Rollup of 7 pull requests

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1101,9 +1101,18 @@ fn should_encode_const(def_kind: DefKind) -> bool {
     }
 }
 
-// Return `false` to avoid encoding impl trait in trait, while we don't use the query.
-fn should_encode_fn_impl_trait_in_trait<'tcx>(_tcx: TyCtxt<'tcx>, _def_id: DefId) -> bool {
-    false
+// We only encode impl trait in trait when using `lower-impl-trait-in-trait-to-assoc-ty` unstable
+// option.
+fn should_encode_fn_impl_trait_in_trait<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
+    if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty
+        && let Some(assoc_item) = tcx.opt_associated_item(def_id)
+        && assoc_item.container == ty::AssocItemContainer::TraitContainer
+        && assoc_item.kind == ty::AssocKind::Fn
+    {
+        true
+    } else {
+        false
+    }
 }
 
 impl<'a, 'tcx> EncodeContext<'a, 'tcx> {

compiler/rustc_middle/src/hir/mod.rs

@@ -177,6 +177,7 @@ pub fn provide(providers: &mut Providers) {
         }
     };
     providers.opt_def_kind = |tcx, def_id| tcx.hir().opt_def_kind(def_id.expect_local());
+    providers.opt_rpitit_info = |_, _| None;
     providers.all_local_trait_impls = |tcx, ()| &tcx.resolutions(()).trait_impls;
     providers.expn_that_defined = |tcx, id| {
         let id = id.expect_local();

compiler/rustc_middle/src/query/mod.rs

@@ -90,6 +90,7 @@ rustc_queries! {
     /// Definitions that were generated with no HIR, would be feeded to return `None`.
     query opt_local_def_id_to_hir_id(key: LocalDefId) -> Option<hir::HirId>{
         desc { |tcx| "getting HIR ID of `{}`", tcx.def_path_str(key.to_def_id()) }
+        feedable
     }
 
     /// Gives access to the HIR node's parent for the HIR owner `key`.
@@ -166,6 +167,7 @@ rustc_queries! {
         }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     query collect_return_position_impl_trait_in_trait_tys(key: DefId)
@@ -222,6 +224,7 @@ rustc_queries! {
         arena_cache
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     /// Maps from the `DefId` of an item (trait/struct/enum/fn) to the
@@ -264,6 +267,7 @@ rustc_queries! {
         desc { |tcx| "finding item bounds for `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     /// Elaborated version of the predicates from `explicit_item_bounds`.
@@ -588,6 +592,7 @@ rustc_queries! {
         desc { |tcx| "computing explicit predicates of `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     /// Returns the inferred outlives predicates (e.g., for `struct
@@ -596,6 +601,7 @@ rustc_queries! {
         desc { |tcx| "computing inferred outlives predicates of `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     /// Maps from the `DefId` of a trait to the list of
@@ -728,6 +734,7 @@ rustc_queries! {
         desc { |tcx| "computing associated item data for `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
+        feedable
     }
 
     /// Collects the associated items defined on a trait or impl.
@@ -1142,6 +1149,15 @@ rustc_queries! {
         desc { |tcx| "looking up definition kind of `{}`", tcx.def_path_str(def_id) }
         cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
+        feedable
+    }
+
+    /// The `opt_rpitit_info` query returns the pair of the def id of the function where the RPIT
+    /// is defined and the opaque def id if any.
+    query opt_rpitit_info(def_id: DefId) -> Option<ty::ImplTraitInTraitData> {
+        desc { |tcx| "opt_rpitit_info `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
+        feedable
     }
 
     /// Gets the span for the definition.
@@ -1157,6 +1173,7 @@ rustc_queries! {
         desc { |tcx| "looking up span for `{}`'s identifier", tcx.def_path_str(def_id) }
         cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
+        feedable
     }
 
     query lookup_stability(def_id: DefId) -> Option<attr::Stability> {
@@ -1498,6 +1515,7 @@ rustc_queries! {
         desc { |tcx| "looking up whether `{}` is a default impl", tcx.def_path_str(def_id) }
         cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
+        feedable
     }
 
     query check_well_formed(key: hir::OwnerId) -> () {
@@ -1695,6 +1713,7 @@ rustc_queries! {
     query visibility(def_id: DefId) -> ty::Visibility<DefId> {
         desc { |tcx| "computing visibility of `{}`", tcx.def_path_str(def_id) }
         separate_provide_extern
+        feedable
     }
 
     query inhabited_predicate_adt(key: DefId) -> ty::inhabitedness::InhabitedPredicate<'tcx> {

compiler/rustc_middle/src/ty/mod.rs

@@ -2071,6 +2071,12 @@ pub enum ImplOverlapKind {
     Issue33140,
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
+pub enum ImplTraitInTraitData {
+    Trait { fn_def_id: DefId, opaque_def_id: DefId },
+    Impl { fn_def_id: DefId },
+}
+
 impl<'tcx> TyCtxt<'tcx> {
     pub fn typeck_body(self, body: hir::BodyId) -> &'tcx TypeckResults<'tcx> {
         self.typeck(self.hir().body_owner_def_id(body))

compiler/rustc_parse/locales/en-US.ftl

@@ -151,6 +151,10 @@ parse_missing_in_in_for_loop = missing `in` in `for` loop
 parse_missing_expression_in_for_loop = missing expression to iterate on in `for` loop
     .suggestion = try adding an expression to the `for` loop
 
+parse_loop_else = `{$loop_kind}...else` loops are not supported
+    .note = consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
+    .loop_keyword = `else` is attached to this loop
+
 parse_missing_comma_after_match_arm = expected `,` following `match` arm
     .suggestion = missing a comma here to end this `match` arm
 

compiler/rustc_parse/src/errors.rs

@@ -451,6 +451,17 @@ pub(crate) struct MissingExpressionInForLoop {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_loop_else)]
+#[note]
+pub(crate) struct LoopElseNotSupported {
+    #[primary_span]
+    pub span: Span,
+    pub loop_kind: &'static str,
+    #[label(parse_loop_keyword)]
+    pub loop_kw: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_missing_comma_after_match_arm)]
 pub(crate) struct MissingCommaAfterMatchArm {

compiler/rustc_parse/src/parser/expr.rs

@@ -2503,9 +2503,27 @@ impl<'a> Parser<'a> {
         let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
 
         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
+
+        self.recover_loop_else("for", lo)?;
+
         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
     }
 
+    /// Recovers from an `else` clause after a loop (`for...else`, `while...else`)
+    fn recover_loop_else(&mut self, loop_kind: &'static str, loop_kw: Span) -> PResult<'a, ()> {
+        if self.token.is_keyword(kw::Else) && self.may_recover() {
+            let else_span = self.token.span;
+            self.bump();
+            let else_clause = self.parse_expr_else()?;
+            self.sess.emit_err(errors::LoopElseNotSupported {
+                span: else_span.to(else_clause.span),
+                loop_kind,
+                loop_kw,
+            });
+        }
+        Ok(())
+    }
+
     fn error_missing_in_for_loop(&mut self) {
         let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
             // Possibly using JS syntax (#75311).
@@ -2530,6 +2548,9 @@ impl<'a> Parser<'a> {
             err.span_label(cond.span, "this `while` condition successfully parsed");
             err
         })?;
+
+        self.recover_loop_else("while", lo)?;
+
         Ok(self.mk_expr_with_attrs(
             lo.to(self.prev_token.span),
             ExprKind::While(cond, body, opt_label),
@@ -2541,6 +2562,7 @@ impl<'a> Parser<'a> {
     fn parse_expr_loop(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
         let loop_span = self.prev_token.span;
         let (attrs, body) = self.parse_inner_attrs_and_block()?;
+        self.recover_loop_else("loop", lo)?;
         Ok(self.mk_expr_with_attrs(
             lo.to(self.prev_token.span),
             ExprKind::Loop(body, opt_label, loop_span),

compiler/rustc_session/src/options.rs

@@ -1503,6 +1503,9 @@ options! {
         "what location details should be tracked when using caller_location, either \
         `none`, or a comma separated list of location details, for which \
         valid options are `file`, `line`, and `column` (default: `file,line,column`)"),
+    lower_impl_trait_in_trait_to_assoc_ty: bool = (false, parse_bool, [TRACKED],
+        "modify the lowering strategy for `impl Trait` in traits so that they are lowered to \
+        generic associated types"),
     ls: bool = (false, parse_bool, [UNTRACKED],
         "list the symbols defined by a library crate (default: no)"),
     macro_backtrace: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_ty_utils/src/assoc.rs

@@ -4,7 +4,8 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::intravisit::{self, Visitor};
-use rustc_middle::ty::{self, DefIdTree, TyCtxt};
+use rustc_middle::ty::{self, DefIdTree, ImplTraitInTraitData, InternalSubsts, TyCtxt};
+use rustc_span::symbol::kw;
 
 pub fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers {
@@ -21,9 +22,37 @@ pub fn provide(providers: &mut ty::query::Providers) {
 fn associated_item_def_ids(tcx: TyCtxt<'_>, def_id: DefId) -> &[DefId] {
     let item = tcx.hir().expect_item(def_id.expect_local());
     match item.kind {
-        hir::ItemKind::Trait(.., ref trait_item_refs) => tcx.arena.alloc_from_iter(
-            trait_item_refs.iter().map(|trait_item_ref| trait_item_ref.id.owner_id.to_def_id()),
-        ),
+        hir::ItemKind::Trait(.., ref trait_item_refs) => {
+            if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty {
+                // We collect RPITITs for each trait method's return type and create a
+                // corresponding associated item using associated_items_for_impl_trait_in_trait
+                // query.
+                tcx.arena.alloc_from_iter(
+                    trait_item_refs
+                        .iter()
+                        .map(|trait_item_ref| trait_item_ref.id.owner_id.to_def_id())
+                        .chain(
+                            trait_item_refs
+                                .iter()
+                                .filter(|trait_item_ref| {
+                                    matches!(trait_item_ref.kind, hir::AssocItemKind::Fn { .. })
+                                })
+                                .flat_map(|trait_item_ref| {
+                                    let trait_fn_def_id =
+                                        trait_item_ref.id.owner_id.def_id.to_def_id();
+                                    tcx.associated_items_for_impl_trait_in_trait(trait_fn_def_id)
+                                })
+                                .map(|def_id| *def_id),
+                        ),
+                )
+            } else {
+                tcx.arena.alloc_from_iter(
+                    trait_item_refs
+                        .iter()
+                        .map(|trait_item_ref| trait_item_ref.id.owner_id.to_def_id()),
+                )
+            }
+        }
         hir::ItemKind::Impl(ref impl_) => tcx.arena.alloc_from_iter(
             impl_.items.iter().map(|impl_item_ref| impl_item_ref.id.owner_id.to_def_id()),
         ),
@@ -193,10 +222,65 @@ fn associated_item_for_impl_trait_in_trait(
     let span = tcx.def_span(opaque_ty_def_id);
     let trait_assoc_ty =
         tcx.at(span).create_def(trait_def_id.expect_local(), DefPathData::ImplTraitAssocTy);
-    trait_assoc_ty.def_id()
+
+    let local_def_id = trait_assoc_ty.def_id();
+    let def_id = local_def_id.to_def_id();
+
+    trait_assoc_ty.opt_def_kind(Some(DefKind::AssocTy));
+
+    // There's no HIR associated with this new synthesized `def_id`, so feed
+    // `opt_local_def_id_to_hir_id` with `None`.
+    trait_assoc_ty.opt_local_def_id_to_hir_id(None);
+
+    // Copy span of the opaque.
+    trait_assoc_ty.def_ident_span(Some(span));
+
+    // Add the def_id of the function and opaque that generated this synthesized associated type.
+    trait_assoc_ty.opt_rpitit_info(Some(ImplTraitInTraitData::Trait {
+        fn_def_id,
+        opaque_def_id: opaque_ty_def_id.to_def_id(),
+    }));
+
+    trait_assoc_ty.associated_item(ty::AssocItem {
+        name: kw::Empty,
+        kind: ty::AssocKind::Type,
+        def_id,
+        trait_item_def_id: None,
+        container: ty::TraitContainer,
+        fn_has_self_parameter: false,
+    });
+
+    // Copy visility of the containing function.
+    trait_assoc_ty.visibility(tcx.visibility(fn_def_id));
+
+    // Copy impl_defaultness of the containing function.
+    trait_assoc_ty.impl_defaultness(tcx.impl_defaultness(fn_def_id));
+
+    // Copy type_of of the opaque.
+    trait_assoc_ty.type_of(ty::EarlyBinder(tcx.mk_opaque(
+        opaque_ty_def_id.to_def_id(),
+        InternalSubsts::identity_for_item(tcx, opaque_ty_def_id.to_def_id()),
+    )));
+
+    // Copy generics_of of the opaque.
+    trait_assoc_ty.generics_of(tcx.generics_of(opaque_ty_def_id).clone());
+
+    // There are no predicates for the synthesized associated type.
+    trait_assoc_ty.explicit_predicates_of(ty::GenericPredicates {
+        parent: Some(trait_def_id),
+        predicates: &[],
+    });
+
+    // There are no inferred outlives for the synthesized associated type.
+    trait_assoc_ty.inferred_outlives_of(&[]);
+
+    // FIXME implement this.
+    trait_assoc_ty.explicit_item_bounds(&[]);
+
+    local_def_id
 }
 
-/// Given an `trait_assoc_def_id` that corresponds to a previously synthethized impl trait in trait
+/// Given an `trait_assoc_def_id` that corresponds to a previously synthesized impl trait in trait
 /// into an associated type and an `impl_def_id` corresponding to an impl block, create and return
 /// the corresponding associated item inside the impl block.
 fn impl_associated_item_for_impl_trait_in_trait(

library/alloc/src/collections/vec_deque/mod.rs

@@ -1924,7 +1924,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     #[stable(feature = "append", since = "1.4.0")]
     pub fn append(&mut self, other: &mut Self) {
         if T::IS_ZST {
-            self.len += other.len;
+            self.len = self.len.checked_add(other.len).expect("capacity overflow");
             other.len = 0;
             other.head = 0;
             return;

library/alloc/tests/vec_deque.rs

@@ -1045,6 +1045,20 @@ fn test_append_double_drop() {
     assert_eq!(count_b, 1);
 }
 
+#[test]
+#[should_panic]
+fn test_append_zst_capacity_overflow() {
+    let mut v = Vec::with_capacity(usize::MAX);
+    // note: using resize instead of set_len here would
+    //       be *extremely* slow in unoptimized builds.
+    // SAFETY: `v` has capacity `usize::MAX`, and no initialization
+    //         is needed for empty tuples.
+    unsafe { v.set_len(usize::MAX) };
+    let mut v = VecDeque::from(v);
+    let mut w = vec![()].into();
+    v.append(&mut w);
+}
+
 #[test]
 fn test_retain() {
     let mut buf = VecDeque::new();