update for enum discriminant changes

Author: RalfJung

src/intrinsic.rs

@@ -198,7 +198,7 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for EvalContext<'a, 'mir, 'tcx, super:
 
             "discriminant_value" => {
                 let place = self.ref_to_mplace(self.read_value(args[0])?)?;
-                let discr_val = self.read_discriminant_value(place.into())?;
+                let discr_val = self.read_discriminant(place.into())?.0;
                 self.write_scalar(Scalar::from_uint(discr_val, dest.layout.size), dest)?;
             }
 

tests/compile-fail/invalid_enum_discriminant.rs

@@ -8,11 +8,10 @@ pub enum Foo {
 
 fn main() {
     let f = unsafe { std::mem::transmute::<i32, Foo>(42) };
-    match f {
+    match f { //~ ERROR invalid enum discriminant
         Foo::A => {},
         Foo::B => {},
         Foo::C => {},
         Foo::D => {},
     }
-} //~ ERROR constant evaluation error
-//~^ NOTE entered unreachable code
+}

tests/compile-fail/invalid_enum_discriminant2.rs

@@ -0,0 +1,16 @@
+// Validation makes this fail in the wrong place
+// compile-flags: -Zmir-emit-validate=0
+
+// error-pattern: invalid enum discriminant
+
+use std::mem;
+
+#[repr(C)]
+pub enum Foo {
+    A, B, C, D
+}
+
+fn main() {
+    let f = unsafe { std::mem::transmute::<i32, Foo>(42) };
+    let _ = mem::discriminant(&f);
+}