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

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

A revival of rust-lang#124812.

Current status:

~~`./x.py b --stage 2` passes 🎉~~

`try` builds succeed 🎉 🎉 🎉

[first perf run](rust-lang#133502 (comment)) 👻

### crater

This does not detect hangs or memory issues.

| date | #crates | #regressions |
| ---- | ------- | ------------ |
| 2025.04.11 | 100 | 2 |
| 2025.04.11 | 1000 | 27 |
| 2025.04.17 | 10000 | 456 |
| 2025.04.18 | 10000 | 437 |
| 2025.04.24 | 10000 | 164 |
| 2025.04.26 | 10000 | 108 |
| 2025.04.28 | 10000 | 91 |
| 2025.05.01 | 10000 | 145 woops |
| 2025.05.03 | 624228[^1] |  1585 |

[^1]: a complete crater run

### in-flight changes

- rust-lang#139587
- rust-lang#140497
- rust-lang#124852, unsure whether I actually want to land this PR for now
- https://github.com/lcnr/rust/tree/opaque-type-method-call
- rust-lang#140260
- rust-lang#140375
- rust-lang#140405
- rust-lang#140496
- double recursion limit in the new solver

r? `@ghost`

Author: bors

compiler/rustc_borrowck/messages.ftl

@@ -156,12 +156,6 @@ borrowck_moved_due_to_usage_in_operator =
         *[false] operator
     }
 
-borrowck_opaque_type_lifetime_mismatch =
-    opaque type used twice with different lifetimes
-    .label = lifetime `{$arg}` used here
-    .prev_lifetime_label = lifetime `{$prev}` previously used here
-    .note = if all non-lifetime generic parameters are the same, but the lifetime parameters differ, it is not possible to differentiate the opaque types
-
 borrowck_partial_var_move_by_use_in_closure =
     variable {$is_partial ->
         [true] partially moved

compiler/rustc_borrowck/src/consumers.rs

@@ -15,7 +15,7 @@ pub use super::polonius::legacy::{
     RichLocation, RustcFacts,
 };
 pub use super::region_infer::RegionInferenceContext;
-use crate::{BorrowCheckRootCtxt, do_mir_borrowck};
+use crate::BorrowCheckRootCtxt;
 
 /// Options determining the output behavior of [`get_body_with_borrowck_facts`].
 ///
@@ -101,6 +101,6 @@ pub fn get_body_with_borrowck_facts(
     def_id: LocalDefId,
     options: ConsumerOptions,
 ) -> BodyWithBorrowckFacts<'_> {
-    let mut root_cx = BorrowCheckRootCtxt::new(tcx, def_id);
-    *do_mir_borrowck(&mut root_cx, def_id, Some(options)).1.unwrap()
+    let root_cx = BorrowCheckRootCtxt::new(tcx, def_id);
+    *root_cx.borrowck_root(Some(options)).1.unwrap()
 }

compiler/rustc_borrowck/src/dataflow.rs

@@ -1,7 +1,6 @@
 use std::fmt;
 
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::graph;
 use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::mir::{
     self, BasicBlock, Body, CallReturnPlaces, Location, Place, TerminatorEdges,
@@ -317,9 +316,8 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
             loans_out_of_scope_at_location: FxIndexMap::default(),
         };
         for (loan_idx, loan_data) in borrow_set.iter_enumerated() {
-            let issuing_region = loan_data.region;
             let loan_issued_at = loan_data.reserve_location;
-            prec.precompute_loans_out_of_scope(loan_idx, issuing_region, loan_issued_at);
+            prec.precompute_loans_out_of_scope(loan_idx, loan_issued_at);
         }
 
         prec.loans_out_of_scope_at_location
@@ -328,45 +326,7 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
     /// Loans are in scope while they are live: whether they are contained within any live region.
     /// In the location-insensitive analysis, a loan will be contained in a region if the issuing
     /// region can reach it in the subset graph. So this is a reachability problem.
-    fn precompute_loans_out_of_scope(
-        &mut self,
-        loan_idx: BorrowIndex,
-        issuing_region: RegionVid,
-        loan_issued_at: Location,
-    ) {
-        let sccs = self.regioncx.constraint_sccs();
-        let universal_regions = self.regioncx.universal_regions();
-
-        // The loop below was useful for the location-insensitive analysis but shouldn't be
-        // impactful in the location-sensitive case. It seems that it does, however, as without it a
-        // handful of tests fail. That likely means some liveness or outlives data related to choice
-        // regions is missing
-        // FIXME: investigate the impact of loans traversing applied member constraints and why some
-        // tests fail otherwise.
-        //
-        // We first handle the cases where the loan doesn't go out of scope, depending on the
-        // issuing region's successors.
-        for successor in graph::depth_first_search(&self.regioncx.region_graph(), issuing_region) {
-            // Via applied member constraints
-            //
-            // The issuing region can flow into the choice regions, and they are either:
-            // - placeholders or free regions themselves,
-            // - or also transitively outlive a free region.
-            //
-            // That is to say, if there are applied member constraints here, the loan escapes the
-            // function and cannot go out of scope. We could early return here.
-            //
-            // For additional insurance via fuzzing and crater, we verify that the constraint's min
-            // choice indeed escapes the function. In the future, we could e.g. turn this check into
-            // a debug assert and early return as an optimization.
-            let scc = sccs.scc(successor);
-            for constraint in self.regioncx.applied_member_constraints(scc) {
-                if universal_regions.is_universal_region(constraint.min_choice) {
-                    return;
-                }
-            }
-        }
-
+    fn precompute_loans_out_of_scope(&mut self, loan_idx: BorrowIndex, loan_issued_at: Location) {
         let first_block = loan_issued_at.block;
         let first_bb_data = &self.body.basic_blocks[first_block];
 

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -23,7 +23,6 @@ use rustc_trait_selection::error_reporting::infer::nice_region_error::{
     self, HirTraitObjectVisitor, NiceRegionError, TraitObjectVisitor, find_anon_type,
     find_param_with_region, suggest_adding_lifetime_params,
 };
-use rustc_trait_selection::error_reporting::infer::region::unexpected_hidden_region_diagnostic;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{Obligation, ObligationCtxt};
 use tracing::{debug, instrument, trace};
@@ -84,9 +83,6 @@ impl<'tcx> RegionErrors<'tcx> {
         let guar = self.1.sess.dcx().delayed_bug(format!("{val:?}"));
         self.0.push((val, guar));
     }
-    pub(crate) fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
     pub(crate) fn into_iter(
         self,
     ) -> impl Iterator<Item = (RegionErrorKind<'tcx>, ErrorGuaranteed)> {
@@ -108,18 +104,6 @@ pub(crate) enum RegionErrorKind<'tcx> {
     /// A generic bound failure for a type test (`T: 'a`).
     TypeTestError { type_test: TypeTest<'tcx> },
 
-    /// An unexpected hidden region for an opaque type.
-    UnexpectedHiddenRegion {
-        /// The span for the member constraint.
-        span: Span,
-        /// The hidden type.
-        hidden_ty: Ty<'tcx>,
-        /// The opaque type.
-        key: ty::OpaqueTypeKey<'tcx>,
-        /// The unexpected region.
-        member_region: ty::Region<'tcx>,
-    },
-
     /// Higher-ranked subtyping error.
     BoundUniversalRegionError {
         /// The placeholder free region.
@@ -312,9 +296,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         // buffered in the `MirBorrowckCtxt`.
 
         let mut outlives_suggestion = OutlivesSuggestionBuilder::default();
-        let mut last_unexpected_hidden_region: Option<(Span, Ty<'_>, ty::OpaqueTypeKey<'tcx>)> =
-            None;
-
         for (nll_error, _) in nll_errors.into_iter() {
             match nll_error {
                 RegionErrorKind::TypeTestError { type_test } => {
@@ -364,30 +345,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     }
                 }
 
-                RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, key, member_region } => {
-                    let named_ty =
-                        self.regioncx.name_regions_for_member_constraint(self.infcx.tcx, hidden_ty);
-                    let named_key =
-                        self.regioncx.name_regions_for_member_constraint(self.infcx.tcx, key);
-                    let named_region = self
-                        .regioncx
-                        .name_regions_for_member_constraint(self.infcx.tcx, member_region);
-                    let diag = unexpected_hidden_region_diagnostic(
-                        self.infcx,
-                        self.mir_def_id(),
-                        span,
-                        named_ty,
-                        named_region,
-                        named_key,
-                    );
-                    if last_unexpected_hidden_region != Some((span, named_ty, named_key)) {
-                        self.buffer_error(diag);
-                        last_unexpected_hidden_region = Some((span, named_ty, named_key));
-                    } else {
-                        diag.delay_as_bug();
-                    }
-                }
-
                 RegionErrorKind::BoundUniversalRegionError {
                     longer_fr,
                     placeholder,