Auto merge of #133502 - lcnr:rust4, r=<try>

[DO NOT MERGE] bootstrap with `-Znext-solver=globally`

A revival of #124812.

Current status:

`./x.py b --stage 2` passes 🎉

### commits

- #133501
- #133493
- 9456bfe and b21b116 reimplement candidate preference based on #132325, not yet a separate PR
- c3ef9cd is a rebased version of #125334, unsure whether I actually want to land this PR for now
- #133517
* #133518
* #133519
* #133520
* #133521
* #133524

r? `@ghost`

Author: bors

compiler/rustc_borrowck/src/type_check/canonical.rs

@@ -7,6 +7,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, Upcast};
 use rustc_span::Span;
 use rustc_span::def_id::DefId;
+use rustc_trait_selection::solve::NoSolution;
 use rustc_trait_selection::traits::ObligationCause;
 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
 use rustc_trait_selection::traits::query::type_op::{self, TypeOpOutput};
@@ -177,6 +178,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         if self.infcx.next_trait_solver() {
             let body = self.body;
             let param_env = self.infcx.param_env;
+            // FIXME: Make this into a real type op?
             self.fully_perform_op(
                 location.to_locations(),
                 ConstraintCategory::Boring,
@@ -213,6 +215,40 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         }
     }
 
+    #[instrument(skip(self), level = "debug")]
+    pub(super) fn structurally_resolve(
+        &mut self,
+        ty: Ty<'tcx>,
+        location: impl NormalizeLocation,
+    ) -> Ty<'tcx> {
+        if self.infcx.next_trait_solver() {
+            let body = self.body;
+            let param_env = self.infcx.param_env;
+            // FIXME: Make this into a real type op?
+            self.fully_perform_op(
+                location.to_locations(),
+                ConstraintCategory::Boring,
+                CustomTypeOp::new(
+                    |ocx| {
+                        ocx.structurally_normalize(
+                            &ObligationCause::misc(
+                                location.to_locations().span(body),
+                                body.source.def_id().expect_local(),
+                            ),
+                            param_env,
+                            ty,
+                        )
+                        .map_err(|_| NoSolution)
+                    },
+                    "normalizing struct tail",
+                ),
+            )
+            .unwrap_or_else(|guar| Ty::new_error(self.tcx(), guar))
+        } else {
+            self.normalize(ty, location)
+        }
+    }
+
     #[instrument(skip(self), level = "debug")]
     pub(super) fn ascribe_user_type(
         &mut self,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1075,7 +1075,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 proj,
                 |this, field, ()| {
                     let ty = this.field_ty(tcx, field);
-                    self.normalize(ty, locations)
+                    self.structurally_resolve(ty, locations)
                 },
                 |_, _| unreachable!(),
             );

compiler/rustc_hir_analysis/src/check/check.rs

@@ -322,8 +322,12 @@ fn check_opaque_meets_bounds<'tcx>(
     };
     let param_env = tcx.param_env(defining_use_anchor);
 
-    // FIXME(#132279): This should eventually use the already defined hidden types.
-    let infcx = tcx.infer_ctxt().build(TypingMode::analysis_in_body(tcx, defining_use_anchor));
+    // FIXME(#132279): Once `PostBorrowckAnalysis` is supported in the old solver, this branch should be removed.
+    let infcx = tcx.infer_ctxt().build(if tcx.next_trait_solver_globally() {
+        TypingMode::post_borrowck_analysis(tcx, defining_use_anchor)
+    } else {
+        TypingMode::analysis_in_body(tcx, defining_use_anchor)
+    });
     let ocx = ObligationCtxt::new_with_diagnostics(&infcx);
 
     let args = match origin {
@@ -417,7 +421,11 @@ fn check_opaque_meets_bounds<'tcx>(
     let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
     ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env)?;
 
-    if let hir::OpaqueTyOrigin::FnReturn { .. } | hir::OpaqueTyOrigin::AsyncFn { .. } = origin {
+    if infcx.next_trait_solver() {
+        Ok(())
+    } else if let hir::OpaqueTyOrigin::FnReturn { .. } | hir::OpaqueTyOrigin::AsyncFn { .. } =
+        origin
+    {
         // HACK: this should also fall through to the hidden type check below, but the original
         // implementation had a bug where equivalent lifetimes are not identical. This caused us
         // to reject existing stable code that is otherwise completely fine. The real fix is to

compiler/rustc_hir_typeck/src/expectation.rs

@@ -1,5 +1,5 @@
 use rustc_middle::ty::{self, Ty};
-use rustc_span::Span;
+use rustc_span::{DUMMY_SP, Span};
 
 use super::Expectation::*;
 use super::FnCtxt;
@@ -102,7 +102,7 @@ impl<'a, 'tcx> Expectation<'tcx> {
     /// such a constraint, if it exists.
     pub(super) fn only_has_type(self, fcx: &FnCtxt<'a, 'tcx>) -> Option<Ty<'tcx>> {
         match self {
-            ExpectHasType(ty) => Some(fcx.resolve_vars_if_possible(ty)),
+            ExpectHasType(ty) => Some(fcx.try_structurally_resolve_type(DUMMY_SP, ty)),
             NoExpectation | ExpectCastableToType(_) | ExpectRvalueLikeUnsized(_) => None,
         }
     }

compiler/rustc_hir_typeck/src/expr.rs

@@ -68,7 +68,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // While we don't allow *arbitrary* coercions here, we *do* allow
         // coercions from ! to `expected`.
-        if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
+        if self.try_structurally_resolve_type(expr.span, ty).is_never()
+            && self.expr_guaranteed_to_constitute_read_for_never(expr)
+        {
             if let Some(_) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
                 let reported = self.dcx().span_delayed_bug(
                     expr.span,
@@ -274,7 +276,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // unless it's a place expression that isn't being read from, in which case
         // diverging would be unsound since we may never actually read the `!`.
         // e.g. `let _ = *never_ptr;` with `never_ptr: *const !`.
-        if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
+        if self.try_structurally_resolve_type(expr.span, ty).is_never()
+            && self.expr_guaranteed_to_constitute_read_for_never(expr)
+        {
             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
         }
 

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -1574,7 +1574,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         // Thus we need to prevent them from trying to match the `&_` autoref
                         // candidates that get created for `&self` trait methods.
                         ty::Alias(ty::Opaque, alias_ty)
-                            if self.infcx.can_define_opaque_ty(alias_ty.def_id)
+                            if !self.next_trait_solver()
+                                && self.infcx.can_define_opaque_ty(alias_ty.def_id)
                                 && !xform_self_ty.is_ty_var() =>
                         {
                             return ProbeResult::NoMatch;
@@ -1642,6 +1643,25 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 }
             }
 
+            // In the new solver, check the well-formedness of the return type.
+            // This emulates, in a way, the predicates that fall out of
+            // normalizing the return type in the old solver.
+            //
+            // We alternatively could check the predicates of the method itself hold,
+            // but we intentionally do not do this in the old solver b/c of cycles,
+            // and doing it in the new solver would be stronger. This should be fixed
+            // in the future, since it likely leads to much better method winnowing.
+            if let Some(xform_ret_ty) = xform_ret_ty
+                && self.infcx.next_trait_solver()
+            {
+                ocx.register_obligation(traits::Obligation::new(
+                    self.tcx,
+                    cause.clone(),
+                    self.param_env,
+                    ty::ClauseKind::WellFormed(xform_ret_ty.into()),
+                ));
+            }
+
             // Evaluate those obligations to see if they might possibly hold.
             for error in ocx.select_where_possible() {
                 result = ProbeResult::NoMatch;

compiler/rustc_hir_typeck/src/upvar.rs

@@ -1802,7 +1802,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut is_mutbl = bm.1;
 
         for pointer_ty in place.deref_tys() {
-            match pointer_ty.kind() {
+            match self.structurally_resolve_type(self.tcx.hir().span(var_hir_id), pointer_ty).kind()
+            {
                 // We don't capture derefs of raw ptrs
                 ty::RawPtr(_, _) => unreachable!(),
 
@@ -1816,7 +1817,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Dereferencing a box doesn't change mutability
                 ty::Adt(def, ..) if def.is_box() => {}
 
-                unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
+                unexpected_ty => span_bug!(
+                    self.tcx.hir().span(var_hir_id),
+                    "deref of unexpected pointer type {:?}",
+                    unexpected_ty
+                ),
             }
         }
 

compiler/rustc_infer/src/infer/context.rs

@@ -7,7 +7,7 @@ use rustc_middle::ty::relate::combine::PredicateEmittingRelation;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::{DUMMY_SP, ErrorGuaranteed};
 
-use super::{BoundRegionConversionTime, InferCtxt, SubregionOrigin};
+use super::{BoundRegionConversionTime, InferCtxt, RegionVariableOrigin, SubregionOrigin};
 
 impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
     type Interner = TyCtxt<'tcx>;
@@ -87,6 +87,10 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
         self.inner.borrow_mut().unwrap_region_constraints().opportunistic_resolve_var(self.tcx, vid)
     }
 
+    fn next_region_infer(&self) -> ty::Region<'tcx> {
+        self.next_region_var(RegionVariableOrigin::MiscVariable(DUMMY_SP))
+    }
+
     fn next_ty_infer(&self) -> Ty<'tcx> {
         self.next_ty_var(DUMMY_SP)
     }

compiler/rustc_infer/src/infer/mod.rs

@@ -990,11 +990,17 @@ impl<'tcx> InferCtxt<'tcx> {
 
     #[inline(always)]
     pub fn can_define_opaque_ty(&self, id: impl Into<DefId>) -> bool {
+        debug_assert!(!self.next_trait_solver());
         match self.typing_mode() {
             TypingMode::Analysis { defining_opaque_types } => {
                 id.into().as_local().is_some_and(|def_id| defining_opaque_types.contains(&def_id))
             }
-            TypingMode::Coherence | TypingMode::PostAnalysis => false,
+            // FIXME(#132279): This function is quite weird in post-analysis
+            // and post-borrowck analysis mode. We may need to modify its uses
+            // to support PostBorrowckAnalysis in the old solver as well.
+            TypingMode::Coherence
+            | TypingMode::PostBorrowckAnalysis { .. }
+            | TypingMode::PostAnalysis => false,
         }
     }
 
@@ -1276,15 +1282,16 @@ impl<'tcx> InferCtxt<'tcx> {
     /// using canonicalization or carrying this inference context around.
     pub fn typing_env(&self, param_env: ty::ParamEnv<'tcx>) -> ty::TypingEnv<'tcx> {
         let typing_mode = match self.typing_mode() {
-            ty::TypingMode::Coherence => ty::TypingMode::Coherence,
             // FIXME(#132279): This erases the `defining_opaque_types` as it isn't possible
             // to handle them without proper canonicalization. This means we may cause cycle
             // errors and fail to reveal opaques while inside of bodies. We should rename this
             // function and require explicit comments on all use-sites in the future.
             ty::TypingMode::Analysis { defining_opaque_types: _ } => {
                 TypingMode::non_body_analysis()
             }
-            ty::TypingMode::PostAnalysis => ty::TypingMode::PostAnalysis,
+            mode @ (ty::TypingMode::Coherence
+            | ty::TypingMode::PostBorrowckAnalysis { .. }
+            | ty::TypingMode::PostAnalysis) => mode,
         };
         ty::TypingEnv { typing_mode, param_env }
     }

compiler/rustc_infer/src/infer/opaque_types/mod.rs

@@ -98,6 +98,7 @@ impl<'tcx> InferCtxt<'tcx> {
         span: Span,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, TypeError<'tcx>> {
+        debug_assert!(!self.next_trait_solver());
         let process = |a: Ty<'tcx>, b: Ty<'tcx>| match *a.kind() {
             ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
@@ -546,7 +547,9 @@ impl<'tcx> InferCtxt<'tcx> {
                     );
                 }
             }
-            ty::TypingMode::PostAnalysis => bug!("insert hidden type post-analysis"),
+            mode @ (ty::TypingMode::PostBorrowckAnalysis { .. } | ty::TypingMode::PostAnalysis) => {
+                bug!("insert hidden type in {mode:?}")
+            }
         }
 
         Ok(())

compiler/rustc_middle/src/ty/context.rs

@@ -632,6 +632,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     fn opaque_types_defined_by(self, defining_anchor: LocalDefId) -> Self::DefiningOpaqueTypes {
         self.opaque_types_defined_by(defining_anchor)
     }
+
+    fn fold_regions<T: TypeFoldable<TyCtxt<'tcx>>>(
+        self,
+        value: T,
+        f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
+    ) -> T {
+        self.fold_regions(value, f)
+    }
 }
 
 macro_rules! bidirectional_lang_item_map {

compiler/rustc_middle/src/ty/fold.rs

@@ -55,14 +55,11 @@ where
 
 impl<'tcx> TyCtxt<'tcx> {
     /// Folds the escaping and free regions in `value` using `f`.
-    pub fn fold_regions<T>(
+    pub fn fold_regions<T: TypeFoldable<TyCtxt<'tcx>>>(
         self,
         value: T,
         mut f: impl FnMut(ty::Region<'tcx>, ty::DebruijnIndex) -> ty::Region<'tcx>,
-    ) -> T
-    where
-        T: TypeFoldable<TyCtxt<'tcx>>,
-    {
+    ) -> T {
         value.fold_with(&mut RegionFolder::new(self, &mut f))
     }
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -23,6 +23,11 @@ pub use adt::*;
 pub use assoc::*;
 pub use generic_args::{GenericArgKind, TermKind, *};
 pub use generics::*;
+// Can't use a glob import here as it would cause
+// ambiguity when importing the actual types implementing
+// the inherent traits from this module.
+#[allow(rustc::non_glob_import_of_type_ir_inherent)]
+use inherent::SliceLike;
 pub use intrinsic::IntrinsicDef;
 use rustc_abi::{Align, FieldIdx, Integer, IntegerType, ReprFlags, ReprOptions, VariantIdx};
 use rustc_ast::expand::StrippedCfgItem;
@@ -970,7 +975,7 @@ pub struct ParamEnv<'tcx> {
 }
 
 impl<'tcx> rustc_type_ir::inherent::ParamEnv<TyCtxt<'tcx>> for ParamEnv<'tcx> {
-    fn caller_bounds(self) -> impl IntoIterator<Item = ty::Clause<'tcx>> {
+    fn caller_bounds(self) -> impl SliceLike<Item = ty::Clause<'tcx>> {
         self.caller_bounds()
     }
 }