Fix derive(Error) expansion hygiene (#527, #526)

- rename `as_dyn_error()` method of `derive_more::__private::AsDynError` trait to `__derive_more_as_dyn_error()` to omit possible ambiguities
- replace `vendor::thiserror::aserror` module with `as_dyn_error` module in `derive_more` crate

Co-authored-by: Kai Ren <tyranron@gmail.com>

Author: AlphaKeks

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## master
+
+### Fixed
+
+- `.as_dyn_error()` method hygiene inside `Error` derive expansion.
+  ([#527](https://github.com/JelteF/derive_more/pull/527))
+
 ## 2.1.0 - 2025-12-02
 
 ### Added

impl/src/error.rs

@@ -287,7 +287,7 @@ fn render_some(mut expr: TokenStream, unpack: bool) -> TokenStream {
     if unpack {
         expr = quote! { derive_more::core::option::Option::as_ref(#expr)? }
     }
-    quote! { Some(#expr.as_dyn_error()) }
+    quote! { Some(#expr.__derive_more_as_dyn_error()) }
 }
 
 fn parse_fields<'input, 'state>(

src/as_dyn_error.rs

@@ -0,0 +1,65 @@
+//! Coercion into `dyn `[`Error`] used in macro expansions.
+//!
+//! # Credits
+//!
+//! The initial idea and implementation was taken from the [`thiserror`] crate and its
+//! [`AsDynError`] trait implementation, and slightly modified for usage in derive [`derive_more`].
+//!
+//! The original code was dual licensed under [Apache License, Version 2.0][APACHE] and [MIT]
+//! licenses.
+//!
+//! [`AsDynError`]: https://github.com/dtolnay/thiserror/blob/2.0.3/src/aserror.rs
+//! [`derive_more`]: crate
+//! [`thiserror`]: https://github.com/dtolnay/thiserror/blob/2.0.3
+//! [APACHE]: https://github.com/dtolnay/thiserror/blob/2.0.3/LICENSE-APACHE
+//! [MIT]: https://github.com/dtolnay/thiserror/blob/2.0.3/LICENSE-MIT
+
+use core::{error::Error, panic::UnwindSafe};
+
+#[doc(hidden)]
+pub trait AsDynError<'a>: Sealed {
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a);
+}
+
+impl<'a, T: Error + 'a> AsDynError<'a> for T {
+    #[inline]
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a) {
+        self
+    }
+}
+
+impl<'a> AsDynError<'a> for dyn Error + 'a {
+    #[inline]
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a) {
+        self
+    }
+}
+
+impl<'a> AsDynError<'a> for dyn Error + Send + 'a {
+    #[inline]
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a) {
+        self
+    }
+}
+
+impl<'a> AsDynError<'a> for dyn Error + Send + Sync + 'a {
+    #[inline]
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a) {
+        self
+    }
+}
+
+impl<'a> AsDynError<'a> for dyn Error + Send + Sync + UnwindSafe + 'a {
+    #[inline]
+    fn __derive_more_as_dyn_error(&self) -> &(dyn Error + 'a) {
+        self
+    }
+}
+
+#[doc(hidden)]
+pub trait Sealed {}
+impl<T: Error> Sealed for T {}
+impl Sealed for dyn Error + '_ {}
+impl Sealed for dyn Error + Send + '_ {}
+impl Sealed for dyn Error + Send + Sync + '_ {}
+impl Sealed for dyn Error + Send + Sync + UnwindSafe + '_ {}

src/lib.rs

@@ -68,7 +68,7 @@ pub mod __private {
     pub use crate::cmp::AssertParamIsEq;
 
     #[cfg(feature = "error")]
-    pub use crate::vendor::thiserror::aserror::AsDynError;
+    pub use crate::as_dyn_error::AsDynError;
 }
 
 // The modules containing error types and other helpers.
@@ -93,7 +93,7 @@ mod r#as;
 mod fmt;
 
 #[cfg(feature = "error")]
-mod vendor;
+mod as_dyn_error;
 
 #[cfg(feature = "from_str")]
 mod r#str;