Add regression tests

tests/ui/consts/erroneous_type_in_promoted.rs

@@ -0,0 +1,14 @@
+//! ICE test #124348
+//! We should not be running const eval if the layout has errors.
+
+enum Eek {
+    TheConst,
+    UnusedByTheConst(Sum),
+    //~^ ERROR cannot find type `Sum` in this scope
+}
+
+const fn foo() {
+    let x: &'static [Eek] = &[];
+}
+
+fn main() {}

tests/ui/consts/erroneous_type_in_promoted.stderr

@@ -0,0 +1,28 @@
+error[E0412]: cannot find type `Sum` in this scope
+  --> $DIR/erroneous_type_in_promoted.rs:6:22
+   |
+LL |     UnusedByTheConst(Sum),
+   |                      ^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL + use std::iter::Sum;
+   |
+
+note: erroneous constant encountered
+  --> $DIR/erroneous_type_in_promoted.rs:11:29
+   |
+LL |     let x: &'static [Eek] = &[];
+   |                             ^^^
+
+note: erroneous constant encountered
+  --> $DIR/erroneous_type_in_promoted.rs:11:29
+   |
+LL |     let x: &'static [Eek] = &[];
+   |                             ^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0412`.