Auto merge of #142685 - Kobzol:rollup-8f3g8yf, r=Kobzol

Rollup of 11 pull requests

Successful merges:

 - rust-lang/rust#140774 (Affirm `-Cforce-frame-pointers=off` does not override)
 - rust-lang/rust#141610 (Stabilize `feature(generic_arg_infer)`)
 - rust-lang/rust#142383 (CodeGen: rework Aggregate implemention for rvalue_creates_operand cases)
 - rust-lang/rust#142591 (Add spawn APIs for BootstrapCommand to support deferred command execution)
 - rust-lang/rust#142619 (apply clippy::or_fun_call)
 - rust-lang/rust#142624 (Actually take `--build` into account in bootstrap)
 - rust-lang/rust#142627 (Add `StepMetadata` to describe steps)
 - rust-lang/rust#142660 (remove joboet from review rotation)
 - rust-lang/rust#142666 (Skip tidy triagebot linkcheck if `triagebot.toml` doesn't exist)
 - rust-lang/rust#142672 (Clarify bootstrap tools description)
 - rust-lang/rust#142674 (remove duplicate crash test)

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

21 files changed, 167 insertions, 148 deletions

diff --git a/compiler/rustc_ast_lowering/messages.ftl b/compiler/rustc_ast_lowering/messages.ftl
index 50eb7c7ae99..c6472fd45fa 100644
--- a/compiler/rustc_ast_lowering/messages.ftl
+++ b/compiler/rustc_ast_lowering/messages.ftl
@@ -172,9 +172,6 @@ ast_lowering_template_modifier = template modifier
 
 ast_lowering_this_not_async = this is not `async`
 
-ast_lowering_underscore_array_length_unstable =
-    using `_` for array lengths is unstable
-
 ast_lowering_underscore_expr_lhs_assign =
     in expressions, `_` can only be used on the left-hand side of an assignment
     .label = `_` not allowed here
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 3b99a653417..e74fd1db15b 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -48,7 +48,7 @@ use rustc_data_structures::sorted_map::SortedMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::spawn;
 use rustc_data_structures::tagged_ptr::TaggedRef;
-use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle, StashKey};
+use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle};
 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
 use rustc_hir::lints::DelayedLint;
@@ -60,7 +60,7 @@ use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
-use rustc_session::parse::{add_feature_diagnostics, feature_err};
+use rustc_session::parse::add_feature_diagnostics;
 use rustc_span::symbol::{Ident, Symbol, kw, sym};
 use rustc_span::{DUMMY_SP, DesugaringKind, Span};
 use smallvec::SmallVec;
@@ -2109,15 +2109,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // `ExprKind::Paren(ExprKind::Underscore)` and should also be lowered to `GenericArg::Infer`
         match c.value.peel_parens().kind {
             ExprKind::Underscore => {
-                if !self.tcx.features().generic_arg_infer() {
-                    feature_err(
-                        &self.tcx.sess,
-                        sym::generic_arg_infer,
-                        c.value.span,
-                        fluent_generated::ast_lowering_underscore_array_length_unstable,
-                    )
-                    .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
-                }
                 let ct_kind = hir::ConstArgKind::Infer(self.lower_span(c.value.span), ());
                 self.arena.alloc(hir::ConstArg { hir_id: self.lower_node_id(c.id), kind: ct_kind })
             }
diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index e9c4c255bce..cfae1b3ec98 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -6,13 +6,11 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 ar_archive_writer = "0.4.2"
-arrayvec = { version = "0.7", default-features = false }
 bitflags = "2.4.1"
 bstr = "1.11.3"
 # Pinned so `cargo update` bumps don't cause breakage. Please also update the
 # `cc` in `rustc_llvm` if you update the `cc` here.
 cc = "=1.2.16"
-either = "1.5.0"
 itertools = "0.12"
 pathdiff = "0.2.0"
 regex = "1.4"
diff --git a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs b/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
index f731613d67e..025f5fb54f4 100644
--- a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
@@ -317,7 +317,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let name = if bx.sess().fewer_names() {
             None
         } else {
-            Some(match whole_local_var.or(fallback_var.clone()) {
+            Some(match whole_local_var.or_else(|| fallback_var.clone()) {
                 Some(var) if var.name != sym::empty => var.name.to_string(),
                 _ => format!("{local:?}"),
             })
diff --git a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
index b805dc094e9..9f66457a740 100644
--- a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
@@ -205,7 +205,7 @@ fn prefix_and_suffix<'tcx>(
     let mut end = String::new();
     match asm_binary_format {
         BinaryFormat::Elf => {
-            let section = link_section.unwrap_or(format!(".text.{asm_name}"));
+            let section = link_section.unwrap_or_else(|| format!(".text.{asm_name}"));
 
             let progbits = match is_arm {
                 true => "%progbits",
@@ -239,7 +239,7 @@ fn prefix_and_suffix<'tcx>(
             }
         }
         BinaryFormat::MachO => {
-            let section = link_section.unwrap_or("__TEXT,__text".to_string());
+            let section = link_section.unwrap_or_else(|| "__TEXT,__text".to_string());
             writeln!(begin, ".pushsection {},regular,pure_instructions", section).unwrap();
             writeln!(begin, ".balign {align_bytes}").unwrap();
             write_linkage(&mut begin).unwrap();
@@ -256,7 +256,7 @@ fn prefix_and_suffix<'tcx>(
             }
         }
         BinaryFormat::Coff => {
-            let section = link_section.unwrap_or(format!(".text.{asm_name}"));
+            let section = link_section.unwrap_or_else(|| format!(".text.{asm_name}"));
             writeln!(begin, ".pushsection {},\"xr\"", section).unwrap();
             writeln!(begin, ".balign {align_bytes}").unwrap();
             write_linkage(&mut begin).unwrap();
@@ -273,7 +273,7 @@ fn prefix_and_suffix<'tcx>(
             }
         }
         BinaryFormat::Wasm => {
-            let section = link_section.unwrap_or(format!(".text.{asm_name}"));
+            let section = link_section.unwrap_or_else(|| format!(".text.{asm_name}"));
 
             writeln!(begin, ".section {section},\"\",@").unwrap();
             // wasm functions cannot be aligned, so skip
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index e9389ddf93b..99957c67708 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -1,9 +1,9 @@
 use std::fmt;
 
-use arrayvec::ArrayVec;
-use either::Either;
 use rustc_abi as abi;
-use rustc_abi::{Align, BackendRepr, FIRST_VARIANT, Primitive, Size, TagEncoding, Variants};
+use rustc_abi::{
+    Align, BackendRepr, FIRST_VARIANT, FieldIdx, Primitive, Size, TagEncoding, VariantIdx, Variants,
+};
 use rustc_middle::mir::interpret::{Pointer, Scalar, alloc_range};
 use rustc_middle::mir::{self, ConstValue};
 use rustc_middle::ty::Ty;
@@ -13,6 +13,7 @@ use rustc_session::config::OptLevel;
 use tracing::{debug, instrument};
 
 use super::place::{PlaceRef, PlaceValue};
+use super::rvalue::transmute_immediate;
 use super::{FunctionCx, LocalRef};
 use crate::common::IntPredicate;
 use crate::traits::*;
@@ -69,31 +70,6 @@ pub enum OperandValue<V> {
 }
 
 impl<V: CodegenObject> OperandValue<V> {
-    /// If this is ZeroSized/Immediate/Pair, return an array of the 0/1/2 values.
-    /// If this is Ref, return the place.
-    #[inline]
-    pub(crate) fn immediates_or_place(self) -> Either<ArrayVec<V, 2>, PlaceValue<V>> {
-        match self {
-            OperandValue::ZeroSized => Either::Left(ArrayVec::new()),
-            OperandValue::Immediate(a) => Either::Left(ArrayVec::from_iter([a])),
-            OperandValue::Pair(a, b) => Either::Left([a, b].into()),
-            OperandValue::Ref(p) => Either::Right(p),
-        }
-    }
-
-    /// Given an array of 0/1/2 immediate values, return ZeroSized/Immediate/Pair.
-    #[inline]
-    pub(crate) fn from_immediates(immediates: ArrayVec<V, 2>) -> Self {
-        let mut it = immediates.into_iter();
-        let Some(a) = it.next() else {
-            return OperandValue::ZeroSized;
-        };
-        let Some(b) = it.next() else {
-            return OperandValue::Immediate(a);
-        };
-        OperandValue::Pair(a, b)
-    }
-
     /// Treat this value as a pointer and return the data pointer and
     /// optional metadata as backend values.
     ///
@@ -595,6 +571,105 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
             }
         }
     }
+
+    /// Creates an incomplete operand containing the [`abi::Scalar`]s expected based
+    /// on the `layout` passed. This is for use with [`OperandRef::insert_field`]
+    /// later to set the necessary immediate(s).
+    ///
+    /// Returns `None` for `layout`s which cannot be built this way.
+    pub(crate) fn builder(
+        layout: TyAndLayout<'tcx>,
+    ) -> Option<OperandRef<'tcx, Result<V, abi::Scalar>>> {
+        let val = match layout.backend_repr {
+            BackendRepr::Memory { .. } if layout.is_zst() => OperandValue::ZeroSized,
+            BackendRepr::Scalar(s) => OperandValue::Immediate(Err(s)),
+            BackendRepr::ScalarPair(a, b) => OperandValue::Pair(Err(a), Err(b)),
+            BackendRepr::Memory { .. } | BackendRepr::SimdVector { .. } => return None,
+        };
+        Some(OperandRef { val, layout })
+    }
+}
+
+impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, Result<V, abi::Scalar>> {
+    pub(crate) fn insert_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
+        &mut self,
+        bx: &mut Bx,
+        v: VariantIdx,
+        f: FieldIdx,
+        operand: OperandRef<'tcx, V>,
+    ) {
+        let (expect_zst, is_zero_offset) = if let abi::FieldsShape::Primitive = self.layout.fields {
+            // The other branch looking at field layouts ICEs for primitives,
+            // so we need to handle them separately.
+            // Multiple fields is possible for cases such as aggregating
+            // a thin pointer, where the second field is the unit.
+            assert!(!self.layout.is_zst());
+            assert_eq!(v, FIRST_VARIANT);
+            let first_field = f == FieldIdx::ZERO;
+            (!first_field, first_field)
+        } else {
+            let variant_layout = self.layout.for_variant(bx.cx(), v);
+            let field_layout = variant_layout.field(bx.cx(), f.as_usize());
+            let field_offset = variant_layout.fields.offset(f.as_usize());
+            (field_layout.is_zst(), field_offset == Size::ZERO)
+        };
+
+        let mut update = |tgt: &mut Result<V, abi::Scalar>, src, from_scalar| {
+            let from_bty = bx.cx().type_from_scalar(from_scalar);
+            let to_scalar = tgt.unwrap_err();
+            let to_bty = bx.cx().type_from_scalar(to_scalar);
+            let imm = transmute_immediate(bx, src, from_scalar, from_bty, to_scalar, to_bty);
+            *tgt = Ok(imm);
+        };
+
+        match (operand.val, operand.layout.backend_repr) {
+            (OperandValue::ZeroSized, _) if expect_zst => {}
+            (OperandValue::Immediate(v), BackendRepr::Scalar(from_scalar)) => match &mut self.val {
+                OperandValue::Immediate(val @ Err(_)) if is_zero_offset => {
+                    update(val, v, from_scalar);
+                }
+                OperandValue::Pair(fst @ Err(_), _) if is_zero_offset => {
+                    update(fst, v, from_scalar);
+                }
+                OperandValue::Pair(_, snd @ Err(_)) if !is_zero_offset => {
+                    update(snd, v, from_scalar);
+                }
+                _ => bug!("Tried to insert {operand:?} into {v:?}.{f:?} of {self:?}"),
+            },
+            (OperandValue::Pair(a, b), BackendRepr::ScalarPair(from_sa, from_sb)) => {
+                match &mut self.val {
+                    OperandValue::Pair(fst @ Err(_), snd @ Err(_)) => {
+                        update(fst, a, from_sa);
+                        update(snd, b, from_sb);
+                    }
+                    _ => bug!("Tried to insert {operand:?} into {v:?}.{f:?} of {self:?}"),
+                }
+            }
+            _ => bug!("Unsupported operand {operand:?} inserting into {v:?}.{f:?} of {self:?}"),
+        }
+    }
+
+    /// After having set all necessary fields, this converts the
+    /// `OperandValue<Result<V, _>>` (as obtained from [`OperandRef::builder`])
+    /// to the normal `OperandValue<V>`.
+    ///
+    /// ICEs if any required fields were not set.
+    pub fn build(&self) -> OperandRef<'tcx, V> {
+        let OperandRef { val, layout } = *self;
+
+        let unwrap = |r: Result<V, abi::Scalar>| match r {
+            Ok(v) => v,
+            Err(_) => bug!("OperandRef::build called while fields are missing {self:?}"),
+        };
+
+        let val = match val {
+            OperandValue::ZeroSized => OperandValue::ZeroSized,
+            OperandValue::Immediate(v) => OperandValue::Immediate(unwrap(v)),
+            OperandValue::Pair(a, b) => OperandValue::Pair(unwrap(a), unwrap(b)),
+            OperandValue::Ref(_) => bug!(),
+        };
+        OperandRef { val, layout }
+    }
 }
 
 impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index b62ac89661f..e1d8b7546cf 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -1,7 +1,6 @@
 use std::assert_matches::assert_matches;
 
-use arrayvec::ArrayVec;
-use rustc_abi::{self as abi, FIRST_VARIANT, FieldIdx};
+use rustc_abi::{self as abi, FIRST_VARIANT};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
@@ -708,38 +707,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                 // `rvalue_creates_operand` has arranged that we only get here if
                 // we can build the aggregate immediate from the field immediates.
-                let mut inputs = ArrayVec::<Bx::Value, 2>::new();
-                let mut input_scalars = ArrayVec::<abi::Scalar, 2>::new();
-                for field_idx in layout.fields.index_by_increasing_offset() {
-                    let field_idx = FieldIdx::from_usize(field_idx);
-                    let op = self.codegen_operand(bx, &fields[field_idx]);
-                    let values = op.val.immediates_or_place().left_or_else(|p| {
-                        bug!("Field {field_idx:?} is {p:?} making {layout:?}");
-                    });
-                    let scalars = self.value_kind(op.layout).scalars().unwrap();
-                    assert_eq!(values.len(), scalars.len());
-                    inputs.extend(values);
-                    input_scalars.extend(scalars);
+                let Some(mut builder) = OperandRef::builder(layout) else {
+                    bug!("Cannot use type in operand builder: {layout:?}")
+                };
+                for (field_idx, field) in fields.iter_enumerated() {
+                    let op = self.codegen_operand(bx, field);
+                    builder.insert_field(bx, FIRST_VARIANT, field_idx, op);
                 }
 
-                let output_scalars = self.value_kind(layout).scalars().unwrap();
-                itertools::izip!(&mut inputs, input_scalars, output_scalars).for_each(
-                    |(v, in_s, out_s)| {
-                        if in_s != out_s {
-                            // We have to be really careful about bool here, because
-                            // `(bool,)` stays i1 but `Cell<bool>` becomes i8.
-                            *v = bx.from_immediate(*v);
-                            *v = bx.to_immediate_scalar(*v, out_s);
-                        }
-                    },
-                );
-
-                let val = OperandValue::from_immediates(inputs);
-                assert!(
-                    val.is_expected_variant_for_type(self.cx, layout),
-                    "Made wrong variant {val:?} for type {layout:?}",
-                );
-                OperandRef { val, layout }
+                builder.build()
             }
             mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
                 let operand = self.codegen_operand(bx, operand);
@@ -1082,10 +1058,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     mir::AggregateKind::Coroutine(..) | mir::AggregateKind::CoroutineClosure(..) => false,
                 };
                 allowed_kind && {
-                let ty = rvalue.ty(self.mir, self.cx.tcx());
-                let ty = self.monomorphize(ty);
+                    let ty = rvalue.ty(self.mir, self.cx.tcx());
+                    let ty = self.monomorphize(ty);
                     let layout = self.cx.spanned_layout_of(ty, span);
-                    !self.cx.is_backend_ref(layout)
+                    OperandRef::<Bx::Value>::builder(layout).is_some()
                 }
             }
         }
@@ -1129,23 +1105,12 @@ enum OperandValueKind {
     ZeroSized,
 }
 
-impl OperandValueKind {
-    fn scalars(self) -> Option<ArrayVec<abi::Scalar, 2>> {
-        Some(match self {
-            OperandValueKind::ZeroSized => ArrayVec::new(),
-            OperandValueKind::Immediate(a) => ArrayVec::from_iter([a]),
-            OperandValueKind::Pair(a, b) => [a, b].into(),
-            OperandValueKind::Ref => return None,
-        })
-    }
-}
-
 /// Transmutes one of the immediates from an [`OperandValue::Immediate`]
 /// or an [`OperandValue::Pair`] to an immediate of the target type.
 ///
 /// `to_backend_ty` must be the *non*-immediate backend type (so it will be
 /// `i8`, not `i1`, for `bool`-like types.)
-fn transmute_immediate<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+pub(super) fn transmute_immediate<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     bx: &mut Bx,
     mut imm: Bx::Value,
     from_scalar: abi::Scalar,
diff --git a/compiler/rustc_codegen_ssa/src/traits/type_.rs b/compiler/rustc_codegen_ssa/src/traits/type_.rs
index 70331b72353..dcd9e25b2c9 100644
--- a/compiler/rustc_codegen_ssa/src/traits/type_.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/type_.rs
@@ -1,4 +1,4 @@
-use rustc_abi::{AddressSpace, Float, Integer, Reg};
+use rustc_abi::{AddressSpace, Float, Integer, Primitive, Reg, Scalar};
 use rustc_middle::bug;
 use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, TyAndLayout};
@@ -84,6 +84,24 @@ pub trait DerivedTypeCodegenMethods<'tcx>:
     fn type_is_freeze(&self, ty: Ty<'tcx>) -> bool {
         ty.is_freeze(self.tcx(), self.typing_env())
     }
+
+    fn type_from_primitive(&self, p: Primitive) -> Self::Type {
+        use Primitive::*;
+        match p {
+            Int(i, _) => self.type_from_integer(i),
+            Float(f) => self.type_from_float(f),
+            Pointer(address_space) => self.type_ptr_ext(address_space),
+        }
+    }
+
+    fn type_from_scalar(&self, s: Scalar) -> Self::Type {
+        // `MaybeUninit` being `repr(transparent)` somewhat implies that the type
+        // of a scalar has to be the type of its primitive (which is true in LLVM,
+        // where noundef is a parameter attribute or metadata) but if we ever get
+        // a backend where that's no longer true, every use of this will need to
+        // to carefully scrutinized and re-evaluated.
+        self.type_from_primitive(s.primitive())
+    }
 }
 
 impl<'tcx, T> DerivedTypeCodegenMethods<'tcx> for T where
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index b1c185220f4..cfe0f4e5d6c 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -220,6 +220,8 @@ declare_features! (
     (accepted, fn_must_use, "1.27.0", Some(43302)),
     /// Allows capturing variables in scope using format_args!
     (accepted, format_args_capture, "1.58.0", Some(67984)),
+    /// Infer generic args for both consts and types.
+    (accepted, generic_arg_infer, "CURRENT_RUSTC_VERSION", Some(85077)),
     /// Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
     (accepted, generic_associated_types, "1.65.0", Some(44265)),
     /// Allows attributes on lifetime/type formal parameters in generics (RFC 1327).
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 5e42b919f9d..a7bc6207149 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -520,8 +520,6 @@ declare_features! (
     (unstable, frontmatter, "1.88.0", Some(136889)),
     /// Allows defining gen blocks and `gen fn`.
     (unstable, gen_blocks, "1.75.0", Some(117078)),
-    /// Infer generic args for both consts and types.
-    (unstable, generic_arg_infer, "1.55.0", Some(85077)),
     /// Allows non-trivial generic constants which have to have wfness manually propagated to callers
     (incomplete, generic_const_exprs, "1.56.0", Some(76560)),
     /// Allows generic parameters and where-clauses on free & associated const items.
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 141d96b57e5..902a2e15dff 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -452,13 +452,6 @@ fn infer_placeholder_type<'tcx>(
             if let Some(ty) = node.ty() {
                 visitor.visit_ty_unambig(ty);
             }
-            // If we have just one span, let's try to steal a const `_` feature error.
-            let try_steal_span = if !tcx.features().generic_arg_infer() && visitor.spans.len() == 1
-            {
-                visitor.spans.first().copied()
-            } else {
-                None
-            };
             // If we didn't find any infer tys, then just fallback to `span`.
             if visitor.spans.is_empty() {
                 visitor.spans.push(span);
@@ -489,15 +482,7 @@ fn infer_placeholder_type<'tcx>(
                 }
             }
 
-            if let Some(try_steal_span) = try_steal_span {
-                cx.dcx().try_steal_replace_and_emit_err(
-                    try_steal_span,
-                    StashKey::UnderscoreForArrayLengths,
-                    diag,
-                )
-            } else {
-                diag.emit()
-            }
+            diag.emit()
         });
     Ty::new_error(tcx, guar)
 }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
index 3a26b8331f8..8c7c3750865 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
@@ -8,7 +8,7 @@ use rustc_middle::ty::{
     self, GenericArgsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty,
 };
 use rustc_session::lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS;
-use rustc_span::{kw, sym};
+use rustc_span::kw;
 use smallvec::SmallVec;
 use tracing::{debug, instrument};
 
@@ -258,19 +258,6 @@ pub fn lower_generic_args<'tcx: 'a, 'a>(
                             GenericParamDefKind::Const { .. },
                             _,
                         ) => {
-                            if let GenericParamDefKind::Const { .. } = param.kind
-                                && let GenericArg::Infer(inf) = arg
-                                && !tcx.features().generic_arg_infer()
-                            {
-                                rustc_session::parse::feature_err(
-                                    tcx.sess,
-                                    sym::generic_arg_infer,
-                                    inf.span,
-                                    "const arguments cannot yet be inferred with `_`",
-                                )
-                                .emit();
-                            }
-
                             // We lower to an infer even when the feature gate is not enabled
                             // as it is useful for diagnostics to be able to see a `ConstKind::Infer`
                             args.push(ctx.provided_kind(&args, param, arg));
diff --git a/compiler/rustc_hir_typeck/src/op.rs b/compiler/rustc_hir_typeck/src/op.rs
index 7f7921b66b5..b9d24506986 100644
--- a/compiler/rustc_hir_typeck/src/op.rs
+++ b/compiler/rustc_hir_typeck/src/op.rs
@@ -706,7 +706,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .sess
                         .source_map()
                         .span_to_snippet(lhs_expr.span)
-                        .unwrap_or("_".to_string()),
+                        .unwrap_or_else(|_| "_".to_string()),
                 };
 
                 if op.span().can_be_used_for_suggestions() {
diff --git a/compiler/rustc_metadata/src/locator.rs b/compiler/rustc_metadata/src/locator.rs
index 79015aab5d3..259bcb1b96d 100644
--- a/compiler/rustc_metadata/src/locator.rs
+++ b/compiler/rustc_metadata/src/locator.rs
@@ -1196,7 +1196,7 @@ impl CrateError {
                             .opts
                             .crate_name
                             .clone()
-                            .unwrap_or("<unknown>".to_string()),
+                            .unwrap_or_else(|| "<unknown>".to_string()),
                         is_nightly_build: sess.is_nightly_build(),
                         profiler_runtime: Symbol::intern(&sess.opts.unstable_opts.profiler_runtime),
                         locator_triple: locator.triple,
@@ -1217,7 +1217,11 @@ impl CrateError {
                     crate_name,
                     add_info: String::new(),
                     missing_core,
-                    current_crate: sess.opts.crate_name.clone().unwrap_or("<unknown>".to_string()),
+                    current_crate: sess
+                        .opts
+                        .crate_name
+                        .clone()
+                        .unwrap_or_else(|| "<unknown>".to_string()),
                     is_nightly_build: sess.is_nightly_build(),
                     profiler_runtime: Symbol::intern(&sess.opts.unstable_opts.profiler_runtime),
                     locator_triple: sess.opts.target_triple.clone(),
diff --git a/compiler/rustc_metadata/src/native_libs.rs b/compiler/rustc_metadata/src/native_libs.rs
index 5cdeb8935f7..f10d71f4c65 100644
--- a/compiler/rustc_metadata/src/native_libs.rs
+++ b/compiler/rustc_metadata/src/native_libs.rs
@@ -705,7 +705,7 @@ impl<'tcx> Collector<'tcx> {
             .map_or(import_name_type, |ord| Some(PeImportNameType::Ordinal(ord)));
 
         DllImport {
-            name: codegen_fn_attrs.link_name.unwrap_or(self.tcx.item_name(item)),
+            name: codegen_fn_attrs.link_name.unwrap_or_else(|| self.tcx.item_name(item)),
             import_name_type,
             calling_convention,
             span,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 930d9fba433..3668f4e12f5 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1576,7 +1576,7 @@ rustc_queries! {
     query vtable_allocation(key: (Ty<'tcx>, Option<ty::ExistentialTraitRef<'tcx>>)) -> mir::interpret::AllocId {
         desc { |tcx| "vtable const allocation for <{} as {}>",
             key.0,
-            key.1.map(|trait_ref| format!("{trait_ref}")).unwrap_or("_".to_owned())
+            key.1.map(|trait_ref| format!("{trait_ref}")).unwrap_or_else(|| "_".to_owned())
         }
     }
 
diff --git a/compiler/rustc_passes/src/check_export.rs b/compiler/rustc_passes/src/check_export.rs
index b9a3849f32f..f8f489d7d06 100644
--- a/compiler/rustc_passes/src/check_export.rs
+++ b/compiler/rustc_passes/src/check_export.rs
@@ -53,11 +53,11 @@ impl<'tcx> ExportableItemCollector<'tcx> {
         let is_pub = visibilities.is_directly_public(def_id);
 
         if has_attr && !is_pub {
-            let vis = visibilities.effective_vis(def_id).cloned().unwrap_or(
+            let vis = visibilities.effective_vis(def_id).cloned().unwrap_or_else(|| {
                 EffectiveVisibility::from_vis(Visibility::Restricted(
                     self.tcx.parent_module_from_def_id(def_id).to_local_def_id(),
-                )),
-            );
+                ))
+            });
             let vis = vis.at_level(Level::Direct);
             let span = self.tcx.def_span(def_id);
 
diff --git a/compiler/rustc_session/src/filesearch.rs b/compiler/rustc_session/src/filesearch.rs
index def2cc97f06..4f8c3926207 100644
--- a/compiler/rustc_session/src/filesearch.rs
+++ b/compiler/rustc_session/src/filesearch.rs
@@ -209,10 +209,9 @@ pub fn get_or_default_sysroot() -> PathBuf {
         //
         // use `parent` twice to chop off the file name and then also the
         // directory containing the dll
-        let dir = dll.parent().and_then(|p| p.parent()).ok_or(format!(
-            "Could not move 2 levels upper using `parent()` on {}",
-            dll.display()
-        ))?;
+        let dir = dll.parent().and_then(|p| p.parent()).ok_or_else(|| {
+            format!("Could not move 2 levels upper using `parent()` on {}", dll.display())
+        })?;
 
         // if `dir` points to target's dir, move up to the sysroot
         let mut sysroot_dir = if dir.ends_with(crate::config::host_tuple()) {
@@ -265,5 +264,6 @@ pub fn get_or_default_sysroot() -> PathBuf {
         rustlib_path.exists().then_some(p)
     }
 
-    from_env_args_next().unwrap_or(default_from_rustc_driver_dll().expect("Failed finding sysroot"))
+    from_env_args_next()
+        .unwrap_or_else(|| default_from_rustc_driver_dll().expect("Failed finding sysroot"))
 }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
index b8207c4f816..5c669678ccc 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/region.rs
@@ -891,7 +891,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             (b'a'..=b'z')
                 .map(|c| format!("'{}", c as char))
                 .find(|candidate| !used_names.iter().any(|e| e.as_str() == candidate))
-                .unwrap_or("'lt".to_string())
+                .unwrap_or_else(|| "'lt".to_string())
         };
 
         let mut visitor = LifetimeReplaceVisitor {
diff --git a/compiler/rustc_trait_selection/src/traits/normalize.rs b/compiler/rustc_trait_selection/src/traits/normalize.rs
index 35a43b294ee..9e02ce32b21 100644
--- a/compiler/rustc_trait_selection/src/traits/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/normalize.rs
@@ -224,7 +224,7 @@ impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
             )
             .ok()
             .flatten()
-            .unwrap_or(proj.to_term(infcx.tcx));
+            .unwrap_or_else(|| proj.to_term(infcx.tcx));
 
             PlaceholderReplacer::replace_placeholders(
                 infcx,
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 9774263e4c9..d5222822461 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -896,10 +896,9 @@ fn variant_info_for_coroutine<'tcx>(
                     variant_size = variant_size.max(offset + field_layout.size);
                     FieldInfo {
                         kind: FieldKind::CoroutineLocal,
-                        name: field_name.unwrap_or(Symbol::intern(&format!(
-                            ".coroutine_field{}",
-                            local.as_usize()
-                        ))),
+                        name: field_name.unwrap_or_else(|| {
+                            Symbol::intern(&format!(".coroutine_field{}", local.as_usize()))
+                        }),
                         offset: offset.bytes(),
                         size: field_layout.size.bytes(),
                         align: field_layout.align.abi.bytes(),