Rollup of 8 pull requests

compiler/rustc_feature/src/unstable.rs

@@ -578,7 +578,7 @@ declare_features! (
     /// be used to describe E or vise-versa.
     (unstable, result_ffi_guarantees, "1.80.0", Some(110503)),
     /// Allows bounding the return type of AFIT/RPITIT.
-    (incomplete, return_type_notation, "1.70.0", Some(109417)),
+    (unstable, return_type_notation, "1.70.0", Some(109417)),
     /// Allows `extern "rust-cold"`.
     (unstable, rust_cold_cc, "1.63.0", Some(97544)),
     /// Allows use of x86 SHA512, SM3 and SM4 target-features and intrinsics

compiler/rustc_hir/src/hir.rs

@@ -1668,10 +1668,17 @@ pub enum ArrayLen<'hir> {
 }
 
 impl ArrayLen<'_> {
-    pub fn hir_id(&self) -> HirId {
+    pub fn span(self) -> Span {
+        match self {
+            ArrayLen::Infer(arg) => arg.span,
+            ArrayLen::Body(body) => body.span(),
+        }
+    }
+
+    pub fn hir_id(self) -> HirId {
         match self {
-            ArrayLen::Infer(InferArg { hir_id, .. }) | ArrayLen::Body(ConstArg { hir_id, .. }) => {
-                *hir_id
+            ArrayLen::Infer(InferArg { hir_id, .. }) | ArrayLen::Body(&ConstArg { hir_id, .. }) => {
+                hir_id
             }
         }
     }

compiler/rustc_hir_typeck/src/expr.rs

@@ -1491,8 +1491,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expr: &'tcx hir::Expr<'tcx>,
     ) -> Ty<'tcx> {
         let tcx = self.tcx;
-        let count = self.lower_array_length(count);
-        if let Some(count) = count.try_eval_target_usize(tcx, self.param_env) {
+        let count_span = count.span();
+        let count = self.try_structurally_resolve_const(count_span, self.lower_array_length(count));
+
+        if let Some(count) = count.try_to_target_usize(tcx) {
             self.suggest_array_len(expr, count);
         }
 
@@ -1520,19 +1522,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return Ty::new_error(tcx, guar);
         }
 
-        self.check_repeat_element_needs_copy_bound(element, count, element_ty);
+        // If the length is 0, we don't create any elements, so we don't copy any.
+        // If the length is 1, we don't copy that one element, we move it. Only check
+        // for `Copy` if the length is larger, or unevaluated.
+        // FIXME(min_const_generic_exprs): We could perhaps defer this check so that
+        // we don't require `<?0t as Tr>::CONST` doesn't unnecessarily require `Copy`.
+        if count.try_to_target_usize(tcx).is_none_or(|x| x > 1) {
+            self.enforce_repeat_element_needs_copy_bound(element, element_ty);
+        }
 
         let ty = Ty::new_array_with_const_len(tcx, t, count);
-
         self.register_wf_obligation(ty.into(), expr.span, ObligationCauseCode::WellFormed(None));
-
         ty
     }
 
-    fn check_repeat_element_needs_copy_bound(
+    /// Requires that `element_ty` is `Copy` (unless it's a const expression itself).
+    fn enforce_repeat_element_needs_copy_bound(
         &self,
         element: &hir::Expr<'_>,
-        count: ty::Const<'tcx>,
         element_ty: Ty<'tcx>,
     ) {
         let tcx = self.tcx;
@@ -1565,27 +1572,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => traits::IsConstable::No,
         };
 
-        // If the length is 0, we don't create any elements, so we don't copy any. If the length is 1, we
-        // don't copy that one element, we move it. Only check for Copy if the length is larger.
-        if count.try_eval_target_usize(tcx, self.param_env).is_none_or(|len| len > 1) {
-            let lang_item = self.tcx.require_lang_item(LangItem::Copy, None);
-            let code = traits::ObligationCauseCode::RepeatElementCopy {
-                is_constable,
-                elt_type: element_ty,
-                elt_span: element.span,
-                elt_stmt_span: self
-                    .tcx
-                    .hir()
-                    .parent_iter(element.hir_id)
-                    .find_map(|(_, node)| match node {
-                        hir::Node::Item(it) => Some(it.span),
-                        hir::Node::Stmt(stmt) => Some(stmt.span),
-                        _ => None,
-                    })
-                    .expect("array repeat expressions must be inside an item or statement"),
-            };
-            self.require_type_meets(element_ty, element.span, code, lang_item);
-        }
+        let lang_item = self.tcx.require_lang_item(LangItem::Copy, None);
+        let code = traits::ObligationCauseCode::RepeatElementCopy {
+            is_constable,
+            elt_type: element_ty,
+            elt_span: element.span,
+            elt_stmt_span: self
+                .tcx
+                .hir()
+                .parent_iter(element.hir_id)
+                .find_map(|(_, node)| match node {
+                    hir::Node::Item(it) => Some(it.span),
+                    hir::Node::Stmt(stmt) => Some(stmt.span),
+                    _ => None,
+                })
+                .expect("array repeat expressions must be inside an item or statement"),
+        };
+        self.require_type_meets(element_ty, element.span, code, lang_item);
     }
 
     fn check_expr_tuple(
@@ -2800,9 +2803,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         len: ty::Const<'tcx>,
     ) {
         err.span_label(field.span, "unknown field");
-        if let (Some(len), Ok(user_index)) =
-            (len.try_eval_target_usize(self.tcx, self.param_env), field.as_str().parse::<u64>())
-        {
+        if let (Some(len), Ok(user_index)) = (
+            self.try_structurally_resolve_const(base.span, len).try_to_target_usize(self.tcx),
+            field.as_str().parse::<u64>(),
+        ) {
             let help = "instead of using tuple indexing, use array indexing";
             let applicability = if len < user_index {
                 Applicability::MachineApplicable

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1477,6 +1477,33 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self, sp), ret)]
+    pub fn try_structurally_resolve_const(&self, sp: Span, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
+        // FIXME(min_const_generic_exprs): We could process obligations here if `ct` is a var.
+
+        if self.next_trait_solver()
+            && let ty::ConstKind::Unevaluated(..) = ct.kind()
+        {
+            // We need to use a separate variable here as otherwise the temporary for
+            // `self.fulfillment_cx.borrow_mut()` is alive in the `Err` branch, resulting
+            // in a reentrant borrow, causing an ICE.
+            let result = self
+                .at(&self.misc(sp), self.param_env)
+                .structurally_normalize_const(ct, &mut **self.fulfillment_cx.borrow_mut());
+            match result {
+                Ok(normalized_ct) => normalized_ct,
+                Err(errors) => {
+                    let guar = self.err_ctxt().report_fulfillment_errors(errors);
+                    return ty::Const::new_error(self.tcx, guar);
+                }
+            }
+        } else if self.tcx.features().generic_const_exprs {
+            ct.normalize(self.tcx, self.param_env)
+        } else {
+            ct
+        }
+    }
+
     /// Resolves `ty` by a single level if `ty` is a type variable.
     ///
     /// When the new solver is enabled, this will also attempt to normalize

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1502,7 +1502,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Create an dummy type `&[_]` so that both &[] and `&Vec<T>` can coerce to it.
         let dummy_ty = if let ty::Array(elem_ty, size) = peeled.kind()
             && let ty::Infer(_) = elem_ty.kind()
-            && size.try_eval_target_usize(self.tcx, self.param_env) == Some(0)
+            && self
+                .try_structurally_resolve_const(provided_expr.span, *size)
+                .try_to_target_usize(self.tcx)
+                == Some(0)
         {
             let slice = Ty::new_slice(self.tcx, *elem_ty);
             Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_static, slice)

compiler/rustc_hir_typeck/src/intrinsicck.rs

@@ -101,7 +101,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             Ok(SizeSkeleton::Generic(size)) => {
-                if let Some(size) = size.try_eval_target_usize(tcx, self.param_env) {
+                if let Some(size) =
+                    self.try_structurally_resolve_const(span, size).try_to_target_usize(tcx)
+                {
                     format!("{size} bytes")
                 } else {
                     format!("generic size {size}")

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1721,20 +1721,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
         }
 
-        if item_name.name == sym::as_str && rcvr_ty.peel_refs().is_str() {
-            let msg = "remove this method call";
-            let mut fallback_span = true;
-            if let SelfSource::MethodCall(expr) = source {
-                let call_expr = self.tcx.hir().expect_expr(self.tcx.parent_hir_id(expr.hir_id));
-                if let Some(span) = call_expr.span.trim_start(expr.span) {
-                    err.span_suggestion(span, msg, "", Applicability::MachineApplicable);
-                    fallback_span = false;
-                }
-            }
-            if fallback_span {
-                err.span_label(span, msg);
-            }
-        } else if let Some(similar_candidate) = similar_candidate {
+        if let Some(similar_candidate) = similar_candidate {
             // Don't emit a suggestion if we found an actual method
             // that had unsatisfied trait bounds
             if unsatisfied_predicates.is_empty()

compiler/rustc_hir_typeck/src/pat.rs

@@ -2412,7 +2412,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         len: ty::Const<'tcx>,
         min_len: u64,
     ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
-        let len = len.try_eval_target_usize(self.tcx, self.param_env);
+        let len = self.try_structurally_resolve_const(span, len).try_to_target_usize(self.tcx);
 
         let guar = if let Some(len) = len {
             // Now we know the length...

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -57,7 +57,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 this.in_scope(region_scope, lint_level, |this| this.as_rvalue(block, scope, value))
             }
             ExprKind::Repeat { value, count } => {
-                if Some(0) == count.try_eval_target_usize(this.tcx, this.param_env) {
+                if Some(0) == count.try_to_target_usize(this.tcx) {
                     this.build_zero_repeat(block, value, scope, source_info)
                 } else {
                     let value_operand = unpack!(

compiler/rustc_mir_build/src/build/matches/match_pair.rs

@@ -42,7 +42,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let tcx = self.tcx;
         let (min_length, exact_size) = if let Some(place_resolved) = place.try_to_place(self) {
             match place_resolved.ty(&self.local_decls, tcx).ty.kind() {
-                ty::Array(_, length) => (length.eval_target_usize(tcx, self.param_env), true),
+                ty::Array(_, length) => (
+                    length
+                        .try_to_target_usize(tcx)
+                        .expect("expected len of array pat to be definite"),
+                    true,
+                ),
                 _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
             }
         } else {

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

@@ -441,7 +441,9 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             ty::Slice(..) => PatKind::Slice { prefix, slice, suffix },
             // Fixed-length array, `[T; len]`.
             ty::Array(_, len) => {
-                let len = len.eval_target_usize(self.tcx, self.param_env);
+                let len = len
+                    .try_to_target_usize(self.tcx)
+                    .expect("expected len of array pat to be definite");
                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
                 PatKind::Array { prefix, slice, suffix }
             }

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -352,7 +352,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             ty::Array(sub_ty, len) => {
                 // We treat arrays of a constant but unknown length like slices.
                 ConstructorSet::Slice {
-                    array_len: len.try_eval_target_usize(cx.tcx, cx.param_env).map(|l| l as usize),
+                    array_len: len.try_to_target_usize(cx.tcx).map(|l| l as usize),
                     subtype_is_empty: cx.is_uninhabited(*sub_ty),
                 }
             }
@@ -685,9 +685,12 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             }
             PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
                 let array_len = match ty.kind() {
-                    ty::Array(_, length) => {
-                        Some(length.eval_target_usize(cx.tcx, cx.param_env) as usize)
-                    }
+                    ty::Array(_, length) => Some(
+                        length
+                            .try_to_target_usize(cx.tcx)
+                            .expect("expected len of array pat to be definite")
+                            as usize,
+                    ),
                     ty::Slice(_) => None,
                     _ => span_bug!(pat.span, "bad ty {} for slice pattern", ty.inner()),
                 };

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -17,7 +17,7 @@ use rustc_middle::traits::select::OverflowError;
 use rustc_middle::traits::SignatureMismatchData;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
-use rustc_middle::ty::fold::{BottomUpFolder, TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::print::{
     with_forced_trimmed_paths, FmtPrinter, Print, PrintTraitPredicateExt as _,
     PrintTraitRefExt as _,
@@ -1794,22 +1794,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         return false;
                     }
 
-                    let cand = self.resolve_vars_if_possible(impl_trait_ref).fold_with(
-                        &mut BottomUpFolder {
-                            tcx: self.tcx,
-                            ty_op: |ty| ty,
-                            lt_op: |lt| lt,
-                            ct_op: |ct| ct.normalize(self.tcx, ty::ParamEnv::empty()),
-                        },
-                    );
-                    if cand.references_error() {
+                    let impl_trait_ref = self.resolve_vars_if_possible(impl_trait_ref);
+                    if impl_trait_ref.references_error() {
                         return false;
                     }
                     err.highlighted_help(vec![
-                        StringPart::normal(format!("the trait `{}` ", cand.print_trait_sugared())),
+                        StringPart::normal(format!(
+                            "the trait `{}` ",
+                            impl_trait_ref.print_trait_sugared()
+                        )),
                         StringPart::highlighted("is"),
                         StringPart::normal(" implemented for `"),
-                        StringPart::highlighted(cand.self_ty().to_string()),
+                        StringPart::highlighted(impl_trait_ref.self_ty().to_string()),
                         StringPart::normal("`"),
                     ]);
 
@@ -1921,15 +1917,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let mut impl_candidates: Vec<_> = impl_candidates
             .iter()
             .cloned()
+            .filter(|cand| !cand.trait_ref.references_error())
             .map(|mut cand| {
-                // Fold the consts so that they shows up as, e.g., `10`
-                // instead of `core::::array::{impl#30}::{constant#0}`.
-                cand.trait_ref = cand.trait_ref.fold_with(&mut BottomUpFolder {
-                    tcx: self.tcx,
-                    ty_op: |ty| ty,
-                    lt_op: |lt| lt,
-                    ct_op: |ct| ct.normalize(self.tcx, ty::ParamEnv::empty()),
-                });
+                // Normalize the trait ref in its *own* param-env so
+                // that consts are folded and any trivial projections
+                // are normalized.
+                cand.trait_ref = self
+                    .tcx
+                    .try_normalize_erasing_regions(
+                        self.tcx.param_env(cand.impl_def_id),
+                        cand.trait_ref,
+                    )
+                    .unwrap_or(cand.trait_ref);
                 cand
             })
             .collect();

compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

@@ -4621,7 +4621,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     format!("&{}{ty}", mutability.prefix_str())
                 }
             }
-            ty::Array(ty, len) if let Some(len) = len.try_eval_target_usize(tcx, param_env) => {
+            ty::Array(ty, len) if let Some(len) = len.try_to_target_usize(tcx) => {
                 if len == 0 {
                     "[]".to_string()
                 } else if self.type_is_copy_modulo_regions(param_env, ty) || len == 1 {

compiler/rustc_trait_selection/src/traits/structural_normalize.rs

@@ -46,4 +46,44 @@ impl<'tcx> At<'_, 'tcx> {
             Ok(self.normalize(ty).into_value_registering_obligations(self.infcx, fulfill_cx))
         }
     }
+
+    fn structurally_normalize_const<E: 'tcx>(
+        &self,
+        ct: ty::Const<'tcx>,
+        fulfill_cx: &mut dyn TraitEngine<'tcx, E>,
+    ) -> Result<ty::Const<'tcx>, Vec<E>> {
+        assert!(!ct.is_ct_infer(), "should have resolved vars before calling");
+
+        if self.infcx.next_trait_solver() {
+            let ty::ConstKind::Unevaluated(..) = ct.kind() else {
+                return Ok(ct);
+            };
+
+            let new_infer_ct = self.infcx.next_const_var(self.cause.span);
+
+            // We simply emit an `alias-eq` goal here, since that will take care of
+            // normalizing the LHS of the projection until it is a rigid projection
+            // (or a not-yet-defined opaque in scope).
+            let obligation = Obligation::new(
+                self.infcx.tcx,
+                self.cause.clone(),
+                self.param_env,
+                ty::PredicateKind::AliasRelate(
+                    ct.into(),
+                    new_infer_ct.into(),
+                    ty::AliasRelationDirection::Equate,
+                ),
+            );
+
+            fulfill_cx.register_predicate_obligation(self.infcx, obligation);
+            let errors = fulfill_cx.select_where_possible(self.infcx);
+            if !errors.is_empty() {
+                return Err(errors);
+            }
+
+            Ok(self.infcx.resolve_vars_if_possible(new_infer_ct))
+        } else {
+            Ok(self.normalize(ct).into_value_registering_obligations(self.infcx, fulfill_cx))
+        }
+    }
 }