Add "type_name" support in emulate_intrinsic()

src/librustc_mir/interpret/intrinsics.rs

@@ -7,7 +7,7 @@ use rustc::ty;
 use rustc::ty::layout::{LayoutOf, Primitive, Size};
 use rustc::mir::BinOp;
 use rustc::mir::interpret::{
-    EvalResult, InterpError, Scalar,
+    EvalResult, InterpError, Scalar, ConstValue
 };
 
 use super::{
@@ -78,6 +78,25 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, 'mir, 'tcx, M>
                 let id_val = Scalar::from_uint(type_id, dest.layout.size);
                 self.write_scalar(id_val, dest)?;
             }
+
+            "type_name" => {
+                let const_val = type_name(self.tcx.tcx, substs.type_at(0)).val;
+                if let ConstValue::Slice {
+                    data: slice_val,
+                    start: _,
+                    end: _,
+                } = const_val
+                {
+                    // unsafe for from_utf8_unchecked()
+                    unsafe {
+                        let str_val = core::str::from_utf8_unchecked(&slice_val.bytes);
+                        let name_val = self.str_to_immediate(str_val)?;
+                        self.write_immediate(name_val, dest)?;
+                    }
+                } else {
+                    bug!("type_name() somehow failed to return a ConstValue::Slice");
+                }
+            }
             | "ctpop"
             | "cttz"
             | "cttz_nonzero"

src/test/run-pass/ctfe/const-fn-type-name.rs

@@ -0,0 +1,37 @@
+// run-pass
+
+#![feature(core_intrinsics)]
+#![feature(const_fn)]
+#![allow(dead_code)]
+
+const fn type_name_wrapper<T>(_: &T) -> &'static str {
+    unsafe { core::intrinsics::type_name::<T>() }
+}
+
+struct Struct<TA, TB, TC> {
+    a: TA,
+    b: TB,
+    c: TC,
+}
+
+type StructInstantiation = Struct<i8, f64, bool>;
+
+const CONST_STRUCT: StructInstantiation = StructInstantiation {
+    a: 12,
+    b: 13.7,
+    c: false,
+};
+
+const CONST_STRUCT_NAME: &'static str = type_name_wrapper(&CONST_STRUCT);
+
+fn main() {
+    let non_const_struct = StructInstantiation {
+        a: 87,
+        b: 65.99,
+        c: true,
+    };
+
+    let non_const_struct_name = type_name_wrapper(&non_const_struct);
+
+    assert_eq!(CONST_STRUCT_NAME, non_const_struct_name);
+}