Rollup merge of rust-lang#55474 - oli-obk:const_eval_promoted, r=RalfJung

Fix validation false positive

Fixes rust-lang#55454

r? @RalfJung

Author: kennytm

src/librustc_mir/const_eval.rs

@@ -576,7 +576,11 @@ pub fn const_eval_provider<'a, 'tcx>(
         key.param_env.reveal = Reveal::UserFacing;
         match tcx.const_eval(key) {
             // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric) => {},
+            Err(ErrorHandled::TooGeneric) => {
+                // Promoteds should never be "too generic" when getting evaluated.
+                // They either don't get evaluated, or we are in a monomorphic context
+                assert!(key.value.promoted.is_none());
+            },
             // dedupliate calls
             other => return other,
         }

src/librustc_mir/interpret/validity.rs

@@ -303,7 +303,8 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
         let (lo, hi) = layout.valid_range.clone().into_inner();
         let max_hi = u128::max_value() >> (128 - size.bits()); // as big as the size fits
         assert!(hi <= max_hi);
-        if lo == 0 && hi == max_hi {
+        // We could also write `(hi + 1) % (max_hi + 1) == lo` but `max_hi + 1` overflows for `u128`
+        if (lo == 0 && hi == max_hi) || (hi + 1 == lo) {
             // Nothing to check
             return Ok(());
         }

src/test/ui/consts/const-validation-fail-55455.rs

@@ -0,0 +1,9 @@
+// https://github.com/rust-lang/rust/issues/55454
+// compile-pass
+
+struct This<T>(T);
+
+const C: This<Option<&i32>> = This(Some(&1));
+
+fn main() {
+}

src/test/ui/consts/promoted-validation-55454.rs

@@ -0,0 +1,9 @@
+// https://github.com/rust-lang/rust/issues/55454
+// compile-pass
+
+#[derive(PartialEq)]
+struct This<T>(T);
+
+fn main() {
+    This(Some(&1)) == This(Some(&1));
+}