TypedReport: a dream that can never be :(

Basically, the idea was to have something like 'Report' that would
be strongly typed, except I ran into the exact same reason that anyhow
doesn't do this: the blanket `From` impl :(

So this is, in essence, impossible to do ergonomically, but I'm keeping
this around for future reference.

src/lib.rs

@@ -1,4 +1,4 @@
-#![deny(missing_docs, missing_debug_implementations, nonstandard_style)]
+// #![deny(missing_docs, missing_debug_implementations, nonstandard_style)]
 #![warn(unreachable_pub, rust_2018_idioms)]
 #![allow(unexpected_cfgs)]
 //! You run miette? You run her code like the software? Oh. Oh! Error code for
@@ -804,3 +804,6 @@ mod named_source;
 mod panic;
 mod protocol;
 mod source_impls;
+mod typed_report;
+
+pub use typed_report::*;

src/typed_report.rs

@@ -0,0 +1,68 @@
+use std::any::{Any, TypeId};
+use std::backtrace::Backtrace;
+use std::error::Error;
+use std::ops::Deref;
+
+pub type TypedResult<T, E> = Result<T, TypedReport<E>>;
+
+pub struct TypedReport<T: Error + 'static> {
+    error: T,
+    backtrace: Backtrace,
+}
+
+impl<T: Error + 'static> TypedReport<T> {
+    pub fn unwrap(self) -> T {
+        self.error
+    }
+
+    pub fn inner(&self) -> &T {
+        self.error.as_ref()
+    }
+
+    pub fn backtrace(&self) -> &Backtrace {
+       self.backtrace.as_ref()
+    }
+}
+
+impl<T: Error + 'static> Deref for TypedReport<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.error.as_ref().unwrap()
+    }
+}
+
+impl<T, U, V> From<U> for TypedReport<T>
+where
+    T: Any + Error + 'static,
+    U: Any + Error + 'static,
+    V: Any + Error + 'static + From<T>,
+{
+    fn from(value: U) -> Self {
+        let val = if TypeId::of::<U>() == TypeId::of::<TypedReport<V>>() {
+            value.unwrap().into()
+        } else {
+            value
+        };
+        TypedReport {
+            error: val,
+            backtrace: Backtrace::capture(),
+        }
+    }
+}
+
+impl<T, U> From<TypedReport<T>> for TypedReport<U>
+where
+    T: Any + Error + 'static,
+    U: Any + Error + 'static + From<T>,
+{
+    fn from(value: TypedReport<T>) -> Self {
+        if TypeId::of::<T>() == TypeId::of::<U>() {
+            return value
+        }
+        TypedReport {
+            error: value.error.take().map(|x| x.into()),
+            backtrace: value.backtrace.take(),
+        }
+    }
+}

tests/typed_report.rs

@@ -0,0 +1,44 @@
+use miette::{Diagnostic, TypedReport};
+use thiserror::Error;
+
+#[test]
+fn into_typed() {
+    #[derive(Debug, Diagnostic, Error)]
+    #[error("oops!")]
+    #[diagnostic(code(error::on::base))]
+    struct MyBad {
+        #[source_code]
+        src: String,
+        #[label("this bit here")]
+        highlight: (usize, usize),
+    }
+
+    let src = "source\n  text\n    here".to_string();
+    let err = MyBad {
+        src,
+        highlight: (9, 4),
+    };
+    let typed_err: TypedReport<_> = err.into();
+    assert_eq!(typed_err.code().unwrap().to_string(), "error::on::base");
+}
+
+#[test]
+fn backtrace_retention() {
+    #[derive(Debug, Error)]
+    #[error("oops!")]
+    struct MyBad;
+
+    #[derive(Debug, Error)]
+    #[error("also fail: {0}")]
+    struct AlsoBad(#[from] MyBad);
+
+    let typed_err: TypedReport<_> = MyBad.into();
+    let backtrace1 = typed_err.backtrace().to_string();
+
+    let other: TypedReport<AlsoBad> = typed_err.into();
+
+    let backtrace2 = other.backtrace().to_string();
+
+    assert_eq!(backtrace1, backtrace2);
+}
+