Rewrite the intrinsicck to take the parameter environment into account. Also fixes #20116.

src/test/compile-fail/transmute-different-sizes.rs

@@ -21,7 +21,7 @@ unsafe fn f() {
 
 unsafe fn g<T>(x: &T) {
     let _: i8 = transmute(x);
-    //~^ ERROR transmute called on types with different sizes
+    //~^ ERROR transmute called on types with potentially different sizes
 }
 
 fn main() {}

src/test/compile-fail/transmute-fat-pointers.rs

@@ -0,0 +1,41 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Tests that are conservative around thin/fat pointer mismatches.
+
+#![allow(dead_code)]
+
+use std::mem::transmute;
+
+fn a<T, Sized? U>(x: &[T]) -> &U {
+    unsafe { transmute(x) } //~ ERROR transmute called on types with potentially different sizes
+}
+
+fn b<Sized? T, Sized? U>(x: &T) -> &U {
+    unsafe { transmute(x) } //~ ERROR transmute called on types with potentially different sizes
+}
+
+fn c<T, U>(x: &T) -> &U {
+    unsafe { transmute(x) }
+}
+
+fn d<T, U>(x: &[T]) -> &[U] {
+    unsafe { transmute(x) }
+}
+
+fn e<Sized? T, U>(x: &T) -> &U {
+    unsafe { transmute(x) } //~ ERROR transmute called on types with potentially different sizes
+}
+
+fn f<T, Sized? U>(x: &T) -> &U {
+    unsafe { transmute(x) } //~ ERROR transmute called on types with potentially different sizes
+}
+
+fn main() { }

src/test/compile-fail/transmute-impl.rs

@@ -0,0 +1,33 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Tests that are conservative around thin/fat pointer mismatches.
+
+#![allow(dead_code)]
+
+use std::mem::transmute;
+
+struct Foo<Sized? T> {
+    t: Box<T>
+}
+
+impl<Sized? T> Foo<T> {
+    fn m(x: &T) -> &int where T : Sized {
+        // OK here, because T : Sized is in scope.
+        unsafe { transmute(x) }
+    }
+
+    fn n(x: &T) -> &int {
+        // Not OK here, because T : Sized is not in scope.
+        unsafe { transmute(x) } //~ ERROR transmute called on types with potentially different sizes
+    }
+}
+
+fn main() { }