Rollup of 21 pull requests

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -466,7 +466,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     let spans = sess.psess.gated_spans.spans.borrow();
     macro_rules! gate_all {
         ($feature:ident, $explain:literal $(, $help:literal)?) => {
-            for &span in spans.get(&sym::$feature).into_iter().flatten() {
+            for &span in spans.get(&sym::$feature).into_flat_iter() {
                 gate!(visitor, $feature, span, $explain $(, $help)?);
             }
         };
@@ -527,13 +527,13 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     );
 
     // `associated_const_equality` will be stabilized as part of `min_generic_const_args`.
-    for &span in spans.get(&sym::associated_const_equality).into_iter().flatten() {
+    for &span in spans.get(&sym::associated_const_equality).into_flat_iter() {
         gate!(visitor, min_generic_const_args, span, "associated const equality is incomplete");
     }
 
     // `mgca_type_const_syntax` is part of `min_generic_const_args` so if
     // either or both are enabled we don't need to emit a feature error.
-    for &span in spans.get(&sym::mgca_type_const_syntax).into_iter().flatten() {
+    for &span in spans.get(&sym::mgca_type_const_syntax).into_flat_iter() {
         if visitor.features.min_generic_const_args()
             || visitor.features.mgca_type_const_syntax()
             || span.allows_unstable(sym::min_generic_const_args)
@@ -561,13 +561,13 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     //       it does **not** mean "`T` doesn't implement `Bound` (positively or negatively)"!
     //       The latter would be a SemVer hazard!
     if !sess.opts.unstable_opts.internal_testing_features || !visitor.features.negative_bounds() {
-        for &span in spans.get(&sym::negative_bounds).into_iter().flatten() {
+        for &span in spans.get(&sym::negative_bounds).into_flat_iter() {
             sess.dcx().emit_err(diagnostics::NegativeBoundUnsupported { span });
         }
     }
 
     if !visitor.features.never_patterns() {
-        for &span in spans.get(&sym::never_patterns).into_iter().flatten() {
+        for &span in spans.get(&sym::never_patterns).into_flat_iter() {
             if span.allows_unstable(sym::never_patterns) {
                 continue;
             }
@@ -585,7 +585,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     }
 
     // Yield exprs can be enabled either by `yield_expr`, by `coroutines` or by `gen_blocks`.
-    for &span in spans.get(&sym::yield_expr).into_iter().flatten() {
+    for &span in spans.get(&sym::yield_expr).into_flat_iter() {
         if (!visitor.features.coroutines() && !span.allows_unstable(sym::coroutines))
             && (!visitor.features.gen_blocks() && !span.allows_unstable(sym::gen_blocks))
             && (!visitor.features.yield_expr() && !span.allows_unstable(sym::yield_expr))
@@ -607,7 +607,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
 
     macro_rules! soft_gate_all_legacy_dont_use {
         ($feature:ident, $explain:literal) => {
-            for &span in spans.get(&sym::$feature).into_iter().flatten() {
+            for &span in spans.get(&sym::$feature).into_flat_iter() {
                 if !visitor.features.$feature() && !span.allows_unstable(sym::$feature) {
                     feature_warn(&visitor.sess, sym::$feature, span, $explain);
                 }
@@ -625,7 +625,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     soft_gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
     // tidy-alphabetical-end
 
-    for &span in spans.get(&sym::min_specialization).into_iter().flatten() {
+    for &span in spans.get(&sym::min_specialization).into_flat_iter() {
         if !visitor.features.specialization()
             && !visitor.features.min_specialization()
             && !span.allows_unstable(sym::specialization)

compiler/rustc_ast_passes/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(deref_patterns)]
 #![feature(iter_intersperse)]
 #![feature(iter_is_partitioned)]
+#![feature(option_into_flat_iter)]
 // tidy-alphabetical-end
 
 pub mod ast_validation;

compiler/rustc_attr_parsing/src/attributes/diagnostic/on_type_error.rs

@@ -18,6 +18,8 @@ pub(crate) struct OnTypeErrorParser {
 impl OnTypeErrorParser {
     fn parse<'sess>(&mut self, cx: &mut AcceptContext<'_, 'sess>, args: &ArgParser, mode: Mode) {
         if !cx.features().diagnostic_on_type_error() {
+            // `UnknownDiagnosticAttribute` is emitted in rustc_resolve/macros.rs
+            args.ignore_args();
             return;
         }
 

compiler/rustc_borrowck/src/dataflow.rs

@@ -476,9 +476,8 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
             .borrow_set
             .local_map
             .get(&place.local)
-            .into_iter()
-            .flat_map(|bs| bs.iter())
-            .copied();
+            .map(|bs| bs.iter().copied())
+            .into_flat_iter();
 
         // If the borrowed place is a local with no projections, all other borrows of this
         // local must conflict. This is purely an optimization so we don't have to call

compiler/rustc_borrowck/src/lib.rs

@@ -7,6 +7,7 @@
 #![feature(file_buffered)]
 #![feature(negative_impls)]
 #![feature(never_type)]
+#![feature(option_into_flat_iter)]
 #![feature(rustc_attrs)]
 #![feature(stmt_expr_attributes)]
 #![feature(try_blocks)]

compiler/rustc_borrowck/src/polonius/constraints.rs

@@ -152,7 +152,7 @@ impl LocalizedConstraintGraph {
                 // The physical edges present at this node are:
                 //
                 // 1. the typeck edges that flow from region to region *at this point*.
-                for &succ in self.edges.get(&node).into_iter().flatten() {
+                for &succ in self.edges.get(&node).into_flat_iter() {
                     let succ = LocalizedNode { region: succ, point: node.point };
                     successor_found(succ);
                 }
@@ -229,7 +229,7 @@ impl LocalizedConstraintGraph {
                 }
 
                 // And finally, we have the logical edges, materialized at this point.
-                for &logical_succ in self.logical_edges.get(&node.region).into_iter().flatten() {
+                for &logical_succ in self.logical_edges.get(&node.region).into_flat_iter() {
                     let succ = LocalizedNode { region: logical_succ, point: node.point };
                     successor_found(succ);
                 }

compiler/rustc_borrowck/src/region_infer/opaque_types/member_constraints.rs

@@ -49,7 +49,7 @@ pub(super) fn apply_member_constraints<'tcx>(
             rcx.scc_values.add_region(scc_a, scc_b);
         }
 
-        for defining_use in member_constraints.get(&scc_a).into_iter().flatten() {
+        for defining_use in member_constraints.get(&scc_a).into_flat_iter() {
             apply_member_constraint(rcx, scc_a, &defining_use.arg_regions);
         }
     }

compiler/rustc_borrowck/src/region_infer/values.rs

@@ -178,7 +178,7 @@ impl LivenessValues {
 
     /// Returns an iterator of all the points where `region` is live.
     fn live_points(&self, region: RegionVid) -> impl Iterator<Item = PointIndex> {
-        self.point_liveness(region).into_iter().flat_map(|set| set.iter())
+        self.point_liveness(region).map(|set| set.iter()).into_flat_iter()
     }
 
     /// For debugging purposes, returns a pretty-printed string of the points where the `region` is
@@ -348,13 +348,13 @@ impl<'tcx, N: Idx> RegionValues<'tcx, N> {
     pub(crate) fn locations_outlived_by(&self, r: N) -> impl Iterator<Item = Location> {
         self.points
             .row(r)
-            .into_iter()
-            .flat_map(move |set| set.iter().map(move |p| self.location_map.to_location(p)))
+            .map(move |set| set.iter().map(move |p| self.location_map.to_location(p)))
+            .into_flat_iter()
     }
 
     /// Returns just the universal regions that are contained in a given region's value.
     pub(crate) fn universal_regions_outlived_by(&self, r: N) -> impl Iterator<Item = RegionVid> {
-        self.free_regions.row(r).into_iter().flat_map(|set| set.iter())
+        self.free_regions.row(r).map(|set| set.iter()).into_flat_iter()
     }
 
     /// Returns all the elements contained in a given region's value.
@@ -364,8 +364,8 @@ impl<'tcx, N: Idx> RegionValues<'tcx, N> {
     ) -> impl Iterator<Item = ty::PlaceholderRegion<'tcx>> {
         self.placeholders
             .row(r)
-            .into_iter()
-            .flat_map(|set| set.iter())
+            .map(|set| set.iter())
+            .into_flat_iter()
             .map(move |p| self.placeholder_indices.lookup_placeholder(p))
     }
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -928,7 +928,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
         self.super_local_decl(local, local_decl);
 
         for user_ty in
-            local_decl.user_ty.as_deref().into_iter().flat_map(UserTypeProjections::projections)
+            local_decl.user_ty.as_deref().map(UserTypeProjections::projections).into_flat_iter()
         {
             let span = self.user_type_annotations[user_ty.base].span;
 

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -597,27 +597,7 @@ impl<'b, 'tcx> PredicateEmittingRelation<InferCtxt<'tcx>> for NllTypeRelating<'_
         );
     }
 
-    fn register_alias_relate_predicate(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) {
-        self.register_predicates([ty::Binder::dummy(match self.ambient_variance {
-            ty::Covariant => ty::PredicateKind::AliasRelate(
-                a.into(),
-                b.into(),
-                ty::AliasRelationDirection::Subtype,
-            ),
-            // a :> b is b <: a
-            ty::Contravariant => ty::PredicateKind::AliasRelate(
-                b.into(),
-                a.into(),
-                ty::AliasRelationDirection::Subtype,
-            ),
-            ty::Invariant => ty::PredicateKind::AliasRelate(
-                a.into(),
-                b.into(),
-                ty::AliasRelationDirection::Equate,
-            ),
-            ty::Bivariant => {
-                unreachable!("cannot defer an alias-relate goal with Bivariant variance (yet?)")
-            }
-        })]);
+    fn ambient_variance(&self) -> ty::Variance {
+        self.ambient_variance
     }
 }

compiler/rustc_codegen_ssa/src/assert_module_sources.rs

@@ -90,8 +90,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
     fn check_attrs(&mut self, attrs: &[hir::Attribute]) {
         for &(span, cgu_fields) in find_attr!(attrs,
             RustcCguTestAttr(e) => e)
-        .into_iter()
-        .flatten()
+        .into_flat_iter()
         {
             let (expected_reuse, comp_kind) = match cgu_fields {
                 CguFields::PartitionReused { .. } => (CguReuse::PreLto, ComparisonKind::AtLeast),

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1091,9 +1091,7 @@ fn link_natively(
             let get_objects = |objects: &CrtObjects, kind| {
                 objects
                     .get(&kind)
-                    .iter()
-                    .copied()
-                    .flatten()
+                    .into_flat_iter()
                     .map(|obj| {
                         get_object_file_path(sess, obj, self_contained_crt_objects).into_os_string()
                     })
@@ -2073,7 +2071,7 @@ fn add_pre_link_objects(
     } else {
         &empty
     };
-    for obj in objects.get(&link_output_kind).iter().copied().flatten() {
+    for obj in objects.get(&link_output_kind).into_flat_iter() {
         cmd.add_object(&get_object_file_path(sess, obj, self_contained));
     }
 }
@@ -2090,7 +2088,7 @@ fn add_post_link_objects(
     } else {
         &sess.target.post_link_objects
     };
-    for obj in objects.get(&link_output_kind).iter().copied().flatten() {
+    for obj in objects.get(&link_output_kind).into_flat_iter() {
         cmd.add_object(&get_object_file_path(sess, obj, self_contained));
     }
 }

compiler/rustc_codegen_ssa/src/lib.rs

@@ -2,6 +2,7 @@
 #![feature(deref_patterns)]
 #![feature(file_buffered)]
 #![feature(negative_impls)]
+#![feature(option_into_flat_iter)]
 #![feature(string_from_utf8_lossy_owned)]
 #![feature(trait_alias)]
 #![feature(try_blocks)]

compiler/rustc_codegen_ssa/src/mir/operand.rs

@@ -718,6 +718,34 @@ impl<'a, 'tcx, V: CodegenObject> OperandRefBuilder<'tcx, V> {
         OperandRefBuilder { val, layout }
     }
 
+    /// Creates an initialized builder for updating an existing `operand`.
+    ///
+    /// ICEs for [`BackendRepr::Memory`] types (other than ZSTs), which use
+    /// which use [`OperandValue::Ref`]. In this case, updates should be
+    /// performed by writing into the place
+    pub(super) fn from_existing(operand: OperandRef<'tcx, V>) -> Self {
+        let layout = operand.layout;
+        let val = match (operand.val, layout.backend_repr) {
+            (OperandValue::ZeroSized, _) => OperandValueBuilder::ZeroSized,
+            (OperandValue::Immediate(v), BackendRepr::Scalar(_)) => {
+                OperandValueBuilder::Immediate(Either::Left(v))
+            }
+            (OperandValue::Immediate(v), BackendRepr::SimdVector { .. }) => {
+                OperandValueBuilder::Vector(Either::Left(v))
+            }
+            (OperandValue::Pair(a, b), BackendRepr::ScalarPair(_, _)) => {
+                OperandValueBuilder::Pair(Either::Left(a), Either::Left(b))
+            }
+            (_, BackendRepr::Memory { .. }) => {
+                bug!("Cannot use non-ZST Memory-ABI type in operand builder: {layout:?}");
+            }
+            _ => {
+                bug!("Operand cannot be used with `from_existing`: {operand:?}")
+            }
+        };
+        OperandRefBuilder { val, layout }
+    }
+
     pub(super) fn insert_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
         &mut self,
         bx: &mut Bx,
@@ -829,6 +857,27 @@ impl<'a, 'tcx, V: CodegenObject> OperandRefBuilder<'tcx, V> {
         }
     }
 
+    /// Replaces the current immediate value at the offset `offset`
+    /// with the value `imm`. A value must already be present.
+    ///
+    /// This is used along with [`Self::from_existing`] to perform in-place updates
+    /// of any operand.
+    pub(super) fn update_imm(&mut self, offset: Size, imm: V) {
+        let is_zero_offset = offset == Size::ZERO;
+        match &mut self.val {
+            OperandValueBuilder::Immediate(val @ Either::Left(_)) if is_zero_offset => {
+                *val = Either::Left(imm);
+            }
+            OperandValueBuilder::Pair(fst @ Either::Left(_), _) if is_zero_offset => {
+                *fst = Either::Left(imm);
+            }
+            OperandValueBuilder::Pair(_, snd @ Either::Left(_)) if !is_zero_offset => {
+                *snd = Either::Left(imm);
+            }
+            _ => bug!("Tried to update {imm:?} at offset {offset:?} of {self:?}"),
+        }
+    }
+
     /// After having set all necessary fields, this converts the builder back
     /// to the normal `OperandRef`.
     ///