Auto merge of #101263 - lopopolo:lopopolo/c-unwind-fn-ptr-impls, r=thomcc

Add default trait implementations for "c-unwind" ABI function pointers

Following up on #92964, only add default trait implementations for the `c-unwind` family of function pointers. The previous attempt in #92964 added trait implementations for many more ABIs and ran into concerns regarding the increase in size of the libcore rlib.

An attempt to abstract away function pointer types behind a unified trait to reduce the duplication of trait impls is being discussed in #99531 but this change looks to be blocked on a lang MCP.

Following `@RalfJung's` suggestion in https://github.com/rust-lang/rust/pull/99531#issuecomment-1233440142, this commit is another cut at #92964 but it _only_ adds the impls for `extern "C-unwind" fn` and `unsafe extern "C-unwind" fn`.

I am interested in landing this patch to unblock the stabilization of the `c_unwind` feature.

RFC: https://github.com/rust-lang/rfcs/pull/2945
Tracking Issue: https://github.com/rust-lang/rust/issues/74990

3 files changed, 23 insertions, 9 deletions

diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 2fd8180f8b2..9cbfbbb9f39 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -174,6 +174,7 @@
 #![feature(allow_internal_unstable)]
 #![feature(associated_type_bounds)]
 #![feature(auto_traits)]
+#![feature(c_unwind)]
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(cfg_target_has_atomic_equal_alignment)]
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 1f7cf6e5d05..8e2bad35993 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -1862,9 +1862,16 @@ macro_rules! maybe_fnptr_doc {
 // Impls for function pointers
 macro_rules! fnptr_impls_safety_abi {
     ($FnTy: ty, $($Arg: ident),*) => {
+        fnptr_impls_safety_abi! { #[stable(feature = "fnptr_impls", since = "1.4.0")] $FnTy, $($Arg),* }
+    };
+    (@c_unwind $FnTy: ty, $($Arg: ident),*) => {
+        #[cfg(not(bootstrap))]
+        fnptr_impls_safety_abi! { #[unstable(feature = "c_unwind", issue = "74990")] $FnTy, $($Arg),* }
+    };
+    (#[$meta:meta] $FnTy: ty, $($Arg: ident),*) => {
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> PartialEq for $FnTy {
                 #[inline]
                 fn eq(&self, other: &Self) -> bool {
@@ -1875,13 +1882,13 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> Eq for $FnTy {}
         }
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> PartialOrd for $FnTy {
                 #[inline]
                 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
@@ -1892,7 +1899,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> Ord for $FnTy {
                 #[inline]
                 fn cmp(&self, other: &Self) -> Ordering {
@@ -1903,7 +1910,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> hash::Hash for $FnTy {
                 fn hash<HH: hash::Hasher>(&self, state: &mut HH) {
                     state.write_usize(*self as usize)
@@ -1913,7 +1920,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> fmt::Pointer for $FnTy {
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     fmt::pointer_fmt_inner(*self as usize, f)
@@ -1923,7 +1930,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> fmt::Debug for $FnTy {
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     fmt::pointer_fmt_inner(*self as usize, f)
@@ -1938,16 +1945,22 @@ macro_rules! fnptr_impls_args {
         fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
     };
     () => {
         // No variadic functions with 0 parameters
         fnptr_impls_safety_abi! { extern "Rust" fn() -> Ret, }
         fnptr_impls_safety_abi! { extern "C" fn() -> Ret, }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn() -> Ret, }
         fnptr_impls_safety_abi! { unsafe extern "Rust" fn() -> Ret, }
         fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn() -> Ret, }
     };
 }
 
diff --git a/src/test/ui/issues/issue-59488.stderr b/src/test/ui/issues/issue-59488.stderr
index 08fe0b35eb7..f9846b62a72 100644
--- a/src/test/ui/issues/issue-59488.stderr
+++ b/src/test/ui/issues/issue-59488.stderr
@@ -99,7 +99,7 @@ LL |     assert_eq!(Foo::Bar, i);
              extern "C" fn(A, B, C, D) -> Ret
              extern "C" fn(A, B, C, D, ...) -> Ret
              extern "C" fn(A, B, C, D, E) -> Ret
-           and 68 others
+           and 118 others
    = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: `fn(usize) -> Foo {Foo::Bar}` doesn't implement `Debug`
@@ -118,7 +118,7 @@ LL |     assert_eq!(Foo::Bar, i);
              extern "C" fn(A, B, C, D) -> Ret
              extern "C" fn(A, B, C, D, ...) -> Ret
              extern "C" fn(A, B, C, D, E) -> Ret
-           and 68 others
+           and 118 others
    = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 10 previous errors