Auto merge of rust-lang#34879 - petrochenkov:fnptr, r=alexcrichton

Implement traits for variadic function pointers

Closes rust-lang#34874
cc rust-lang#28268

r? @alexcrichton

Author: bors

src/libcore/ptr.rs

@@ -571,12 +571,21 @@ macro_rules! fnptr_impls_safety_abi {
 }
 
 macro_rules! fnptr_impls_args {
-    ($($Arg: ident),*) => {
+    ($($Arg: ident),+) => {
         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! { 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),* }
+    };
+    () => {
+        // 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! { unsafe extern "Rust" fn() -> Ret, }
+        fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, }
+    };
 }
 
 fnptr_impls_args! { }

src/libcoretest/ptr.rs

@@ -171,3 +171,17 @@ fn test_unsized_unique() {
     let zs: &mut [i32] = &mut [1, 2, 3];
     assert!(ys == zs);
 }
+
+#[test]
+fn test_variadic_fnptr() {
+    use core::hash::{Hash, SipHasher};
+    extern "C" {
+        fn printf(_: *const u8, ...);
+    }
+    let p: unsafe extern "C" fn(*const u8, ...) = printf;
+    let q = p.clone();
+    assert_eq!(p, q);
+    assert!(!(p < q));
+    let mut s = SipHasher::new();
+    assert_eq!(p.hash(&mut s), q.hash(&mut s));
+}