Auto merge of #103279 - compiler-errors:normalize-hack-back, r=lcnr

Add eval hack in `super_relate_consts` back

Partially reverts 01adb7e98d5656c06497f33dd2747df144e78356.

This extra eval call *still* needs to happen, for example, in `normalize_param_env_or_error` when a param-env predicate has an unnormalized constant, since the param-env candidates never get normalized during candidate assembly (everywhere else we can assume that they are normalized fully).

r? `@lcnr,` though I feel like I've assigned quite a few PRs to you in the last few days, so feel free to reassign to someone else familiar with this code if you're busy!

cc #103243 (fixes the issue, but don't want to auto-close that until a backport is performed).

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -554,6 +554,13 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         val: &mir::ConstantKind<'tcx>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
+        // FIXME(const_prop): normalization needed b/c const prop lint in
+        // `mir_drops_elaborated_and_const_checked`, which happens before
+        // optimized MIR. Only after optimizing the MIR can we guarantee
+        // that the `RevealAll` pass has happened and that the body's consts
+        // are normalized, so any call to resolve before that needs to be
+        // manually normalized.
+        let val = self.tcx.normalize_erasing_regions(self.param_env, *val);
         match val {
             mir::ConstantKind::Ty(ct) => {
                 match ct.kind() {
@@ -585,7 +592,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     }
                 }
             }
-            mir::ConstantKind::Val(val, ty) => self.const_val_to_op(*val, *ty, layout),
+            mir::ConstantKind::Val(val, ty) => self.const_val_to_op(val, ty, layout),
             mir::ConstantKind::Unevaluated(uv, _) => {
                 let instance = self.resolve(uv.def, uv.substs)?;
                 Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())

compiler/rustc_middle/src/ty/relate.rs

@@ -574,8 +574,8 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
 /// it.
 pub fn super_relate_consts<'tcx, R: TypeRelation<'tcx>>(
     relation: &mut R,
-    a: ty::Const<'tcx>,
-    b: ty::Const<'tcx>,
+    mut a: ty::Const<'tcx>,
+    mut b: ty::Const<'tcx>,
 ) -> RelateResult<'tcx, ty::Const<'tcx>> {
     debug!("{}.super_relate_consts(a = {:?}, b = {:?})", relation.tag(), a, b);
     let tcx = relation.tcx();
@@ -596,6 +596,17 @@ pub fn super_relate_consts<'tcx, R: TypeRelation<'tcx>>(
         );
     }
 
+    // HACK(const_generics): We still need to eagerly evaluate consts when
+    // relating them because during `normalize_param_env_or_error`,
+    // we may relate an evaluated constant in a obligation against
+    // an unnormalized (i.e. unevaluated) const in the param-env.
+    // FIXME(generic_const_exprs): Once we always lazily unify unevaluated constants
+    // these `eval` calls can be removed.
+    if !relation.tcx().features().generic_const_exprs {
+        a = a.eval(tcx, relation.param_env());
+        b = b.eval(tcx, relation.param_env());
+    }
+
     // Currently, the values that can be unified are primitive types,
     // and those that derive both `PartialEq` and `Eq`, corresponding
     // to structural-match types.

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -483,7 +483,12 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         // Use `Reveal::All` here because patterns are always monomorphic even if their function
         // isn't.
         let param_env_reveal_all = self.param_env.with_reveal_all_normalized(self.tcx);
-        let substs = self.typeck_results.node_substs(id);
+        // N.B. There is no guarantee that substs collected in typeck results are fully normalized,
+        // so they need to be normalized in order to pass to `Instance::resolve`, which will ICE
+        // if given unnormalized types.
+        let substs = self
+            .tcx
+            .normalize_erasing_regions(param_env_reveal_all, self.typeck_results.node_substs(id));
         let instance = match ty::Instance::resolve(self.tcx, param_env_reveal_all, def_id, substs) {
             Ok(Some(i)) => i,
             Ok(None) => {

src/test/ui/consts/unnormalized-param-env.rs

@@ -0,0 +1,31 @@
+// check-pass
+
+pub trait CSpace<const N: usize> {
+    type Traj;
+}
+
+pub struct Const<const R: usize>;
+
+pub trait Obstacle<CS, const N: usize> {
+    fn trajectory_free<FT, S1>(&self, t: &FT)
+    where
+        CS::Traj: Sized,
+        CS: CSpace<N>;
+}
+
+// -----
+
+const N: usize = 4;
+
+struct ObstacleSpace2df32;
+
+impl<CS> Obstacle<CS, N> for ObstacleSpace2df32 {
+    fn trajectory_free<TF, S1>(&self, t: &TF)
+    where
+        CS::Traj: Sized,
+        CS: CSpace<N>,
+    {
+    }
+}
+
+fn main() {}