy = report_ref;
///
/// // But you cannot clone the underlying Arc to get an owned Report
/// // let owned = report_ref.clone_arc(); // ❌ Method not available
/// ```
///
/// Explicitly converting to [`Uncloneable`]:
///
/// ```
/// use rootcause::{ReportRef, prelude::*};
///
/// let report: Report<String, markers::Cloneable> = report!("Error".to_string()).into_cloneable();
///
/// let cloneable_ref: ReportRef<String, markers::Cloneable> = report.as_ref();
///
/// // Convert to uncloneable to restrict the recipient's ability to clone
/// let uncloneable_ref: ReportRef<String, markers::Uncloneable> = cloneable_ref.into_uncloneable();
/// ```
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Default, Hash)]
pub struct Uncloneable;

/// Marker type indicating that a report and all its contents are `Send + Sync`.
///
/// This is the default thread-safety marker for reports. When all the context
/// objects and attachments in a report implement `Send + Sync`, the report
/// itself can be safely sent to other threads and shared between threads.
///
/// # When to Use
///
/// Most standard types in Rust are `Send + Sync`, including:
/// - Primitive types (`i32`, `String`, `Vec`, etc.)
/// - Most standard library types
/// - Types explicitly designed for concurrent use
///
/// Use [`SendSync`] (the default) unless you have a specific need for
/// thread-local data.
///
/// # Examples
///
/// ```
/// use std::thread;
///
/// use rootcause::prelude::*;
///
/// // String is Send + Sync, so the report is too
/// let report: Report<String, markers::Mutable, markers::SendSync> =
///     report!("Thread-safe error".to_string());
///
/// // Can send to another thread
/// thread::spawn(move || {
///     println!("Error in thread: {}", report);
/// })
/// .join()
/// .unwrap();
/// ```
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Default, Hash)]
pub struct SendSync;

/// Marker type indicating that a report is not `Send` or `Sync`.
///
/// This marker is used when a report contains thread-local data that cannot be
/// safely sent between threads or shared across threads. Common examples
/// include `Rc`, raw pointers, or types that explicitly opt out of
/// `Send`/`Sync`.
///
/// # When to Use
///
/// Use [`Local`] when your error context or attachments contain:
/// - `Rc<T>` or `Weak<T>` (use `Arc<T>` for thread-safe alternative)
/// - Raw pointers (`*const T`, `*mut T`)
/// - Types that wrap thread-local storage
/// - Any type that is `!Send` or `!Sync`
///
/// # Converting to Local
///
/// You can convert a thread-safe report to a local one using
/// [`into_local`](crate::Report::into_local), or create a local report directly
/// when the context type is not `Send + Sync`.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// use rootcause::prelude::*;
///
/// // Rc is not Send or Sync, so the report must be Local
/// let local_data: Rc<String> = Rc::new("Thread-local error".to_string());
/// let report: Report<Rc<String>, markers::Mutable, markers::Local> = report!(local_data);
///
/// // This report cannot be sent to another thread
/// // std::thread::spawn(move || {
/// //     println!("{}", report); // ❌ Won't compile
/// // });
/// ```
///
/// Converting a thread-safe report to local:
///
/// ```
/// use std::rc::Rc;
///
/// use rootcause::prelude::*;
///
/// let report: Report<String> = report!("Error".to_string());
///
/// // Convert to local report so we can use thread-local data
/// let local_report: Report<String, markers::Mutable, markers::Local> = report.into_local();
/// ```
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Default, Hash)]
pub struct Local;

mod sealed_report_ownership_marker {
    use super::*;

    pub trait Sealed: 'static {}

    impl Sealed for Mutable {}
    impl Sealed for Cloneable {}
}

mod sealed_object_marker {
    pub trait Sealed: 'static {}

    impl<C: Sized + 'static> Sealed for C {}
}

/// Marker trait for ownership semantics of owned reports.
///
/// This trait is implemented for [`Mutable`] and [`Cloneable`], the two
/// ownership markers that can be used with [`Report<C, O, T>`](crate::Report).
/// It exists primarily to enable the associated type `RefMarker`, which
/// determines the ownership marker used when creating a reference to the
/// report.
///
/// # Relationship to Report Construction
///
/// While this trait defines the ownership modes, the actual enforcement of
/// ownership invariants happens at report construction time. It is impossible
/// to construct a `Report<_, Mutable>` that doesn't have unique ownership, or a
/// `Report<_, Cloneable>` that hasn't been properly set up for shared
/// ownership.
///
/// # Ownership Modes
///
/// - [`Mutable`]: Indicates unique ownership. The report can be mutated but not
///   cloned. Methods like [`attach`](crate::Report::attach) and
///   [`as_mut`](crate::Report::as_mut) are only available in this mode.
///
/// - [`Cloneable`]: Indicates shared ownership via reference counting. The
///   report can be cloned cheaply but cannot be mutated since there may be
///   multiple references.
///
/// # Associated Types
///
/// The `RefMarker` associated type determines what kind of reference you get
/// when calling [`as_ref`](crate::Report::as_ref):
/// - For [`Mutable`], this is [`Uncloneable`] (the reference cannot use
///   [`clone_arc`](crate::ReportRef::clone_arc))
/// - For [`Cloneable`], this is [`Cloneable`] (the reference can use
///   [`clone_arc`](crate::ReportRef::clone_arc))
///
/// # Implementation
///
/// This trait is sealed and cannot be implemented outside of this crate. You
/// should use the provided implementations for [`Mutable`] and [`Cloneable`].
///
/// # Examples
///
/// [`ReportOwnershipMarker`] is typically used as a bound to write functions
/// that accept both [`Mutable`] and [`Cloneable`] reports:
///
/// ```
/// use rootcause::{
///     markers::{Cloneable, Mutable, ReportOwnershipMarker},
///     prelude::*,
/// };
///
/// fn describe<O: ReportOwnershipMarker>(report: Report<&'static str, O>) -> String {
///     report.current_context().to_string()
/// }
///
/// let context: &'static str = "oops";
/// let mutable: Report<&str, Mutable> = report!(context);
/// assert_eq!(describe(mutable), "oops");
///
/// let cloneable: Report<&str, Cloneable> = report!(context).into_cloneable();
/// assert_eq!(describe(cloneable), "oops");
/// ```
pub trait ReportOwnershipMarker: sealed_report_ownership_marker::Sealed {
    /// The ownership marker for references to this report type.
    ///
    /// This determines what type of reference is created when you call
    /// [`Report::as_ref`](crate::Report::as_ref):
    ///
    /// - For [`Mutable`]: Returns [`ReportRef<C,
    ///   Uncloneable>`](crate::ReportRef) because the underlying report has
    ///   unique ownership
    /// - For [`Cloneable`]: Returns [`ReportRef<C,
    ///   Cloneable>`](crate::ReportRef) because the underlying report already
    ///   uses shared ownership
    type RefMarker;
}
impl ReportOwnershipMarker for Mutable {
    type RefMarker = Uncloneable;
}
impl ReportOwnershipMarker for Cloneable {
    type RefMarker = Cloneable;
}

/// Marker trait combining object and thread-safety requirements.
///
/// This trait enforces thread-safety constraints for context and attachment
/// data at report construction time. Reports can only be constructed when their
/// context and attachments satisfy the requirements of the thread-safety
/// marker.
///
/// # Implementations
///
/// - For `T = Local`: Implemented for all `Sized + 'static` types, regardless
///   of their `Send`/`Sync` status. This allows using types like `Rc` in local
///   reports.
///
/// - For `T = SendSync`: Implemented only for `Sized + 'static` types that are
///   also `Send + Sync`. This ensures thread-safe reports can only be
///   constructed with thread-safe data.
///
/// # Enforcement at Construction
///
/// The key insight is that this trait is used as a bound during report
/// construction. You cannot create a `Report<C, _, SendSync>` unless `C:
/// ObjectMarkerFor<SendSync>`, which requires `C: Send + Sync`. This makes it
/// impossible to accidentally create an invalid report:
///
/// ```compile_fail
/// use std::rc::Rc;
/// use rootcause::prelude::*;
///
/// // This won't compile because Rc is not Send + Sync
/// let rc_data: Rc<String> = Rc::new("error".to_string());
/// let report: Report<Rc<String>, markers::Mutable, markers::SendSync> = report!(rc_data);
/// ```
///
/// Use [`Local`] instead for non-thread-safe data:
///
/// ```
/// use std::rc::Rc;
///
/// use rootcause::prelude::*;
///
/// let rc_data: Rc<String> = Rc::new("error".to_string());
/// let report: Report<Rc<String>, markers::Mutable, markers::Local> = report!(rc_data);
/// ```
//
// # Safety:
//
// This trait is sealed and cannot be implemented outside of this crate. It is
// guaranteed to only be implemented for the combinations of types and
// thread-safety markers listed above.
pub trait ObjectMarkerFor<T>: sealed_object_marker::Sealed + Sized + 'static {
    /// Runs report creation hooks specific to this thread-safety marker.
    #[doc(hidden)]
    #[track_caller]
    fn run_creation_hooks(report: ReportMut<'_, Dynamic, T>);
}

impl<O: Sized + 'static> ObjectMarkerFor<Local> for O {
    #[inline(always)]
    fn run_creation_hooks(report: ReportMut<'_, Dynamic, Local>) {
        crate::hooks::report_creation::run_creation_hooks_local(report);
    }
}

impl<O: Sized + 'static> ObjectMarkerFor<SendSync> for O
where
    O: Send + Sync,
{
    #[inline(always)]
    fn run_creation_hooks(report: ReportMut<'_, Dynamic, SendSync>) {
        crate::hooks::report_creation::run_creation_hooks_sendsync(report);
    }
}