Auto merge of #1032 - RalfJung:offset-from, r=RalfJung

test offset_from

This currently fails and needs a rustc fix: https://github.com/rust-lang/rust/pull/66083

rust-version

@@ -1 +1 @@
-6c1b220fd747bf244f04b380e4d4ae005068f706
+3a1b3b30c6cdd674049b144a3ced7b711de962b2

tests/run-pass/ptr_offset_from.rs

@@ -0,0 +1,29 @@
+#![feature(ptr_offset_from)]
+
+fn test_raw() { unsafe {
+    let buf = [0u32; 4];
+
+    let x = buf.as_ptr() as *const u8;
+    let y = x.offset(12);
+
+    assert_eq!(y.offset_from(x), 12);
+    assert_eq!(x.offset_from(y), -12);
+    assert_eq!((y as *const u32).offset_from(x as *const u32), 12/4);
+    assert_eq!((x as *const u32).offset_from(y as *const u32), -12/4);
+    
+    let x = (((x as usize) * 2) / 2) as *const u8;
+    assert_eq!(y.offset_from(x), 12);
+    assert_eq!(x.offset_from(y), -12);
+} }
+
+// This also internally uses offset_from.
+fn test_vec_into_iter() {
+    let v = Vec::<i32>::new();
+    let i = v.into_iter();
+    i.size_hint();
+}
+
+fn main() {
+    test_raw();
+    test_vec_into_iter();
+}