Auto merge of rust-lang#120251 - matthiaskrgr:rollup-gttrw68, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#119664 (Fix tty detection for msys2's `/dev/ptmx`)
 - rust-lang#120104 (never_patterns: Count `!` bindings as diverging)
 - rust-lang#120109 (Move cmath into `sys`)
 - rust-lang#120143 (Consolidate logic around resolving built-in coroutine trait impls)
 - rust-lang#120159 (Track `verbose` and `verbose_internals`)
 - rust-lang#120216 (Fix a `trimmed_def_paths` assertion failure.)
 - rust-lang#120220 (Document `Token{Stream,Tree}::Display` more thoroughly.)
 - rust-lang#120233 (Revert stabilization of trait_upcasting feature)

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

Author: bors

Diff for: compiler/rustc_feature/src/accepted.rs

@@ -339,9 +339,6 @@ declare_features! (
     /// Allows `#[track_caller]` to be used which provides
     /// accurate caller location reporting during panic (RFC 2091).
     (accepted, track_caller, "1.46.0", Some(47809)),
-    /// Allows dyn upcasting trait objects via supertraits.
-    /// Dyn upcasting is casting, e.g., `dyn Foo -> dyn Bar` where `Foo: Bar`.
-    (accepted, trait_upcasting, "1.76.0", Some(65991)),
     /// Allows #[repr(transparent)] on univariant enums (RFC 2645).
     (accepted, transparent_enums, "1.42.0", Some(60405)),
     /// Allows indexing tuples.

Diff for: compiler/rustc_feature/src/unstable.rs

@@ -584,6 +584,9 @@ declare_features! (
     (unstable, thread_local, "1.0.0", Some(29594)),
     /// Allows defining `trait X = A + B;` alias items.
     (unstable, trait_alias, "1.24.0", Some(41517)),
+    /// Allows dyn upcasting trait objects via supertraits.
+    /// Dyn upcasting is casting, e.g., `dyn Foo -> dyn Bar` where `Foo: Bar`.
+    (unstable, trait_upcasting, "1.56.0", Some(65991)),
     /// Allows for transmuting between arrays with sizes that contain generic consts.
     (unstable, transmute_generic_consts, "1.70.0", Some(109929)),
     /// Allows #[repr(transparent)] on unions (RFC 2645).

Diff for: compiler/rustc_hir/src/lang_items.rs

@@ -213,8 +213,11 @@ language_item_table! {
     Iterator,                sym::iterator,            iterator_trait,             Target::Trait,          GenericRequirement::Exact(0);
     Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
     AsyncIterator,           sym::async_iterator,      async_iterator_trait,       Target::Trait,          GenericRequirement::Exact(0);
+
     CoroutineState,          sym::coroutine_state,     coroutine_state,            Target::Enum,           GenericRequirement::None;
     Coroutine,               sym::coroutine,           coroutine_trait,            Target::Trait,          GenericRequirement::Minimum(1);
+    CoroutineResume,         sym::coroutine_resume,    coroutine_resume,           Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
+
     Unpin,                   sym::unpin,               unpin_trait,                Target::Trait,          GenericRequirement::None;
     Pin,                     sym::pin,                 pin_type,                   Target::Struct,         GenericRequirement::None;
 

Diff for: compiler/rustc_hir_typeck/src/check.rs

@@ -2,8 +2,7 @@ use std::cell::RefCell;
 
 use crate::coercion::CoerceMany;
 use crate::gather_locals::GatherLocalsVisitor;
-use crate::CoroutineTypes;
-use crate::FnCtxt;
+use crate::{CoroutineTypes, Diverges, FnCtxt};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::intravisit::Visitor;
@@ -76,6 +75,12 @@ pub(super) fn check_fn<'a, 'tcx>(
         let ty: Option<&hir::Ty<'_>> = try { inputs_hir?.get(idx)? };
         let ty_span = ty.map(|ty| ty.span);
         fcx.check_pat_top(param.pat, param_ty, ty_span, None, None);
+        if param.pat.is_never_pattern() {
+            fcx.function_diverges_because_of_empty_arguments.set(Diverges::Always {
+                span: param.pat.span,
+                custom_note: Some("any code following a never pattern is unreachable"),
+            });
+        }
 
         // Check that argument is Sized.
         if !params_can_be_unsized {
@@ -105,6 +110,7 @@ pub(super) fn check_fn<'a, 'tcx>(
         hir::FnRetTy::Return(ty) => ty.span,
     };
     fcx.require_type_is_sized(declared_ret_ty, return_or_body_span, traits::SizedReturnType);
+    fcx.is_whole_body.set(true);
     fcx.check_return_expr(body.value, false);
 
     // Finalize the return check by taking the LUB of the return types

Diff for: compiler/rustc_hir_typeck/src/coercion.rs

@@ -625,6 +625,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         )];
 
         let mut has_unsized_tuple_coercion = false;
+        let mut has_trait_upcasting_coercion = None;
 
         // Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
         // emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where
@@ -692,6 +693,13 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                     // these here and emit a feature error if coercion doesn't fail
                     // due to another reason.
                     match impl_source {
+                        traits::ImplSource::Builtin(
+                            BuiltinImplSource::TraitUpcasting { .. },
+                            _,
+                        ) => {
+                            has_trait_upcasting_coercion =
+                                Some((trait_pred.self_ty(), trait_pred.trait_ref.args.type_at(1)));
+                        }
                         traits::ImplSource::Builtin(BuiltinImplSource::TupleUnsizing, _) => {
                             has_unsized_tuple_coercion = true;
                         }
@@ -702,6 +710,21 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             }
         }
 
+        if let Some((sub, sup)) = has_trait_upcasting_coercion
+            && !self.tcx().features().trait_upcasting
+        {
+            // Renders better when we erase regions, since they're not really the point here.
+            let (sub, sup) = self.tcx.erase_regions((sub, sup));
+            let mut err = feature_err(
+                &self.tcx.sess,
+                sym::trait_upcasting,
+                self.cause.span,
+                format!("cannot cast `{sub}` to `{sup}`, trait upcasting coercion is experimental"),
+            );
+            err.note(format!("required when coercing `{source}` into `{target}`"));
+            err.emit();
+        }
+
         if has_unsized_tuple_coercion && !self.tcx.features().unsized_tuple_coercion {
             feature_err(
                 &self.tcx.sess,

Diff for: compiler/rustc_hir_typeck/src/expr.rs

@@ -208,10 +208,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // without the final expr (e.g. `try { return; }`). We don't want to generate an
         // unreachable_code lint for it since warnings for autogenerated code are confusing.
         let is_try_block_generated_unit_expr = match expr.kind {
-            ExprKind::Call(_, args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
-                args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
+            ExprKind::Call(_, [arg]) => {
+                expr.span.is_desugaring(DesugaringKind::TryBlock)
+                    && arg.span.is_desugaring(DesugaringKind::TryBlock)
             }
-
             _ => false,
         };
 
@@ -220,9 +220,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
         }
 
-        // Hide the outer diverging and has_errors flags.
+        // Whether a past expression diverges doesn't affect typechecking of this expression, so we
+        // reset `diverges` while checking `expr`.
         let old_diverges = self.diverges.replace(Diverges::Maybe);
 
+        if self.is_whole_body.replace(false) {
+            // If this expression is the whole body and the function diverges because of its
+            // arguments, we check this here to ensure the body is considered to diverge.
+            self.diverges.set(self.function_diverges_because_of_empty_arguments.get())
+        };
+
         let ty = ensure_sufficient_stack(|| match &expr.kind {
             hir::ExprKind::Path(
                 qpath @ (hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)),

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1471,6 +1471,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Type check a `let` statement.
     pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
         self.check_decl(local.into());
+        if local.pat.is_never_pattern() {
+            self.diverges.set(Diverges::Always {
+                span: local.pat.span,
+                custom_note: Some("any code following a never pattern is unreachable"),
+            });
+        }
     }
 
     pub fn check_stmt(&self, stmt: &'tcx hir::Stmt<'tcx>) {

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -103,6 +103,13 @@ pub struct FnCtxt<'a, 'tcx> {
     /// the diverges flag is set to something other than `Maybe`.
     pub(super) diverges: Cell<Diverges>,
 
+    /// If one of the function arguments is a never pattern, this counts as diverging code. This
+    /// affect typechecking of the function body.
+    pub(super) function_diverges_because_of_empty_arguments: Cell<Diverges>,
+
+    /// Whether the currently checked node is the whole body of the function.
+    pub(super) is_whole_body: Cell<bool>,
+
     pub(super) enclosing_breakables: RefCell<EnclosingBreakables<'tcx>>,
 
     pub(super) inh: &'a Inherited<'tcx>,
@@ -124,6 +131,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ret_coercion_span: Cell::new(None),
             coroutine_types: None,
             diverges: Cell::new(Diverges::Maybe),
+            function_diverges_because_of_empty_arguments: Cell::new(Diverges::Maybe),
+            is_whole_body: Cell::new(false),
             enclosing_breakables: RefCell::new(EnclosingBreakables {
                 stack: Vec::new(),
                 by_id: Default::default(),

Diff for: compiler/rustc_interface/src/tests.rs

@@ -98,6 +98,7 @@ fn assert_same_hash(x: &Options, y: &Options) {
     assert_same_clone(y);
 }
 
+#[track_caller]
 fn assert_different_hash(x: &Options, y: &Options) {
     assert_ne!(x.dep_tracking_hash(true), y.dep_tracking_hash(true));
     assert_ne!(x.dep_tracking_hash(false), y.dep_tracking_hash(false));
@@ -713,7 +714,6 @@ fn test_unstable_options_tracking_hash() {
     untracked!(unpretty, Some("expanded".to_string()));
     untracked!(unstable_options, true);
     untracked!(validate_mir, true);
-    untracked!(verbose_internals, true);
     untracked!(write_long_types_to_disk, false);
     // tidy-alphabetical-end
 
@@ -845,6 +845,7 @@ fn test_unstable_options_tracking_hash() {
         };
     }
     tracked_no_crate_hash!(no_codegen, true);
+    tracked_no_crate_hash!(verbose_internals, true);
 }
 
 #[test]

Diff for: compiler/rustc_lint/src/deref_into_dyn_supertrait.rs

@@ -5,13 +5,17 @@ use crate::{
 
 use rustc_hir as hir;
 use rustc_middle::ty;
+use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_span::sym;
 use rustc_trait_selection::traits::supertraits;
 
 declare_lint! {
     /// The `deref_into_dyn_supertrait` lint is output whenever there is a use of the
     /// `Deref` implementation with a `dyn SuperTrait` type as `Output`.
     ///
+    /// These implementations will become shadowed when the `trait_upcasting` feature is stabilized.
+    /// The `deref` functions will no longer be called implicitly, so there might be behavior change.
+    ///
     /// ### Example
     ///
     /// ```rust,compile_fail
@@ -40,10 +44,15 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// The implicit dyn upcasting coercion take priority over those `Deref` impls.
+    /// The dyn upcasting coercion feature adds new coercion rules, taking priority
+    /// over certain other coercion rules, which will cause some behavior change.
     pub DEREF_INTO_DYN_SUPERTRAIT,
     Warn,
-    "`Deref` implementation usage with a supertrait trait object for output are shadow by implicit coercion",
+    "`Deref` implementation usage with a supertrait trait object for output might be shadowed in the future",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
+        reference: "issue #89460 <https://github.com/rust-lang/rust/issues/89460>",
+    };
 }
 
 declare_lint_pass!(DerefIntoDynSupertrait => [DEREF_INTO_DYN_SUPERTRAIT]);

Diff for: compiler/rustc_lint/src/lib.rs

@@ -35,6 +35,7 @@
 #![feature(iter_intersperse)]
 #![feature(iter_order_by)]
 #![feature(let_chains)]
+#![cfg_attr(not(bootstrap), feature(trait_upcasting))]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]

Diff for: compiler/rustc_lint/src/lints.rs

@@ -532,7 +532,6 @@ pub enum BuiltinSpecialModuleNameUsed {
 // deref_into_dyn_supertrait.rs
 #[derive(LintDiagnostic)]
 #[diag(lint_supertrait_as_deref_target)]
-#[help]
 pub struct SupertraitAsDerefTarget<'a> {
     pub self_ty: Ty<'a>,
     pub supertrait_principal: PolyExistentialTraitRef<'a>,

Diff for: compiler/rustc_middle/src/lib.rs

@@ -49,6 +49,7 @@
 #![feature(associated_type_bounds)]
 #![feature(rustc_attrs)]
 #![feature(control_flow_enum)]
+#![cfg_attr(not(bootstrap), feature(trait_upcasting))]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(try_reserve_kind)]

Diff for: compiler/rustc_middle/src/ty/instance.rs

@@ -3,6 +3,7 @@ use crate::ty::print::{FmtPrinter, Printer};
 use crate::ty::{self, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
 use crate::ty::{EarlyBinder, GenericArgs, GenericArgsRef, TypeVisitableExt};
 use rustc_errors::ErrorGuaranteed;
+use rustc_hir as hir;
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::lang_items::LangItem;
@@ -11,6 +12,7 @@ use rustc_macros::HashStable;
 use rustc_middle::ty::normalize_erasing_regions::NormalizationError;
 use rustc_span::Symbol;
 
+use std::assert_matches::assert_matches;
 use std::fmt;
 
 /// A monomorphized `InstanceDef`.
@@ -572,6 +574,54 @@ impl<'tcx> Instance<'tcx> {
         Some(Instance { def, args })
     }
 
+    pub fn try_resolve_item_for_coroutine(
+        tcx: TyCtxt<'tcx>,
+        trait_item_id: DefId,
+        trait_id: DefId,
+        rcvr_args: ty::GenericArgsRef<'tcx>,
+    ) -> Option<Instance<'tcx>> {
+        let ty::Coroutine(coroutine_def_id, args) = *rcvr_args.type_at(0).kind() else {
+            return None;
+        };
+        let coroutine_kind = tcx.coroutine_kind(coroutine_def_id).unwrap();
+
+        let lang_items = tcx.lang_items();
+        let coroutine_callable_item = if Some(trait_id) == lang_items.future_trait() {
+            assert_matches!(
+                coroutine_kind,
+                hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)
+            );
+            hir::LangItem::FuturePoll
+        } else if Some(trait_id) == lang_items.iterator_trait() {
+            assert_matches!(
+                coroutine_kind,
+                hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _)
+            );
+            hir::LangItem::IteratorNext
+        } else if Some(trait_id) == lang_items.async_iterator_trait() {
+            assert_matches!(
+                coroutine_kind,
+                hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _)
+            );
+            hir::LangItem::AsyncIteratorPollNext
+        } else if Some(trait_id) == lang_items.coroutine_trait() {
+            assert_matches!(coroutine_kind, hir::CoroutineKind::Coroutine(_));
+            hir::LangItem::CoroutineResume
+        } else {
+            return None;
+        };
+
+        if tcx.lang_items().get(coroutine_callable_item) == Some(trait_item_id) {
+            Some(Instance { def: ty::InstanceDef::Item(coroutine_def_id), args: args })
+        } else {
+            // All other methods should be defaulted methods of the built-in trait.
+            // This is important for `Iterator`'s combinators, but also useful for
+            // adding future default methods to `Future`, for instance.
+            debug_assert!(tcx.defaultness(trait_item_id).has_value());
+            Some(Instance::new(trait_item_id, rcvr_args))
+        }
+    }
+
     /// Depending on the kind of `InstanceDef`, the MIR body associated with an
     /// instance is expressed in terms of the generic parameters of `self.def_id()`, and in other
     /// cases the MIR body is expressed in terms of the types found in the substitution array.

Diff for: compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3072,8 +3072,6 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
 /// See also [`DelayDm`](rustc_error_messages::DelayDm) and [`with_no_trimmed_paths!`].
 // this is pub to be able to intra-doc-link it
 pub fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> DefIdMap<Symbol> {
-    assert!(tcx.sess.opts.trimmed_def_paths);
-
     // Trimming paths is expensive and not optimized, since we expect it to only be used for error
     // reporting.
     //

Diff for: compiler/rustc_session/src/options.rs

@@ -224,7 +224,7 @@ top_level_options!(
         working_dir: RealFileName [TRACKED],
         color: ColorConfig [UNTRACKED],
 
-        verbose: bool [UNTRACKED],
+        verbose: bool [TRACKED_NO_CRATE_HASH],
     }
 );
 
@@ -1986,7 +1986,7 @@ written to standard error output)"),
     validate_mir: bool = (false, parse_bool, [UNTRACKED],
         "validate MIR after each transformation"),
     #[rustc_lint_opt_deny_field_access("use `Session::verbose_internals` instead of this field")]
-    verbose_internals: bool = (false, parse_bool, [UNTRACKED],
+    verbose_internals: bool = (false, parse_bool, [TRACKED_NO_CRATE_HASH],
         "in general, enable more debug printouts (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::verify_llvm_ir` instead of this field")]
     verify_llvm_ir: bool = (false, parse_bool, [TRACKED],

Diff for: compiler/rustc_span/src/symbol.rs

@@ -600,6 +600,7 @@ symbols! {
         core_panic_macro,
         coroutine,
         coroutine_clone,
+        coroutine_resume,
         coroutine_state,
         coroutines,
         cosf32,