Implement unsize of adt's (cc rust-lang#14)

Author: bjorn3

examples/mini_core.rs

@@ -12,6 +12,7 @@ pub trait Unsize<T: ?Sized> {}
 pub trait CoerceUnsized<T> {}
 
 impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
 
 #[lang = "copy"]
 pub unsafe trait Copy {}
@@ -203,7 +204,9 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
 }
 
 #[lang = "owned_box"]
-pub struct Box<T>(*mut T);
+pub struct Box<T: ?Sized>(*mut T);
+
+impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}
 
 static mut MY_TINY_HEAP: [u8; 16] = [0; 16];
 

examples/mini_core_hello_world.rs

@@ -111,8 +111,9 @@ fn main() {
         // TODO remove when jit supports linking rlibs
         #[cfg(not(jit))]
         {
-            let world = box "World!\0";
+            let world: Box<&str> = box "World!\0";
             puts(*world as *const str as *const u8);
+            world as Box<SomeTrait>;
         }
 
         assert_eq!(intrinsics::size_of_val(hello) as u8, 6);

src/common.rs

@@ -252,7 +252,22 @@ impl<'tcx> CValue<'tcx> {
                 };
                 dest.write_cvalue(fx, CValue::ByValPair(ptr, extra, dest.layout()));
             }
-            ty => unimpl!("unsize of non ptr {:?}", ty),
+            _ => {
+                assert!(!self.layout().ty.is_enum(), "Tried to unsize enum");
+                let field_count = self.layout().fields.count();
+                let mut found_unsize_field = false;
+                for idx in 0..field_count {
+                    let field_dest = dest.place_field(fx, mir::Field::new(idx));
+                    let field_src = self.value_field(fx, mir::Field::new(idx));
+                    if field_src.layout().ty != field_dest.layout().ty {
+                        assert!(!found_unsize_field);
+                        found_unsize_field = true;
+                        field_src.unsize_value(fx, field_dest);
+                    } else {
+                        field_dest.write_cvalue(fx, field_src);
+                    }
+                }
+            }
         }
     }