From 7fae60fd8462f95cf3140c6a3b9eb06cb7953405 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jalil=20David=20Salam=C3=A9=20Messina?=
 <60845989+jalil-salame@users.noreply.github.com>
Date: Wed, 27 Nov 2024 04:55:24 +0100
Subject: [PATCH] feat(report): Implement `WrapError` for `Option` (#409)

Fixes: https://github.com/zkat/miette/issues/408

Implement `WrapError` for `Option<T>`. This is inline with `anyhow` that
also implements `Context` for `Option<T>`.

The implementation requires us to introduce a `DisplayError` internal
only type, that creates an error from a type that only implements
`Display` (`Report::from_adhoc` requires the type to also implement
`Debug`, but `WrapError` only requires it to implement `Display`).

For this I copied `MessageError` and adapted it to implement `Debug`
using the underlying type's `Display` impl. This is a bit of a hack, but
anyhow does [something similar][1].

[1]: https://docs.rs/anyhow/latest/src/anyhow/wrapper.rs.html#34
---
 src/eyreish/context.rs | 38 ++++++++++++++++++++++++++++++++++++++
 src/eyreish/wrapper.rs | 24 ++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/src/eyreish/context.rs b/src/eyreish/context.rs
index 3d9238b2..ee1fa08d 100644
--- a/src/eyreish/context.rs
+++ b/src/eyreish/context.rs
@@ -38,6 +38,44 @@ mod ext {
     }
 }
 
+impl<T> WrapErr<T, std::convert::Infallible> for Option<T> {
+    fn wrap_err<D>(self, msg: D) -> Result<T, Report>
+    where
+        D: Display + Send + Sync + 'static,
+    {
+        match self {
+            Some(t) => Ok(t),
+            None => Err(Report::from(crate::eyreish::wrapper::DisplayError(msg))),
+        }
+    }
+
+    fn wrap_err_with<D, F>(self, msg: F) -> Result<T, Report>
+    where
+        D: Display + Send + Sync + 'static,
+        F: FnOnce() -> D,
+    {
+        match self {
+            Some(t) => Ok(t),
+            None => Err(Report::from(crate::eyreish::wrapper::DisplayError(msg()))),
+        }
+    }
+
+    fn context<D>(self, msg: D) -> Result<T, Report>
+    where
+        D: Display + Send + Sync + 'static,
+    {
+        self.wrap_err(msg)
+    }
+
+    fn with_context<D, F>(self, msg: F) -> Result<T, Report>
+    where
+        D: Display + Send + Sync + 'static,
+        F: FnOnce() -> D,
+    {
+        self.wrap_err_with(msg)
+    }
+}
+
 impl<T, E> WrapErr<T, E> for Result<T, E>
 where
     E: ext::Diag + Send + Sync + 'static,
diff --git a/src/eyreish/wrapper.rs b/src/eyreish/wrapper.rs
index 62cf7a4b..bab73208 100644
--- a/src/eyreish/wrapper.rs
+++ b/src/eyreish/wrapper.rs
@@ -6,6 +6,30 @@ use crate::{Diagnostic, LabeledSpan, Report, SourceCode};
 
 use crate as miette;
 
+#[repr(transparent)]
+pub(crate) struct DisplayError<M>(pub(crate) M);
+
+impl<M> Debug for DisplayError<M>
+where
+    M: Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
+impl<M> Display for DisplayError<M>
+where
+    M: Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
+impl<M> StdError for DisplayError<M> where M: Display + 'static {}
+impl<M> Diagnostic for DisplayError<M> where M: Display + 'static {}
+
 #[repr(transparent)]
 pub(crate) struct MessageError<M>(pub(crate) M);