use core::convert::Infallible;
use crate::alloc::{AllocError, LayoutError};
-use crate::any::TypeId;
+use crate::any::{Demand, Provider, TypeId};
use crate::backtrace::Backtrace;
use crate::borrow::Cow;
use crate::cell;
fn cause(&self) -> Option<&dyn Error> {
self.source()
}
+
+ /// Provides type based access to context intended for error reports.
+ ///
+ /// Used in conjunction with [`Demand::provide_value`] and [`Demand::provide_ref`] to extract
+ /// references to member variables from `dyn Error` trait objects.
+ ///
+ /// # Example
+ ///
+ /// ```rust
+ /// #![feature(provide_any)]
+ /// #![feature(error_generic_member_access)]
+ /// use core::fmt;
+ /// use core::any::Demand;
+ ///
+ /// #[derive(Debug)]
+ /// struct MyBacktrace {
+ /// // ...
+ /// }
+ ///
+ /// impl MyBacktrace {
+ /// fn new() -> MyBacktrace {
+ /// // ...
+ /// # MyBacktrace {}
+ /// }
+ /// }
+ ///
+ /// #[derive(Debug)]
+ /// struct SourceError {
+ /// // ...
+ /// }
+ ///
+ /// impl fmt::Display for SourceError {
+ /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ /// write!(f, "Example Source Error")
+ /// }
+ /// }
+ ///
+ /// impl std::error::Error for SourceError {}
+ ///
+ /// #[derive(Debug)]
+ /// struct Error {
+ /// source: SourceError,
+ /// backtrace: MyBacktrace,
+ /// }
+ ///
+ /// impl fmt::Display for Error {
+ /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ /// write!(f, "Example Error")
+ /// }
+ /// }
+ ///
+ /// impl std::error::Error for Error {
+ /// fn provide<'a>(&'a self, req: &mut Demand<'a>) {
+ /// req
+ /// .provide_ref::<MyBacktrace>(&self.backtrace)
+ /// .provide_ref::<dyn std::error::Error + 'static>(&self.source);
+ /// }
+ /// }
+ ///
+ /// fn main() {
+ /// let backtrace = MyBacktrace::new();
+ /// let source = SourceError {};
+ /// let error = Error { source, backtrace };
+ /// let dyn_error = &error as &dyn std::error::Error;
+ /// let backtrace_ref = dyn_error.request_ref::<MyBacktrace>().unwrap();
+ ///
+ /// assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
+ /// }
+ /// ```
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ #[allow(unused_variables)]
+ fn provide<'a>(&'a self, req: &mut Demand<'a>) {}
+}
+
+#[unstable(feature = "error_generic_member_access", issue = "99301")]
+impl Provider for dyn Error + 'static {
+ fn provide<'a>(&'a self, req: &mut Demand<'a>) {
+ self.provide(req)
+ }
}
mod private {
None
}
}
+
+ /// Request a reference of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
+ core::any::request_ref(self)
+ }
+
+ /// Request a value of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_value<T: 'static>(&self) -> Option<T> {
+ core::any::request_value(self)
+ }
}
impl dyn Error + 'static + Send {
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
<dyn Error + 'static>::downcast_mut::<T>(self)
}
+
+ /// Request a reference of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
+ <dyn Error + 'static>::request_ref(self)
+ }
+
+ /// Request a value of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_value<T: 'static>(&self) -> Option<T> {
+ <dyn Error + 'static>::request_value(self)
+ }
}
impl dyn Error + 'static + Send + Sync {
pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
<dyn Error + 'static>::downcast_mut::<T>(self)
}
+
+ /// Request a reference of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
+ <dyn Error + 'static>::request_ref(self)
+ }
+
+ /// Request a value of type `T` as context about this error.
+ #[unstable(feature = "error_generic_member_access", issue = "99301")]
+ pub fn request_value<T: 'static>(&self) -> Option<T> {
+ <dyn Error + 'static>::request_value(self)
+ }
}
impl dyn Error {