From 2159eaf5789c8c367e4c7f77c62d79262ea0252e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maja=20K=C4=85dzio=C5=82ka?= <maya@compilercrim.es>
Date: Sun, 4 Jan 2026 23:37:32 +0100
Subject: [PATCH] Add a validity testcase for uninhabited variants

---
 .../tests/fail/validity/uninhabited_variant.rs  | 17 +++++++++++++++++
 .../fail/validity/uninhabited_variant.stderr    | 13 +++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 src/tools/miri/tests/fail/validity/uninhabited_variant.rs
 create mode 100644 src/tools/miri/tests/fail/validity/uninhabited_variant.stderr

diff --git a/src/tools/miri/tests/fail/validity/uninhabited_variant.rs b/src/tools/miri/tests/fail/validity/uninhabited_variant.rs
new file mode 100644
index 000000000000..303584423fdc
--- /dev/null
+++ b/src/tools/miri/tests/fail/validity/uninhabited_variant.rs
@@ -0,0 +1,17 @@
+// NOTE: this is essentially a smoke-test, with more comprehensive tests living in the rustc
+// repository at tests/ui/consts/const-eval/ub-enum.rs
+#![feature(never_type)]
+
+#[repr(C)]
+#[allow(dead_code)]
+enum E {
+    V1,    // discriminant: 0
+    V2(!), // 1
+}
+
+fn main() {
+    unsafe {
+        std::mem::transmute::<u32, E>(1);
+        //~^ ERROR: encountered an uninhabited enum variant
+    }
+}
diff --git a/src/tools/miri/tests/fail/validity/uninhabited_variant.stderr b/src/tools/miri/tests/fail/validity/uninhabited_variant.stderr
new file mode 100644
index 000000000000..76ee25009b6e
--- /dev/null
+++ b/src/tools/miri/tests/fail/validity/uninhabited_variant.stderr
@@ -0,0 +1,13 @@
+error: Undefined Behavior: constructing invalid value at .<enum-tag>: encountered an uninhabited enum variant
+  --> tests/fail/validity/uninhabited_variant.rs:LL:CC
+   |
+LL |         std::mem::transmute::<u32, E>(1);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+