Address review comments

src/librustc_typeck/check/cast.rs

@@ -115,12 +115,12 @@ pub fn check_cast<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>, cast: &CastCheck<'tcx>) {
     } else if t_1.sty == ty::ty_bool {
         span_err!(fcx.tcx().sess, span, E0054,
                   "cannot cast as `bool`, compare with zero instead");
-    } else if t_e_is_float && (t_1_is_scalar || t_1_is_c_enum) && !(
-        t_1_is_integral || t_1_is_float) {
+    } else if t_e_is_float && (t_1_is_scalar || t_1_is_c_enum) &&
+        !(t_1_is_integral || t_1_is_float) {
         // Casts from float must go through an integer
         cast_through_integer_err(fcx, span, t_1, t_e)
-    } else if t_1_is_float && (t_e_is_scalar || t_e_is_c_enum) && !(
-        t_e_is_integral || t_e_is_float || t_e.sty == ty::ty_bool) {
+    } else if t_1_is_float && (t_e_is_scalar || t_e_is_c_enum) &&
+        !(t_e_is_integral || t_e_is_float || t_e.sty == ty::ty_bool) {
         // Casts to float must go through an integer or boolean
         cast_through_integer_err(fcx, span, t_1, t_e)
     } else if t_e_is_c_enum && t_1_is_trivial {

src/librustc_typeck/check/mod.rs

@@ -1560,13 +1560,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     pub fn type_is_fat_ptr(&self, ty: Ty<'tcx>, span: Span) -> bool {
-        match ty.sty {
-            ty::ty_ptr(ty::mt { ty: t, .. }) |
-            ty::ty_rptr(_, ty::mt { ty: t, .. }) => {
-                !self.type_is_known_to_be_sized(t, span)
-            }
-            _ => false
+        if let Some(mt) = ty::deref(ty, true) {
+            return !self.type_is_known_to_be_sized(mt.ty, span);
         }
+        false
     }
 
     pub fn register_builtin_bound(&self,

src/test/compile-fail/fat-ptr-cast.rs

@@ -10,5 +10,10 @@
 
 fn main() {
     let a: &[i32] = &[1, 2, 3];
-    a as *const [i32] as usize; //~ ERROR cast from fat pointer
+    let b: Box<[i32]> = Box::new([1, 2, 3]);
+    let p = a as *const [i32];
+
+    a as usize; //~ ERROR cast from fat pointer
+    b as usize; //~ ERROR cast from fat pointer
+    p as usize; //~ ERROR cast from fat pointer
 }