Auto merge of rust-lang#126023 - amandasystems:you-dropped-this-again, r=nikomatsakis

Remove confusing `use_polonius` flag and do less cloning

The `use_polonius` flag is both redundant and confusing since every function it's propagated to also checks if `all_facts` is `Some`, the true test of whether to generate Polonius facts for Polonius or for external consumers. This PR makes that path clearer by simply doing away with the argument and handling the logic in precisely two places: where facts are populated (check for `Some`), and where `all_facts` are initialised. It also delays some statements until after that check to avoid the miniscule performance penalty of executing them when Polonius is disabled.

This also addresses `@lqd's` concern in rust-lang#125652 by reducing the size of what is cloned out of Polonius facts to just the facts being added, as opposed to the entire vector of potential inputs, and added descriptive comments.

*Reviewer note*: the comments in `add_extra_drop_facts` should be inspected by a reviewer, in particular the one on [L#259](https://github.com/rust-lang/rust/compare/master...amandasystems:you-dropped-this-again?expand=1#diff-aa727290e6670264df2face84f012897878e11a70e9c8b156543cfcd9619bac3R259) in this PR, which should be trivial for someone with the right background knowledge to address.

I also included some lints I found on the way there that I couldn't help myself from addressing.

Author: bors

compiler/rustc_borrowck/src/borrow_set.rs

@@ -126,7 +126,7 @@ impl<'tcx> BorrowSet<'tcx> {
     ) -> Self {
         let mut visitor = GatherBorrows {
             tcx,
-            body: body,
+            body,
             location_map: Default::default(),
             activation_map: Default::default(),
             local_map: Default::default(),

compiler/rustc_borrowck/src/borrowck_errors.rs

@@ -213,7 +213,7 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
             via(msg_old),
         );
 
-        if msg_new == "" {
+        if msg_new.is_empty() {
             // If `msg_new` is empty, then this isn't a borrow of a union field.
             err.span_label(span, format!("{kind_new} borrow occurs here"));
             err.span_label(old_span, format!("{kind_old} borrow occurs here"));

compiler/rustc_borrowck/src/dataflow.rs

@@ -43,9 +43,9 @@ impl<'mir, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'mir, 'tcx> {
     }
 
     fn reset_to_block_entry(&self, state: &mut Self::FlowState, block: BasicBlock) {
-        state.borrows.clone_from(&self.borrows.entry_set_for_block(block));
-        state.uninits.clone_from(&self.uninits.entry_set_for_block(block));
-        state.ever_inits.clone_from(&self.ever_inits.entry_set_for_block(block));
+        state.borrows.clone_from(self.borrows.entry_set_for_block(block));
+        state.uninits.clone_from(self.uninits.entry_set_for_block(block));
+        state.ever_inits.clone_from(self.ever_inits.entry_set_for_block(block));
     }
 
     fn reconstruct_before_statement_effect(

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -895,7 +895,6 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             for alias_ty in alias_tys {
                 if alias_ty.span.desugaring_kind().is_some() {
                     // Skip `async` desugaring `impl Future`.
-                    ()
                 }
                 if let TyKind::TraitObject(_, lt, _) = alias_ty.kind {
                     if lt.ident.name == kw::Empty {

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -519,7 +519,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     }
 
                     // Otherwise, let's descend into the referent types.
-                    search_stack.push((*referent_ty, &referent_hir_ty.ty));
+                    search_stack.push((*referent_ty, referent_hir_ty.ty));
                 }
 
                 // Match up something like `Foo<'1>`
@@ -558,7 +558,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 }
 
                 (ty::RawPtr(mut_ty, _), hir::TyKind::Ptr(mut_hir_ty)) => {
-                    search_stack.push((*mut_ty, &mut_hir_ty.ty));
+                    search_stack.push((*mut_ty, mut_hir_ty.ty));
                 }
 
                 _ => {
@@ -652,7 +652,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         let upvar_index = self.regioncx.get_upvar_index_for_region(self.infcx.tcx, fr)?;
         let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
             self.infcx.tcx,
-            &self.upvars,
+            self.upvars,
             upvar_index,
         );
         let region_name = self.synthesize_region_name();
@@ -717,7 +717,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                             .output;
                         span = output.span();
                         if let hir::FnRetTy::Return(ret) = output {
-                            hir_ty = Some(self.get_future_inner_return_ty(*ret));
+                            hir_ty = Some(self.get_future_inner_return_ty(ret));
                         }
                         " of async function"
                     }
@@ -958,7 +958,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
         {
             let (upvar_name, upvar_span) = self.regioncx.get_upvar_name_and_span_for_region(
                 self.infcx.tcx,
-                &self.upvars,
+                self.upvars,
                 upvar_index,
             );
             let region_name = self.synthesize_region_name();

compiler/rustc_borrowck/src/nll.rs

@@ -114,7 +114,6 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
             move_data,
             elements,
             upvars,
-            polonius_input,
         );
 
     // Create the region inference context, taking ownership of the

compiler/rustc_borrowck/src/polonius/mod.rs

@@ -43,8 +43,8 @@ pub(crate) fn emit_facts<'tcx>(
     emit_universal_region_facts(
         all_facts,
         borrow_set,
-        &universal_regions,
-        &universal_region_relations,
+        universal_regions,
+        universal_region_relations,
     );
     emit_cfg_and_loan_kills_facts(all_facts, tcx, location_table, body, borrow_set);
     emit_loan_invalidations_facts(all_facts, tcx, location_table, body, borrow_set);

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -344,7 +344,7 @@ fn sccs_info<'tcx>(infcx: &BorrowckInferCtxt<'tcx>, sccs: &ConstraintSccs) {
 
     for (reg_var_idx, scc_idx) in sccs.scc_indices().iter().enumerate() {
         let reg_var = ty::RegionVid::from_usize(reg_var_idx);
-        let origin = var_to_origin.get(&reg_var).unwrap_or_else(|| &RegionCtxt::Unknown);
+        let origin = var_to_origin.get(&reg_var).unwrap_or(&RegionCtxt::Unknown);
         components[scc_idx.as_usize()].insert((reg_var, *origin));
     }
 
@@ -2216,7 +2216,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // #114907 where this happens via liveness and dropck outlives results.
         // Therefore, we return a default value in case that happens, which should at worst emit a
         // suboptimal error, instead of the ICE.
-        self.universe_causes.get(&universe).cloned().unwrap_or_else(|| UniverseInfo::other())
+        self.universe_causes.get(&universe).cloned().unwrap_or_else(UniverseInfo::other)
     }
 
     /// Tries to find the terminator of the loop in which the region 'r' resides.

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -418,9 +418,7 @@ fn check_opaque_type_parameter_valid<'tcx>(
             let opaque_param = opaque_generics.param_at(i, tcx);
             let kind = opaque_param.kind.descr();
 
-            if let Err(guar) = opaque_env.param_is_error(i) {
-                return Err(guar);
-            }
+            opaque_env.param_is_error(i)?;
 
             return Err(tcx.dcx().emit_err(NonGenericOpaqueTypeParam {
                 ty: arg,

compiler/rustc_borrowck/src/type_check/liveness/mod.rs

@@ -12,9 +12,7 @@ use rustc_mir_dataflow::ResultsCursor;
 use std::rc::Rc;
 
 use crate::{
-    constraints::OutlivesConstraintSet,
-    facts::{AllFacts, AllFactsExt},
-    region_infer::values::LivenessValues,
+    constraints::OutlivesConstraintSet, region_infer::values::LivenessValues,
     universal_regions::UniversalRegions,
 };
 
@@ -38,7 +36,6 @@ pub(super) fn generate<'mir, 'tcx>(
     elements: &Rc<DenseLocationMap>,
     flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
-    use_polonius: bool,
 ) {
     debug!("liveness::generate");
 
@@ -49,11 +46,8 @@ pub(super) fn generate<'mir, 'tcx>(
     );
     let (relevant_live_locals, boring_locals) =
         compute_relevant_live_locals(typeck.tcx(), &free_regions, body);
-    let facts_enabled = use_polonius || AllFacts::enabled(typeck.tcx());
 
-    if facts_enabled {
-        polonius::populate_access_facts(typeck, body, move_data);
-    };
+    polonius::populate_access_facts(typeck, body, move_data);
 
     trace::trace(
         typeck,