1 files changed, 193 insertions, 0 deletions
diff --git a/third_party/rust/anyhow/src/context.rs b/third_party/rust/anyhow/src/context.rs
new file mode 100644
index 0000000000..9df86937bd
--- /dev/null
+++ b/third_party/rust/anyhow/src/context.rs
@@ -0,0 +1,193 @@
+use crate::error::ContextError;
+use crate::{Context, Error, StdError};
+use core::convert::Infallible;
+use core::fmt::{self, Debug, Display, Write};
+
+#[cfg(backtrace)]
+use std::any::{Demand, Provider};
+
+mod ext {
+    use super::*;
+
+    pub trait StdError {
+        fn ext_context<C>(self, context: C) -> Error
+        where
+            C: Display + Send + Sync + 'static;
+    }
+
+    #[cfg(feature = "std")]
+    impl<E> StdError for E
+    where
+        E: std::error::Error + Send + Sync + 'static,
+    {
+        fn ext_context<C>(self, context: C) -> Error
+        where
+            C: Display + Send + Sync + 'static,
+        {
+            let backtrace = backtrace_if_absent!(&self);
+            Error::from_context(context, self, backtrace)
+        }
+    }
+
+    impl StdError for Error {
+        fn ext_context<C>(self, context: C) -> Error
+        where
+            C: Display + Send + Sync + 'static,
+        {
+            self.context(context)
+        }
+    }
+}
+
+impl<T, E> Context<T, E> for Result<T, E>
+where
+    E: ext::StdError + Send + Sync + 'static,
+{
+    fn context<C>(self, context: C) -> Result<T, Error>
+    where
+        C: Display + Send + Sync + 'static,
+    {
+        // Not using map_err to save 2 useless frames off the captured backtrace
+        // in ext_context.
+        match self {
+            Ok(ok) => Ok(ok),
+            Err(error) => Err(error.ext_context(context)),
+        }
+    }
+
+    fn with_context<C, F>(self, context: F) -> Result<T, Error>
+    where
+        C: Display + Send + Sync + 'static,
+        F: FnOnce() -> C,
+    {
+        match self {
+            Ok(ok) => Ok(ok),
+            Err(error) => Err(error.ext_context(context())),
+        }
+    }
+}
+
+/// ```
+/// # type T = ();
+/// #
+/// use anyhow::{Context, Result};
+///
+/// fn maybe_get() -> Option<T> {
+///     # const IGNORE: &str = stringify! {
+///     ...
+///     # };
+///     # unimplemented!()
+/// }
+///
+/// fn demo() -> Result<()> {
+///     let t = maybe_get().context("there is no T")?;
+///     # const IGNORE: &str = stringify! {
+///     ...
+///     # };
+///     # unimplemented!()
+/// }
+/// ```
+impl<T> Context<T, Infallible> for Option<T> {
+    fn context<C>(self, context: C) -> Result<T, Error>
+    where
+        C: Display + Send + Sync + 'static,
+    {
+        // Not using ok_or_else to save 2 useless frames off the captured
+        // backtrace.
+        match self {
+            Some(ok) => Ok(ok),
+            None => Err(Error::from_display(context, backtrace!())),
+        }
+    }
+
+    fn with_context<C, F>(self, context: F) -> Result<T, Error>
+    where
+        C: Display + Send + Sync + 'static,
+        F: FnOnce() -> C,
+    {
+        match self {
+            Some(ok) => Ok(ok),
+            None => Err(Error::from_display(context(), backtrace!())),
+        }
+    }
+}
+
+impl<C, E> Debug for ContextError<C, E>
+where
+    C: Display,
+    E: Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Error")
+            .field("context", &Quoted(&self.context))
+            .field("source", &self.error)
+            .finish()
+    }
+}
+
+impl<C, E> Display for ContextError<C, E>
+where
+    C: Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Display::fmt(&self.context, f)
+    }
+}
+
+impl<C, E> StdError for ContextError<C, E>
+where
+    C: Display,
+    E: StdError + 'static,
+{
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        Some(&self.error)
+    }
+
+    #[cfg(backtrace)]
+    fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+        StdError::provide(&self.error, demand);
+    }
+}
+
+impl<C> StdError for ContextError<C, Error>
+where
+    C: Display,
+{
+    fn source(&self) -> Option<&(dyn StdError + 'static)> {
+        Some(unsafe { crate::ErrorImpl::error(self.error.inner.by_ref()) })
+    }
+
+    #[cfg(backtrace)]
+    fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
+        Provider::provide(&self.error, demand);
+    }
+}
+
+struct Quoted<C>(C);
+
+impl<C> Debug for Quoted<C>
+where
+    C: Display,
+{
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_char('"')?;
+        Quoted(&mut *formatter).write_fmt(format_args!("{}", self.0))?;
+        formatter.write_char('"')?;
+        Ok(())
+    }
+}
+
+impl Write for Quoted<&mut fmt::Formatter<'_>> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        Display::fmt(&s.escape_debug(), self.0)
+    }
+}
+
+pub(crate) mod private {
+    use super::*;
+
+    pub trait Sealed {}
+
+    impl<T, E> Sealed for Result<T, E> where E: ext::StdError {}
+    impl<T> Sealed for Option<T> {}
+}