From a728f72f62d35ec03c623fcb5244dff30b0fed84 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20S=C3=A1=20de=20Mello?= <codasm@pm.me>
Date: Mon, 18 Nov 2024 15:37:18 +0000
Subject: [PATCH] better generics

---
 src/diagnostic.rs | 110 +++++++++++++++++-----------------------------
 src/pointer.rs    |   2 +-
 2 files changed, 42 insertions(+), 70 deletions(-)

diff --git a/src/diagnostic.rs b/src/diagnostic.rs
index f49a6f8..445a8f4 100644
--- a/src/diagnostic.rs
+++ b/src/diagnostic.rs
@@ -8,7 +8,7 @@ pub trait Diagnostic<'s>: Sized + private::Sealed {
     type Subject: private::IntoOwned;
 
     /// Combine the error with its subject to generate a [`Report`].
-    fn into_report(self, subject: impl Into<Self::Subject>) -> Report<'s, Self> {
+    fn into_report(self, subject: impl Into<Self::Subject>) -> Report<Self, Self::Subject> {
         Report::new(self, subject)
     }
 
@@ -42,15 +42,15 @@ impl From<Label> for miette::LabeledSpan {
 }
 
 /// An error wrapper which includes the subject of the failure.
-#[derive(Clone, PartialEq, Eq)]
-pub struct Report<'s, S: Diagnostic<'s>> {
-    source: S,
-    subject: S::Subject,
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Report<SRC, SUB> {
+    source: SRC,
+    subject: SUB,
 }
 
-impl<'s, S: Diagnostic<'s>> Report<'s, S> {
+impl<SRC, SUB> Report<SRC, SUB> {
     /// Create a new `Report` with the given subject and error.
-    fn new(source: S, subject: impl Into<S::Subject>) -> Self {
+    fn new(source: SRC, subject: impl Into<SUB>) -> Self {
         Self {
             source,
             subject: subject.into(),
@@ -58,80 +58,58 @@ impl<'s, S: Diagnostic<'s>> Report<'s, S> {
     }
 
     /// The value which caused the error.
-    pub fn subject(&self) -> &S::Subject {
+    pub fn subject(&self) -> &SUB {
         &self.subject
     }
 
     /// The error which occurred.
-    pub fn original(&self) -> &S {
+    pub fn original(&self) -> &SRC {
         &self.source
     }
 
     /// The original parts of the [`Report`].
-    pub fn decompose(self) -> (S, S::Subject) {
+    pub fn decompose(self) -> (SRC, SUB) {
         (self.source, self.subject)
     }
 }
 
-impl<'s, S> Report<'s, S>
+impl<'s, S> Report<S, <S as Diagnostic<'s>>::Subject>
 where
     S: Diagnostic<'s>,
 {
     /// Converts the Report into an owned instance (generally by cloning the subject).
-    pub fn into_owned<O>(self) -> Report<'static, O>
-    where
-        S: Into<O>,
-        O: Diagnostic<'static, Subject = <S::Subject as private::IntoOwned>::Owned>,
-    {
+    pub fn into_owned(self) -> Report<S, <S::Subject as private::IntoOwned>::Owned> {
         use private::IntoOwned;
 
         Report {
-            // TODO: is there a way to avoid the `Into` here? We really want `S == O`,
-            // but I'm strugggling to express that without a bound predicate cycle
-            source: self.source.into(),
+            source: self.source,
             subject: self.subject.into_owned(),
         }
     }
 }
 
-impl<'s, S> core::ops::Deref for Report<'s, S>
-where
-    S: Diagnostic<'s>,
-{
-    type Target = S;
+impl<SRC, SUB> core::ops::Deref for Report<SRC, SUB> {
+    type Target = SRC;
 
     fn deref(&self) -> &Self::Target {
         &self.source
     }
 }
 
-impl<'s, S> fmt::Display for Report<'s, S>
+impl<SRC, SUB> fmt::Display for Report<SRC, SUB>
 where
-    S: Diagnostic<'s> + fmt::Display,
+    SRC: fmt::Display,
 {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         fmt::Display::fmt(&self.source, f)
     }
 }
 
-impl<'s, S> fmt::Debug for Report<'s, S>
-where
-    S: Diagnostic<'s> + fmt::Debug,
-    S::Subject: fmt::Debug,
-{
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Enriched")
-            .field("source", &self.source)
-            .field("subject", &self.subject)
-            .finish()
-    }
-}
-
 #[cfg(feature = "std")]
-impl<'s, S> std::error::Error for Report<'s, S>
+impl<SRC, SUB> std::error::Error for Report<SRC, SUB>
 where
-    S: Diagnostic<'s> + fmt::Debug + std::error::Error + 'static,
-    S::Subject: fmt::Debug,
+    SRC: fmt::Debug + std::error::Error + 'static,
+    SUB: fmt::Debug,
 {
     fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
         Some(&self.source)
@@ -139,13 +117,13 @@ where
 }
 
 #[cfg(feature = "miette")]
-impl<'s, S> miette::Diagnostic for Report<'s, S>
+impl<'s, SRC> miette::Diagnostic for Report<SRC, SRC::Subject>
 where
-    S: Diagnostic<'s> + fmt::Debug + std::error::Error + 'static,
-    S::Subject: fmt::Debug + miette::SourceCode,
+    SRC: Diagnostic<'s> + fmt::Debug + std::error::Error + 'static,
+    SRC::Subject: fmt::Debug + miette::SourceCode,
 {
     fn url<'a>(&'a self) -> Option<Box<dyn core::fmt::Display + 'a>> {
-        Some(Box::new(S::url()))
+        Some(Box::new(SRC::url()))
     }
 
     fn source_code(&self) -> Option<&dyn miette::SourceCode> {
@@ -153,7 +131,7 @@ where
     }
 
     fn labels(&self) -> Option<Box<dyn Iterator<Item = miette::LabeledSpan> + '_>> {
-        Some(Box::new(S::labels(self, &self.subject)?.map(Into::into)))
+        Some(Box::new(SRC::labels(self, &self.subject)?.map(Into::into)))
     }
 }
 
@@ -187,7 +165,6 @@ macro_rules! impl_diagnostic_url {
 pub(crate) use impl_diagnostic_url;
 
 mod private {
-    use crate::Pointer;
     use alloc::borrow::Cow;
 
     pub trait Sealed {}
@@ -195,23 +172,15 @@ mod private {
     impl Sealed for crate::assign::Error {}
 
     pub trait IntoOwned {
-        type Owned: 'static;
+        type Owned;
 
         fn into_owned(self) -> Self::Owned;
     }
 
-    impl<'s> IntoOwned for Cow<'s, str> {
-        type Owned = Cow<'static, str>;
-
-        fn into_owned(self) -> Cow<'static, str> {
-            Cow::Owned(self.into_owned())
-        }
-    }
-
-    impl<'s> IntoOwned for Cow<'s, Pointer> {
-        type Owned = Cow<'static, Pointer>;
+    impl<'s, T: 'static + ToOwned + ?Sized> IntoOwned for Cow<'s, T> {
+        type Owned = Cow<'static, T>;
 
-        fn into_owned(self) -> Cow<'static, Pointer> {
+        fn into_owned(self) -> Cow<'static, T> {
             Cow::Owned(self.into_owned())
         }
     }
@@ -224,10 +193,13 @@ pub trait Diagnose<'s, T> {
     fn diagnose(
         self,
         subject: impl Into<<Self::Error as Diagnostic<'s>>::Subject>,
-    ) -> Result<T, Report<'s, Self::Error>>;
+    ) -> Result<T, Report<Self::Error, <Self::Error as Diagnostic<'s>>::Subject>>;
 
     #[allow(clippy::missing_errors_doc)]
-    fn diagnose_with<F, S>(self, f: F) -> Result<T, Report<'s, Self::Error>>
+    fn diagnose_with<F, S>(
+        self,
+        f: F,
+    ) -> Result<T, Report<Self::Error, <Self::Error as Diagnostic<'s>>::Subject>>
     where
         F: FnOnce() -> S,
         S: Into<<Self::Error as Diagnostic<'s>>::Subject>;
@@ -242,11 +214,14 @@ where
     fn diagnose(
         self,
         subject: impl Into<<Self::Error as Diagnostic<'s>>::Subject>,
-    ) -> Result<T, Report<'s, Self::Error>> {
+    ) -> Result<T, Report<Self::Error, <Self::Error as Diagnostic<'s>>::Subject>> {
         self.map_err(|error| error.into_report(subject.into()))
     }
 
-    fn diagnose_with<F, S>(self, f: F) -> Result<T, Report<'s, Self::Error>>
+    fn diagnose_with<F, S>(
+        self,
+        f: F,
+    ) -> Result<T, Report<Self::Error, <Self::Error as Diagnostic<'s>>::Subject>>
     where
         F: FnOnce() -> S,
         S: Into<<Self::Error as Diagnostic<'s>>::Subject>,
@@ -258,7 +233,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{ParseError, Pointer, PointerBuf};
+    use crate::{Pointer, PointerBuf};
 
     #[test]
     #[cfg(all(
@@ -294,10 +269,7 @@ mod tests {
 
     #[test]
     fn into_owned() {
-        // NOTE: the type has to be fully specified here because of the `S: Into<O>` bound
-        // in `Report::into_owned`. Ideally we'd express `S == O` so that the output can
-        // be automatically inferred.
-        let owned_report: Report<'static, ParseError> = {
+        let owned_report = {
             // creating owned string to ensure its lifetime is local
             // (could also coerce a static reference, but this is less brittle)
             let invalid = "/foo/bar/invalid~3~encoding/cannot/reach".to_string();
diff --git a/src/pointer.rs b/src/pointer.rs
index 90a882e..8861913 100644
--- a/src/pointer.rs
+++ b/src/pointer.rs
@@ -1387,7 +1387,7 @@ impl std::error::Error for ParseError {
     }
 }
 
-pub type RichParseError<'s> = Report<'s, ParseError>;
+pub type RichParseError<'s> = Report<ParseError, <ParseError as Diagnostic<'s>>::Subject>;
 
 /*
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