Add no_std support

Cargo.toml

@@ -26,3 +26,6 @@ members = ["impl"]
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]
 rustdoc-args = ["--generate-link-to-definition"]
+
+[features]
+no_std = []

impl/src/attr.rs

@@ -197,14 +197,14 @@ impl ToTokens for Display<'_> {
         let fmt = &self.fmt;
         let args = &self.args;
         tokens.extend(quote! {
-            std::write!(__formatter, #fmt #args)
+            ::core::write!(__formatter, #fmt #args)
         });
     }
 }
 
 impl ToTokens for Trait {
     fn to_tokens(&self, tokens: &mut TokenStream) {
         let trait_name = format_ident!("{}", format!("{:?}", self));
-        tokens.extend(quote!(std::fmt::#trait_name));
+        tokens.extend(quote!(::core::fmt::#trait_name));
     }
 }

src/aserror.rs

@@ -1,5 +1,5 @@
-use std::error::Error;
-use std::panic::UnwindSafe;
+use crate::__private::Error;
+use core::panic::UnwindSafe;
 
 pub trait AsDynError<'a>: Sealed {
     fn as_dyn_error(&self) -> &(dyn Error + 'a);

src/display.rs

@@ -1,28 +1,57 @@
-use std::fmt::Display;
-use std::path::{self, Path, PathBuf};
+use core::fmt::Display;
 
-pub trait DisplayAsDisplay {
-    fn as_display(&self) -> Self;
+pub trait AsDisplay {
+    type Target: Display + ?Sized;
+
+    fn as_display(&self) -> &Self::Target;
 }
 
-impl<T: Display> DisplayAsDisplay for &T {
-    fn as_display(&self) -> Self {
+impl<T: Display> AsDisplay for &T {
+    type Target = T;
+
+    fn as_display(&self) -> &Self::Target {
         self
     }
 }
 
-pub trait PathAsDisplay {
-    fn as_display(&self) -> path::Display<'_>;
-}
+#[cfg(not(feature = "no_std"))]
+mod path {
+    use std::path::{Path, PathBuf};
 
-impl PathAsDisplay for Path {
-    fn as_display(&self) -> path::Display<'_> {
-        self.display()
+    impl super::AsDisplay for Path {
+        type Target = PathDisplay;
+
+        #[inline(always)]
+        fn as_display(&self) -> &Self::Target {
+            PathDisplay::new(self)
+        }
+    }
+
+    impl super::AsDisplay for PathBuf {
+        type Target = PathDisplay;
+
+        #[inline(always)]
+        fn as_display(&self) -> &Self::Target {
+            PathDisplay::new(self.as_path())
+        }
+    }
+
+    #[repr(transparent)]
+    pub struct PathDisplay(Path);
+
+    impl PathDisplay {
+        #[inline(always)]
+        fn new(path: &Path) -> &Self {
+            // SAFETY: PathDisplay is repr(transparent) so casting pointers
+            // between it and its payload is safe.
+            unsafe { &*(path as *const Path as *const Self) }
+        }
     }
-}
 
-impl PathAsDisplay for PathBuf {
-    fn as_display(&self) -> path::Display<'_> {
-        self.display()
+    impl core::fmt::Display for PathDisplay {
+        #[inline(always)]
+        fn fmt(&self, fmtr: &mut core::fmt::Formatter) -> core::fmt::Result {
+            self.0.display().fmt(fmtr)
+        }
     }
 }

src/lib.rs

@@ -237,6 +237,8 @@
     clippy::wildcard_imports,
 )]
 #![cfg_attr(provide_any, feature(provide_any))]
+#![cfg_attr(feature = "no_std", feature(error_in_core))]
+#![cfg_attr(feature = "no_std", no_std)]
 
 mod aserror;
 mod display;
@@ -249,7 +251,11 @@ pub use thiserror_impl::*;
 #[doc(hidden)]
 pub mod __private {
     pub use crate::aserror::AsDynError;
-    pub use crate::display::{DisplayAsDisplay, PathAsDisplay};
+    pub use crate::display::AsDisplay;
     #[cfg(provide_any)]
     pub use crate::provide::ThiserrorProvide;
+    #[cfg(feature = "no_std")]
+    pub use core::error::Error;
+    #[cfg(not(feature = "no_std"))]
+    pub use std::error::Error;
 }

src/provide.rs

@@ -1,4 +1,4 @@
-use std::any::{Demand, Provider};
+use core::any::{Demand, Provider};
 
 pub trait ThiserrorProvide: Sealed {
     fn thiserror_provide<'a>(&'a self, demand: &mut Demand<'a>);

tests/ui/no-display.stderr

@@ -9,7 +9,7 @@ error[E0599]: the method `as_display` exists for reference `&NoDisplay`, but its
   |
   = note: the following trait bounds were not satisfied:
           `NoDisplay: std::fmt::Display`
-          which is required by `&NoDisplay: DisplayAsDisplay`
+          which is required by `&NoDisplay: AsDisplay`
 note: the trait `std::fmt::Display` must be implemented
  --> $RUST/core/src/fmt/mod.rs
   |