1 files changed, 24 insertions, 0 deletions
diff --git a/tests/ui/consts/const-eval/transmute-size-mismatch.rs b/tests/ui/consts/const-eval/transmute-size-mismatch.rs
new file mode 100644
index 000000000..2410baea2
--- /dev/null
+++ b/tests/ui/consts/const-eval/transmute-size-mismatch.rs
@@ -0,0 +1,24 @@
+#![feature(core_intrinsics)]
+#![feature(custom_mir)]
+
+// These cases are statically rejected by `mem::transmute`, so we need custom
+// MIR to be able to get to constant evaluation.
+use std::intrinsics::mir::*;
+
+#[custom_mir(dialect = "runtime", phase = "initial")]
+const unsafe fn mir_transmute<T, U>(x: T) -> U {
+    mir!{
+        {
+            RET = CastTransmute(x);
+            //~^ ERROR evaluation of constant value failed
+            //~| ERROR evaluation of constant value failed
+            Return()
+        }
+    }
+}
+
+const FROM_BIGGER: u16 = unsafe { mir_transmute(123_i32) };
+
+const FROM_SMALLER: u32 = unsafe { mir_transmute(123_i16) };
+
+fn main() {}