Auto merge of rust-lang#91221 - matthiaskrgr:rollup-iuz3gxq, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#89359 (Various fixes for const_trait_impl)
 - rust-lang#90499 (Link with default MACOSX_DEPLOYMENT_TARGET if not otherwise specified.)
 - rust-lang#91096 (Print associated types on opaque `impl Trait` types)
 - rust-lang#91111 (Do not visit attributes in `ItemLowerer`.)
 - rust-lang#91162 (explain why CTFE/Miri perform truncation on shift offset)
 - rust-lang#91185 (Remove `-Z force-overflow-checks`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_ast_lowering/src/item.rs

@@ -40,6 +40,11 @@ impl ItemLowerer<'_, '_, '_> {
 }
 
 impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
+    fn visit_attribute(&mut self, _: &'a Attribute) {
+        // We do not want to lower expressions that appear in attributes,
+        // as they are not accessible to the rest of the HIR.
+    }
+
     fn visit_item(&mut self, item: &'a Item) {
         let hir_id = self.lctx.with_hir_id_owner(item.id, |lctx| {
             let node = lctx.without_in_scope_lifetime_defs(|lctx| lctx.lower_item(item));

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -130,7 +130,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             let signed = left_layout.abi.is_signed();
             let size = u128::from(left_layout.size.bits());
             let overflow = r >= size;
-            let r = r % size; // mask to type size
+            // The shift offset is implicitly masked to the type size, to make sure this operation
+            // is always defined. This is the one MIR operator that does *not* directly map to a
+            // single LLVM operation. See
+            // <https://github.com/rust-lang/rust/blob/a3b9405ae7bb6ab4e8103b414e75c44598a10fd2/compiler/rustc_codegen_ssa/src/common.rs#L131-L158>
+            // for the corresponding truncation in our codegen backends.
+            let r = r % size;
             let r = u32::try_from(r).unwrap(); // we masked so this will always fit
             let result = if signed {
                 let l = self.sign_extend(l, left_layout) as i128;

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -1004,11 +1004,12 @@ impl Visitor<'tcx> for Checker<'mir, 'tcx> {
                 }
 
                 let mut err_span = self.span;
+                let ty_of_dropped_place = dropped_place.ty(self.body, self.tcx).ty;
 
-                let ty_needs_non_const_drop = qualifs::NeedsNonConstDrop::in_any_value_of_ty(
-                    self.ccx,
-                    dropped_place.ty(self.body, self.tcx).ty,
-                );
+                let ty_needs_non_const_drop =
+                    qualifs::NeedsNonConstDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place);
+
+                debug!(?ty_of_dropped_place, ?ty_needs_non_const_drop);
 
                 if !ty_needs_non_const_drop {
                     return;

compiler/rustc_hir/src/lang_items.rs

@@ -268,6 +268,7 @@ language_item_table! {
     Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
     GeneratorState,          sym::generator_state,     gen_state,                  Target::Enum,           GenericRequirement::None;
     Generator,               sym::generator,           gen_trait,                  Target::Trait,          GenericRequirement::Minimum(1);
+    GeneratorReturn,         sym::generator_return,    generator_return,           Target::AssocTy,        GenericRequirement::None;
     Unpin,                   sym::unpin,               unpin_trait,                Target::Trait,          GenericRequirement::None;
     Pin,                     sym::pin,                 pin_type,                   Target::Struct,         GenericRequirement::None;
 

compiler/rustc_interface/src/tests.rs

@@ -726,7 +726,6 @@ fn test_debugging_options_tracking_hash() {
     tracked!(dep_info_omit_d_target, true);
     tracked!(dual_proc_macros, true);
     tracked!(fewer_names, Some(true));
-    tracked!(force_overflow_checks, Some(true));
     tracked!(force_unstable_if_unmarked, true);
     tracked!(fuel, Some(("abc".to_string(), 99)));
     tracked!(function_sections, Some(false));

compiler/rustc_middle/src/mir/mod.rs

@@ -2246,8 +2246,12 @@ pub enum BinOp {
     /// The `*` operator (multiplication)
     Mul,
     /// The `/` operator (division)
+    ///
+    /// Division by zero is UB.
     Div,
     /// The `%` operator (modulus)
+    ///
+    /// Using zero as the modulus (second operand) is UB.
     Rem,
     /// The `^` operator (bitwise xor)
     BitXor,
@@ -2256,8 +2260,12 @@ pub enum BinOp {
     /// The `|` operator (bitwise or)
     BitOr,
     /// The `<<` operator (shift left)
+    ///
+    /// The offset is truncated to the size of the first operand before shifting.
     Shl,
     /// The `>>` operator (shift right)
+    ///
+    /// The offset is truncated to the size of the first operand before shifting.
     Shr,
     /// The `==` operator (equality)
     Eq,

compiler/rustc_middle/src/traits/mod.rs

@@ -7,6 +7,7 @@ pub mod query;
 pub mod select;
 pub mod specialization_graph;
 mod structural_impls;
+pub mod util;
 
 use crate::infer::canonical::Canonical;
 use crate::thir::abstract_const::NotConstEvaluatable;

compiler/rustc_middle/src/traits/util.rs

@@ -0,0 +1,49 @@
+use rustc_data_structures::stable_set::FxHashSet;
+
+use crate::ty::{PolyTraitRef, TyCtxt};
+
+/// Given a PolyTraitRef, get the PolyTraitRefs of the trait's (transitive) supertraits.
+///
+/// A simplfied version of the same function at `rustc_infer::traits::util::supertraits`.
+pub fn supertraits<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    trait_ref: PolyTraitRef<'tcx>,
+) -> impl Iterator<Item = PolyTraitRef<'tcx>> {
+    Elaborator { tcx, visited: FxHashSet::from_iter([trait_ref]), stack: vec![trait_ref] }
+}
+
+struct Elaborator<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    visited: FxHashSet<PolyTraitRef<'tcx>>,
+    stack: Vec<PolyTraitRef<'tcx>>,
+}
+
+impl<'tcx> Elaborator<'tcx> {
+    fn elaborate(&mut self, trait_ref: PolyTraitRef<'tcx>) {
+        let supertrait_refs = self
+            .tcx
+            .super_predicates_of(trait_ref.def_id())
+            .predicates
+            .into_iter()
+            .flat_map(|(pred, _)| {
+                pred.subst_supertrait(self.tcx, &trait_ref).to_opt_poly_trait_ref()
+            })
+            .map(|t| t.value)
+            .filter(|supertrait_ref| self.visited.insert(*supertrait_ref));
+
+        self.stack.extend(supertrait_refs);
+    }
+}
+
+impl<'tcx> Iterator for Elaborator<'tcx> {
+    type Item = PolyTraitRef<'tcx>;
+
+    fn next(&mut self) -> Option<PolyTraitRef<'tcx>> {
+        if let Some(trait_ref) = self.stack.pop() {
+            self.elaborate(trait_ref);
+            Some(trait_ref)
+        } else {
+            None
+        }
+    }
+}