Auto merge of #77557 - Dylan-DPC:rollup-aib9ptp, r=Dylan-DPC

Rollup of 11 pull requests

Successful merges:

 - #75853 (Use more intra-doc-links in `core::fmt`)
 - #75928 (Remove trait_selection error message in specific case)
 - #76329 (Add check for doc alias attribute at crate level)
 - #77219 (core::global_allocator docs link to std::alloc::GlobalAlloc)
 - #77395 (BTreeMap: admit the existence of leaf edges in comments)
 - #77407 (Improve build-manifest to work with the improved promote-release)
 - #77426 (Include scope id in SocketAddrV6::Display)
 - #77439 (Fix missing diagnostic span for `impl Trait` with const generics, and add various tests for `min_const_generics` and `const_generics`)
 - #77471 (BTreeMap: refactoring around edges, missed spots)
 - #77512 (Allow `Abort` terminators in all const-contexts)
 - #77514 (Replace some once(x).chain(once(y)) with [x, y] IntoIter)

Failed merges:

r? `@ghost`

17 files changed, 110 insertions, 52 deletions

diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 5cd0a56d524..cd018ae1204 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -581,7 +581,7 @@ declare_features! (
     /// Allows `if let` guard in match arms.
     (active, if_let_guard, "1.47.0", Some(51114), None),
 
-    /// Allows non trivial generic constants which have to be manually propageted upwards.
+    /// Allows non-trivial generic constants which have to be manually propageted upwards.
     (active, const_evaluatable_checked, "1.48.0", Some(76560), None),
 
     /// Allows basic arithmetic on floating point types in a `const fn`.
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index 96fde48d96c..62b12542877 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -341,9 +341,7 @@ impl<T> PerNS<Option<T>> {
 
     /// Returns an iterator over the items which are `Some`.
     pub fn present_items(self) -> impl Iterator<Item = T> {
-        use std::iter::once;
-
-        once(self.type_ns).chain(once(self.value_ns)).chain(once(self.macro_ns)).filter_map(|it| it)
+        IntoIter::new([self.type_ns, self.value_ns, self.macro_ns]).filter_map(|it| it)
     }
 }
 
diff --git a/compiler/rustc_hir/src/target.rs b/compiler/rustc_hir/src/target.rs
index 1efc8bc3124..fd6a312ef3a 100644
--- a/compiler/rustc_hir/src/target.rs
+++ b/compiler/rustc_hir/src/target.rs
@@ -9,13 +9,13 @@ use crate::{Item, ItemKind, TraitItem, TraitItemKind};
 
 use std::fmt::{self, Display};
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub enum MethodKind {
     Trait { body: bool },
     Inherent,
 }
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub enum Target {
     ExternCrate,
     Use,
diff --git a/compiler/rustc_mir/src/transform/check_consts/ops.rs b/compiler/rustc_mir/src/transform/check_consts/ops.rs
index 32e233e337d..9a1b77e994d 100644
--- a/compiler/rustc_mir/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_mir/src/transform/check_consts/ops.rs
@@ -42,18 +42,6 @@ pub trait NonConstOp: std::fmt::Debug {
 }
 
 #[derive(Debug)]
-pub struct Abort;
-impl NonConstOp for Abort {
-    fn status_in_item(&self, ccx: &ConstCx<'_, '_>) -> Status {
-        mcf_status_in_item(ccx)
-    }
-
-    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
-        mcf_build_error(ccx, span, "abort is not stable in const fn")
-    }
-}
-
-#[derive(Debug)]
 pub struct FloatingPointOp;
 impl NonConstOp for FloatingPointOp {
     fn status_in_item(&self, ccx: &ConstCx<'_, '_>) -> Status {
diff --git a/compiler/rustc_mir/src/transform/check_consts/validation.rs b/compiler/rustc_mir/src/transform/check_consts/validation.rs
index 4e714bfeed3..94806116eaf 100644
--- a/compiler/rustc_mir/src/transform/check_consts/validation.rs
+++ b/compiler/rustc_mir/src/transform/check_consts/validation.rs
@@ -434,11 +434,13 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
     fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &BasicBlockData<'tcx>) {
         trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
 
-        // Just as the old checker did, we skip const-checking basic blocks on the unwind path.
-        // These blocks often drop locals that would otherwise be returned from the function.
+        // We don't const-check basic blocks on the cleanup path since we never unwind during
+        // const-eval: a panic causes an immediate compile error. In other words, cleanup blocks
+        // are unreachable during const-eval.
         //
-        // FIXME: This shouldn't be unsound since a panic at compile time will cause a compiler
-        // error anyway, but maybe we should do more here?
+        // We can't be more conservative (e.g., by const-checking cleanup blocks anyways) because
+        // locals that would never be dropped during normal execution are sometimes dropped during
+        // unwinding, which means backwards-incompatible live-drop errors.
         if block.is_cleanup {
             return;
         }
@@ -874,12 +876,16 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
             }
 
             TerminatorKind::InlineAsm { .. } => self.check_op(ops::InlineAsm),
-            TerminatorKind::Abort => self.check_op(ops::Abort),
 
             TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => {
                 self.check_op(ops::Generator(hir::GeneratorKind::Gen))
             }
 
+            TerminatorKind::Abort => {
+                // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
+                span_bug!(self.span, "`Abort` terminator outside of cleanup block")
+            }
+
             TerminatorKind::Assert { .. }
             | TerminatorKind::FalseEdge { .. }
             | TerminatorKind::FalseUnwind { .. }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index b52216c45ce..59955b27334 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -13,12 +13,14 @@ use rustc_errors::{pluralize, struct_span_err};
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
-use rustc_hir::{self, FnSig, ForeignItem, ForeignItemKind, HirId, Item, ItemKind, TraitItem};
+use rustc_hir::{
+    self, FnSig, ForeignItem, ForeignItemKind, HirId, Item, ItemKind, TraitItem, CRATE_HIR_ID,
+};
 use rustc_hir::{MethodKind, Target};
 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::sym;
-use rustc_span::Span;
+use rustc_span::symbol::{sym, Symbol};
+use rustc_span::{Span, DUMMY_SP};
 
 pub(crate) fn target_from_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -333,6 +335,17 @@ impl CheckAttrVisitor<'tcx> {
                                 .emit();
                             return false;
                         }
+                        if CRATE_HIR_ID == hir_id {
+                            self.tcx
+                                .sess
+                                .struct_span_err(
+                                    meta.span(),
+                                    "`#![doc(alias = \"...\")]` isn't allowed as a crate \
+                                     level attribute",
+                                )
+                                .emit();
+                            return false;
+                        }
                     }
                 }
             }
@@ -808,9 +821,46 @@ fn is_c_like_enum(item: &Item<'_>) -> bool {
     }
 }
 
+fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
+    const ATTRS_TO_CHECK: &[Symbol] = &[
+        sym::macro_export,
+        sym::repr,
+        sym::path,
+        sym::automatically_derived,
+        sym::start,
+        sym::main,
+    ];
+
+    for attr in attrs {
+        for attr_to_check in ATTRS_TO_CHECK {
+            if tcx.sess.check_name(attr, *attr_to_check) {
+                tcx.sess
+                    .struct_span_err(
+                        attr.span,
+                        &format!(
+                            "`{}` attribute cannot be used at crate level",
+                            attr_to_check.to_ident_string()
+                        ),
+                    )
+                    .emit();
+            }
+        }
+    }
+}
+
 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
     tcx.hir()
         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
+    if module_def_id.is_top_level_module() {
+        CheckAttrVisitor { tcx }.check_attributes(
+            CRATE_HIR_ID,
+            tcx.hir().krate_attrs(),
+            &DUMMY_SP,
+            Target::Mod,
+            None,
+        );
+        check_invalid_crate_level_attr(tcx, tcx.hir().krate_attrs());
+    }
 }
 
 pub(crate) fn provide(providers: &mut Providers) {
diff --git a/compiler/rustc_passes/src/entry.rs b/compiler/rustc_passes/src/entry.rs
index 8aa6e7936be..e87adb378e7 100644
--- a/compiler/rustc_passes/src/entry.rs
+++ b/compiler/rustc_passes/src/entry.rs
@@ -78,29 +78,38 @@ fn entry_fn(tcx: TyCtxt<'_>, cnum: CrateNum) -> Option<(LocalDefId, EntryFnType)
 // Beware, this is duplicated in `librustc_builtin_macros/test_harness.rs`
 // (with `ast::Item`), so make sure to keep them in sync.
 fn entry_point_type(sess: &Session, item: &Item<'_>, at_root: bool) -> EntryPointType {
-    match item.kind {
-        ItemKind::Fn(..) => {
-            if sess.contains_name(&item.attrs, sym::start) {
-                EntryPointType::Start
-            } else if sess.contains_name(&item.attrs, sym::main) {
-                EntryPointType::MainAttr
-            } else if item.ident.name == sym::main {
-                if at_root {
-                    // This is a top-level function so can be `main`.
-                    EntryPointType::MainNamed
-                } else {
-                    EntryPointType::OtherMain
-                }
-            } else {
-                EntryPointType::None
-            }
+    if sess.contains_name(&item.attrs, sym::start) {
+        EntryPointType::Start
+    } else if sess.contains_name(&item.attrs, sym::main) {
+        EntryPointType::MainAttr
+    } else if item.ident.name == sym::main {
+        if at_root {
+            // This is a top-level function so can be `main`.
+            EntryPointType::MainNamed
+        } else {
+            EntryPointType::OtherMain
         }
-        _ => EntryPointType::None,
+    } else {
+        EntryPointType::None
     }
 }
 
+fn throw_attr_err(sess: &Session, span: Span, attr: &str) {
+    sess.struct_span_err(span, &format!("`{}` attribute can only be used on functions", attr))
+        .emit();
+}
+
 fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
     match entry_point_type(&ctxt.session, item, at_root) {
+        EntryPointType::None => (),
+        _ if !matches!(item.kind, ItemKind::Fn(..)) => {
+            if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::start) {
+                throw_attr_err(&ctxt.session, attr.span, "start");
+            }
+            if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::main) {
+                throw_attr_err(&ctxt.session, attr.span, "main");
+            }
+        }
         EntryPointType::MainNamed => {
             if ctxt.main_fn.is_none() {
                 ctxt.main_fn = Some((item.hir_id, item.span));
@@ -137,7 +146,6 @@ fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
                     .emit();
             }
         }
-        EntryPointType::None => (),
     }
 }
 
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 612bc3e7491..e3cf6d12bd5 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -469,7 +469,7 @@ impl<'a> Resolver<'a> {
             ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
                 let mut err = self.session.struct_span_err(
                     span,
-                    "generic parameters must not be used inside of non trivial constant values",
+                    "generic parameters must not be used inside of non-trivial constant values",
                 );
                 err.span_label(
                     span,
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 283db1404d0..fe8f5926385 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -218,7 +218,7 @@ enum ResolutionError<'a> {
     ParamInTyOfConstParam(Symbol),
     /// constant values inside of type parameter defaults must not depend on generic parameters.
     ParamInAnonConstInTyDefault(Symbol),
-    /// generic parameters must not be used inside of non trivial constant values.
+    /// generic parameters must not be used inside of non-trivial constant values.
     ///
     /// This error is only emitted when using `min_const_generics`.
     ParamInNonTrivialAnonConst { name: Symbol, is_type: bool },
diff --git a/compiler/rustc_session/src/lint/builtin.rs b/compiler/rustc_session/src/lint/builtin.rs
index 0cc97fb4541..3e899e00d11 100644
--- a/compiler/rustc_session/src/lint/builtin.rs
+++ b/compiler/rustc_session/src/lint/builtin.rs
@@ -518,7 +518,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![macro_export]
+    /// #![ignore]
     /// ```
     ///
     /// {{produces}}
diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs
index ddeab340f38..406e8936e6e 100644
--- a/compiler/rustc_trait_selection/src/lib.rs
+++ b/compiler/rustc_trait_selection/src/lib.rs
@@ -11,6 +11,7 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(array_value_iter)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(drain_filter)]
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 90a8d9634ae..967374ffdc2 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -1907,6 +1907,11 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
                 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
                 let ty = parent_trait_ref.skip_binder().self_ty();
+                if parent_trait_ref.references_error() {
+                    err.cancel();
+                    return;
+                }
+
                 err.note(&format!("required because it appears within the type `{}`", ty));
                 obligated_types.push(ty);
 
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 2f2ac9f094d..8fc14cb2997 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -24,6 +24,7 @@ use rustc_span::symbol::Symbol;
 use rustc_span::Span;
 use smallvec::SmallVec;
 
+use std::array;
 use std::iter;
 
 pub use crate::traits::{MethodViolationCode, ObjectSafetyViolation};
@@ -652,8 +653,7 @@ fn receiver_is_dispatchable<'tcx>(
         let caller_bounds: Vec<Predicate<'tcx>> = param_env
             .caller_bounds()
             .iter()
-            .chain(iter::once(unsize_predicate))
-            .chain(iter::once(trait_predicate))
+            .chain(array::IntoIter::new([unsize_predicate, trait_predicate]))
             .collect();
 
         ty::ParamEnv::new(tcx.intern_predicates(&caller_bounds), param_env.reveal())
diff --git a/compiler/rustc_typeck/src/astconv/generics.rs b/compiler/rustc_typeck/src/astconv/generics.rs
index b54de1d0916..b867798c76c 100644
--- a/compiler/rustc_typeck/src/astconv/generics.rs
+++ b/compiler/rustc_typeck/src/astconv/generics.rs
@@ -562,7 +562,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 .args
                 .iter()
                 .filter_map(|arg| match arg {
-                    GenericArg::Type(_) => Some(arg.span()),
+                    GenericArg::Type(_) | GenericArg::Const(_) => Some(arg.span()),
                     _ => None,
                 })
                 .collect::<Vec<_>>();
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index 46b8b2e14c7..170ca2ce744 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -35,8 +35,8 @@ use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
 use rustc_trait_selection::traits::wf::object_region_bounds;
 
 use smallvec::SmallVec;
+use std::array;
 use std::collections::BTreeSet;
-use std::iter;
 use std::slice;
 
 #[derive(Debug)]
@@ -1346,7 +1346,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
 
             let is_equality = is_equality();
-            let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
+            let bounds = array::IntoIter::new([bound, bound2]).chain(matching_candidates);
             let mut err = if is_equality.is_some() {
                 // More specific Error Index entry.
                 struct_span_err!(
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 9aca112a914..1f4f40fca9b 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -222,6 +222,7 @@ impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
                 hir::GenericParamKind::Const { .. } => {
                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
                     self.tcx.ensure().type_of(def_id);
+                    // FIXME(const_generics:defaults)
                 }
             }
         }
diff --git a/compiler/rustc_typeck/src/lib.rs b/compiler/rustc_typeck/src/lib.rs
index 21fb92ec889..7efda54fbe0 100644
--- a/compiler/rustc_typeck/src/lib.rs
+++ b/compiler/rustc_typeck/src/lib.rs
@@ -56,6 +56,7 @@ This API is completely unstable and subject to change.
 */
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(array_value_iter)]
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]