Delay a bug on non-ADT field access to prevent ICEs on const eval fails in tys

Author: fmease

compiler/rustc_passes/src/dead.rs

@@ -142,7 +142,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                 self.insert_def_id(def.non_enum_variant().fields[index].did);
             }
             ty::Tuple(..) => {}
-            _ => span_bug!(lhs.span, "named field access on non-ADT"),
+            ty => {
+                self.tcx
+                    .dcx()
+                    .span_delayed_bug(lhs.span, format!("named field access on non-ADT `{ty:?}`"));
+            }
         }
     }
 

tests/ui/consts/const-eval/field-access-after-const-eval-fail-in-ty.rs

@@ -0,0 +1,5 @@
+// Regression test for issue #120615.
+
+fn main() {
+    [(); loop {}].field; //~ ERROR constant evaluation is taking a long time
+}

tests/ui/consts/const-eval/field-access-after-const-eval-fail-in-ty.stderr

@@ -0,0 +1,17 @@
+error: constant evaluation is taking a long time
+  --> $DIR/field-access-after-const-eval-fail-in-ty.rs:4:10
+   |
+LL |     [(); loop {}].field;
+   |          ^^^^^^^
+   |
+   = note: this lint makes sure the compiler doesn't get stuck due to infinite loops in const eval.
+           If your compilation actually takes a long time, you can safely allow the lint.
+help: the constant being evaluated
+  --> $DIR/field-access-after-const-eval-fail-in-ty.rs:4:10
+   |
+LL |     [(); loop {}].field;
+   |          ^^^^^^^
+   = note: `#[deny(long_running_const_eval)]` on by default
+
+error: aborting due to 1 previous error
+