const_generics: correctly deal with bound variables

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -79,9 +79,9 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
             ty::Projection(_)
             | ty::Opaque(_, _)
             | ty::Param(_)
-            | ty::Bound(_, _)
             | ty::Placeholder(_)
             | ty::Infer(_) => throw_inval!(TooGeneric),
+            ty::Bound(_, _) => bug!("bound ty during ctfe"),
             ty::Bool
             | ty::Char
             | ty::Int(_)

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -559,15 +559,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
         match c.kind() {
-            ty::ConstKind::Param(_) | ty::ConstKind::Bound(..) => throw_inval!(TooGeneric),
+            ty::ConstKind::Param(_) | ty::ConstKind::Placeholder(..) => throw_inval!(TooGeneric),
             ty::ConstKind::Error(DelaySpanBugEmitted { reported, .. }) => {
                 throw_inval!(AlreadyReported(reported))
             }
             ty::ConstKind::Unevaluated(uv) => {
                 let instance = self.resolve(uv.def, uv.substs)?;
                 Ok(self.eval_to_allocation(GlobalId { instance, promoted: uv.promoted })?.into())
             }
-            ty::ConstKind::Infer(..) | ty::ConstKind::Placeholder(..) => {
+            ty::ConstKind::Bound(..) | ty::ConstKind::Infer(..) => {
                 span_bug!(self.cur_span(), "const_to_op: Unexpected ConstKind {:?}", c)
             }
             ty::ConstKind::Value(valtree) => {

compiler/rustc_infer/src/infer/combine.rs

@@ -486,7 +486,7 @@ struct Generalizer<'cx, 'tcx> {
 
     param_env: ty::ParamEnv<'tcx>,
 
-    cache: SsoHashMap<Ty<'tcx>, RelateResult<'tcx, Ty<'tcx>>>,
+    cache: SsoHashMap<Ty<'tcx>, Ty<'tcx>>,
 }
 
 /// Result from a generalization operation. This includes
@@ -593,8 +593,8 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
     fn tys(&mut self, t: Ty<'tcx>, t2: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
         assert_eq!(t, t2); // we are abusing TypeRelation here; both LHS and RHS ought to be ==
 
-        if let Some(result) = self.cache.get(&t) {
-            return result.clone();
+        if let Some(&result) = self.cache.get(&t) {
+            return Ok(result);
         }
         debug!("generalize: t={:?}", t);
 
@@ -664,10 +664,10 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                 Ok(t)
             }
             _ => relate::super_relate_tys(self, t, t),
-        };
+        }?;
 
-        self.cache.insert(t, result.clone());
-        return result;
+        self.cache.insert(t, result);
+        Ok(result)
     }
 
     fn regions(
@@ -743,9 +743,7 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
-                if self.tcx().lazy_normalization() =>
-            {
+            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
                 assert_eq!(promoted, None);
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,
@@ -967,9 +965,7 @@ impl<'tcx> TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
                     }
                 }
             }
-            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
-                if self.tcx().lazy_normalization() =>
-            {
+            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted }) => {
                 assert_eq!(promoted, None);
                 let substs = self.relate_with_variance(
                     ty::Variance::Invariant,

compiler/rustc_middle/src/ty/consts/kind.rs

@@ -180,6 +180,7 @@ impl<'tcx> ConstKind<'tcx> {
         param_env: ParamEnv<'tcx>,
         eval_mode: EvalMode,
     ) -> Option<Result<EvalResult<'tcx>, ErrorGuaranteed>> {
+        assert!(!self.has_escaping_bound_vars(), "escaping vars in {self:?}");
         if let ConstKind::Unevaluated(unevaluated) = self {
             use crate::mir::interpret::ErrorHandled;
 

compiler/rustc_middle/src/ty/relate.rs

@@ -594,10 +594,6 @@ pub fn super_relate_consts<'tcx, R: TypeRelation<'tcx>>(
         );
     }
 
-    let eagerly_eval = |x: ty::Const<'tcx>| x.eval(tcx, relation.param_env());
-    let a = eagerly_eval(a);
-    let b = eagerly_eval(b);
-
     // 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_trait_selection/src/traits/project.rs

@@ -635,13 +635,18 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     fn fold_const(&mut self, constant: ty::Const<'tcx>) -> ty::Const<'tcx> {
-        if self.selcx.tcx().lazy_normalization() || !self.eager_inference_replacement {
+        let tcx = self.selcx.tcx();
+        if tcx.lazy_normalization() {
             constant
         } else {
             let constant = constant.super_fold_with(self);
-            debug!(?constant);
-            debug!("self.param_env: {:?}", self.param_env);
-            constant.eval(self.selcx.tcx(), self.param_env)
+            debug!(?constant, ?self.param_env);
+            with_replaced_escaping_bound_vars(
+                self.selcx.infcx(),
+                &mut self.universes,
+                constant,
+                |constant| constant.eval(tcx, self.param_env),
+            )
         }
     }
 
@@ -671,6 +676,41 @@ pub struct BoundVarReplacer<'me, 'tcx> {
     universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>,
 }
 
+/// Executes `f` on `value` after replacing all escaping bound variables with placeholders
+/// and then replaces these placeholders with the original bound variables in the result.
+///
+/// In most places, bound variables should be replaced right when entering a binder, making
+/// this function unnecessary. However, normalization currently does not do that, so we have
+/// to do this lazily.
+///
+/// You should not add any additional uses of this function, at least not without first
+/// discussing it with t-types.
+///
+/// FIXME(@lcnr): We may even consider experimenting with eagerly replacing bound vars during
+/// normalization as well, at which point this function will be unnecessary and can be removed.
+pub fn with_replaced_escaping_bound_vars<'a, 'tcx, T: TypeFoldable<'tcx>, R: TypeFoldable<'tcx>>(
+    infcx: &'a InferCtxt<'a, 'tcx>,
+    universe_indices: &'a mut Vec<Option<ty::UniverseIndex>>,
+    value: T,
+    f: impl FnOnce(T) -> R,
+) -> R {
+    if value.has_escaping_bound_vars() {
+        let (value, mapped_regions, mapped_types, mapped_consts) =
+            BoundVarReplacer::replace_bound_vars(infcx, universe_indices, value);
+        let result = f(value);
+        PlaceholderReplacer::replace_placeholders(
+            infcx,
+            mapped_regions,
+            mapped_types,
+            mapped_consts,
+            universe_indices,
+            result,
+        )
+    } else {
+        f(value)
+    }
+}
+
 impl<'me, 'tcx> BoundVarReplacer<'me, 'tcx> {
     /// Returns `Some` if we *were* able to replace bound vars. If there are any bound vars that
     /// use a binding level above `universe_indices.len()`, we fail.

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -6,7 +6,7 @@ use crate::infer::at::At;
 use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::{InferCtxt, InferOk};
 use crate::traits::error_reporting::InferCtxtExt;
-use crate::traits::project::needs_normalization;
+use crate::traits::project::{needs_normalization, BoundVarReplacer, PlaceholderReplacer};
 use crate::traits::{Obligation, ObligationCause, PredicateObligation, Reveal};
 use rustc_data_structures::sso::SsoHashMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -283,11 +283,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 let tcx = self.infcx.tcx;
                 let infcx = self.infcx;
                 let (data, mapped_regions, mapped_types, mapped_consts) =
-                    crate::traits::project::BoundVarReplacer::replace_bound_vars(
-                        infcx,
-                        &mut self.universes,
-                        data,
-                    );
+                    BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
                 let data = data.try_fold_with(self)?;
 
                 let mut orig_values = OriginalQueryValues::default();
@@ -313,8 +309,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 debug!("QueryNormalizer: result = {:#?}", result);
                 debug!("QueryNormalizer: obligations = {:#?}", obligations);
                 self.obligations.extend(obligations);
-
-                let res = crate::traits::project::PlaceholderReplacer::replace_placeholders(
+                let res = PlaceholderReplacer::replace_placeholders(
                     infcx,
                     mapped_regions,
                     mapped_types,
@@ -343,7 +338,13 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
         constant: ty::Const<'tcx>,
     ) -> Result<ty::Const<'tcx>, Self::Error> {
         let constant = constant.try_super_fold_with(self)?;
-        Ok(constant.eval(self.infcx.tcx, self.param_env))
+        debug!(?constant, ?self.param_env);
+        Ok(crate::traits::project::with_replaced_escaping_bound_vars(
+            self.infcx,
+            &mut self.universes,
+            constant,
+            |constant| constant.eval(self.infcx.tcx, self.param_env),
+        ))
     }
 
     fn try_fold_mir_const(

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -495,13 +495,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     pub fn to_const(&self, ast_c: &hir::AnonConst) -> ty::Const<'tcx> {
         let const_def_id = self.tcx.hir().local_def_id(ast_c.hir_id);
+        let span = self.tcx.hir().span(ast_c.hir_id);
         let c = ty::Const::from_anon_const(self.tcx, const_def_id);
-        self.register_wf_obligation(
-            c.into(),
-            self.tcx.hir().span(ast_c.hir_id),
-            ObligationCauseCode::WellFormed(None),
-        );
-        c
+        self.register_wf_obligation(c.into(), span, ObligationCauseCode::WellFormed(None));
+        self.normalize_associated_types_in(span, c)
     }
 
     pub fn const_arg_to_const(

src/test/ui/closures/issue-52437.rs

@@ -2,5 +2,4 @@ fn main() {
     [(); &(&'static: loop { |x| {}; }) as *const _ as usize]
     //~^ ERROR: invalid label name `'static`
     //~| ERROR: type annotations needed
-    //~| ERROR mismatched types
 }

src/test/ui/closures/issue-52437.stderr

@@ -15,15 +15,6 @@ help: consider giving this closure parameter an explicit type
 LL |     [(); &(&'static: loop { |x: _| {}; }) as *const _ as usize]
    |                               +++
 
-error[E0308]: mismatched types
-  --> $DIR/issue-52437.rs:2:5
-   |
-LL | fn main() {
-   |           - expected `()` because of default return type
-LL |     [(); &(&'static: loop { |x| {}; }) as *const _ as usize]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found array `[(); _]`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0282, E0308.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/issues/issue-66706.rs

@@ -2,7 +2,6 @@ fn a() {
     [0; [|_: _ &_| ()].len()]
     //~^ ERROR expected `,`, found `&`
     //~| ERROR type annotations needed
-    //~| ERROR mismatched types
 }
 
 fn b() {
@@ -13,13 +12,11 @@ fn b() {
 fn c() {
     [0; [|&_: _ &_| {}; 0 ].len()]
     //~^ ERROR expected `,`, found `&`
-    //~| ERROR mismatched types
 }
 
 fn d() {
     [0; match [|f @ &ref _| () ] {} ]
     //~^ ERROR expected identifier, found reserved identifier `_`
-    //~| ERROR mismatched types
 }
 
 fn main() {}

src/test/ui/issues/issue-66706.stderr

@@ -7,21 +7,21 @@ LL |     [0; [|_: _ &_| ()].len()]
    |               help: missing `,`
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/issue-66706.rs:9:20
+  --> $DIR/issue-66706.rs:8:20
    |
 LL |     [0; [|f @ &ref _| {} ; 0 ].len() ];
    |                    ^ expected identifier, found reserved identifier
 
 error: expected `,`, found `&`
-  --> $DIR/issue-66706.rs:14:17
+  --> $DIR/issue-66706.rs:13:17
    |
 LL |     [0; [|&_: _ &_| {}; 0 ].len()]
    |                -^ expected `,`
    |                |
    |                help: missing `,`
 
 error: expected identifier, found reserved identifier `_`
-  --> $DIR/issue-66706.rs:20:26
+  --> $DIR/issue-66706.rs:18:26
    |
 LL |     [0; match [|f @ &ref _| () ] {} ]
    |                          ^ expected identifier, found reserved identifier
@@ -32,31 +32,6 @@ error[E0282]: type annotations needed
 LL |     [0; [|_: _ &_| ()].len()]
    |           ^ cannot infer type
 
-error[E0308]: mismatched types
-  --> $DIR/issue-66706.rs:2:5
-   |
-LL | fn a() {
-   |        - help: try adding a return type: `-> [i32; _]`
-LL |     [0; [|_: _ &_| ()].len()]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found array `[{integer}; _]`
-
-error[E0308]: mismatched types
-  --> $DIR/issue-66706.rs:14:5
-   |
-LL | fn c() {
-   |        - help: try adding a return type: `-> [i32; _]`
-LL |     [0; [|&_: _ &_| {}; 0 ].len()]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found array `[{integer}; _]`
-
-error[E0308]: mismatched types
-  --> $DIR/issue-66706.rs:20:5
-   |
-LL | fn d() {
-   |        - help: try adding a return type: `-> [i32; _]`
-LL |     [0; match [|f @ &ref _| () ] {} ]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found array `[{integer}; _]`
-
-error: aborting due to 8 previous errors
+error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0282, E0308.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0282`.