Auto merge of #91799 - matthiaskrgr:rollup-b38xx6i, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #83174 (Suggest using a temporary variable to fix borrowck errors)
 - #89734 (Point at capture points for non-`'static` reference crossing a `yield` point)
 - #90270 (Make `Borrow` and `BorrowMut` impls `const`)
 - #90741 (Const `Option::cloned`)
 - #91548 (Add spin_loop hint for RISC-V architecture)
 - #91721 (Minor improvements to `future::join!`'s implementation)

Failed merges:

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

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -368,6 +368,7 @@ fn try_extract_error_from_fulfill_cx<'tcx>(
                 error_region,
                 cause.clone(),
                 placeholder_region,
+                vec![],
             ),
         ),
         (Some(error_region), _) => NiceRegionError::new(

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -15,16 +15,18 @@ use rustc_span::symbol::sym;
 use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
 use rustc_trait_selection::infer::InferCtxtExt;
 
+use crate::borrow_set::TwoPhaseActivation;
 use crate::borrowck_errors;
 
+use crate::diagnostics::find_all_local_uses;
 use crate::{
     borrow_set::BorrowData, diagnostics::Instance, prefixes::IsPrefixOf,
     InitializationRequiringAction, MirBorrowckCtxt, PrefixSet, WriteKind,
 };
 
 use super::{
-    explain_borrow::BorrowExplanation, FnSelfUseKind, IncludingDowncast, RegionName,
-    RegionNameSource, UseSpans,
+    explain_borrow::{BorrowExplanation, LaterUseKind},
+    FnSelfUseKind, IncludingDowncast, RegionName, RegionNameSource, UseSpans,
 };
 
 #[derive(Debug)]
@@ -768,9 +770,92 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             Some((issued_span, span)),
         );
 
+        self.suggest_using_local_if_applicable(
+            &mut err,
+            location,
+            (place, span),
+            gen_borrow_kind,
+            issued_borrow,
+            explanation,
+        );
+
         err
     }
 
+    #[instrument(level = "debug", skip(self, err))]
+    fn suggest_using_local_if_applicable(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        location: Location,
+        (place, span): (Place<'tcx>, Span),
+        gen_borrow_kind: BorrowKind,
+        issued_borrow: &BorrowData<'tcx>,
+        explanation: BorrowExplanation,
+    ) {
+        let used_in_call =
+            matches!(explanation, BorrowExplanation::UsedLater(LaterUseKind::Call, _call_span, _));
+        if !used_in_call {
+            debug!("not later used in call");
+            return;
+        }
+
+        let outer_call_loc =
+            if let TwoPhaseActivation::ActivatedAt(loc) = issued_borrow.activation_location {
+                loc
+            } else {
+                issued_borrow.reserve_location
+            };
+        let outer_call_stmt = self.body.stmt_at(outer_call_loc);
+
+        let inner_param_location = location;
+        let Some(inner_param_stmt) = self.body.stmt_at(inner_param_location).left() else {
+            debug!("`inner_param_location` {:?} is not for a statement", inner_param_location);
+            return;
+        };
+        let Some(&inner_param) = inner_param_stmt.kind.as_assign().map(|(p, _)| p) else {
+            debug!(
+                "`inner_param_location` {:?} is not for an assignment: {:?}",
+                inner_param_location, inner_param_stmt
+            );
+            return;
+        };
+        let inner_param_uses = find_all_local_uses::find(self.body, inner_param.local);
+        let Some((inner_call_loc,inner_call_term)) = inner_param_uses.into_iter().find_map(|loc| {
+            let Either::Right(term) = self.body.stmt_at(loc) else {
+                debug!("{:?} is a statement, so it can't be a call", loc);
+                return None;
+            };
+            let TerminatorKind::Call { args, .. } = &term.kind else {
+                debug!("not a call: {:?}", term);
+                return None;
+            };
+            debug!("checking call args for uses of inner_param: {:?}", args);
+            if args.contains(&Operand::Move(inner_param)) {
+                Some((loc,term))
+            } else {
+                None
+            }
+        }) else {
+            debug!("no uses of inner_param found as a by-move call arg");
+            return;
+        };
+        debug!("===> outer_call_loc = {:?}, inner_call_loc = {:?}", outer_call_loc, inner_call_loc);
+
+        let inner_call_span = inner_call_term.source_info.span;
+        let outer_call_span = outer_call_stmt.either(|s| s.source_info, |t| t.source_info).span;
+        if outer_call_span == inner_call_span || !outer_call_span.contains(inner_call_span) {
+            // FIXME: This stops the suggestion in some cases where it should be emitted.
+            //        Fix the spans for those cases so it's emitted correctly.
+            debug!(
+                "outer span {:?} does not strictly contain inner span {:?}",
+                outer_call_span, inner_call_span
+            );
+            return;
+        }
+        err.span_help(inner_call_span, "try adding a local storing this argument...");
+        err.span_help(outer_call_span, "...and then using that local as the argument to this call");
+    }
+
     fn suggest_split_at_mut_if_applicable(
         &self,
         err: &mut DiagnosticBuilder<'_>,

compiler/rustc_borrowck/src/diagnostics/find_all_local_uses.rs

@@ -0,0 +1,26 @@
+use std::collections::BTreeSet;
+
+use rustc_middle::mir::visit::{PlaceContext, Visitor};
+use rustc_middle::mir::{Body, Local, Location};
+
+/// Find all uses of (including assignments to) a [`Local`].
+///
+/// Uses `BTreeSet` so output is deterministic.
+pub(super) fn find<'tcx>(body: &Body<'tcx>, local: Local) -> BTreeSet<Location> {
+    let mut visitor = AllLocalUsesVisitor { for_local: local, uses: BTreeSet::default() };
+    visitor.visit_body(body);
+    visitor.uses
+}
+
+struct AllLocalUsesVisitor {
+    for_local: Local,
+    uses: BTreeSet<Location>,
+}
+
+impl<'tcx> Visitor<'tcx> for AllLocalUsesVisitor {
+    fn visit_local(&mut self, local: &Local, _context: PlaceContext, location: Location) {
+        if *local == self.for_local {
+            self.uses.insert(location);
+        }
+    }
+}

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -19,6 +19,7 @@ use rustc_target::abi::VariantIdx;
 use super::borrow_set::BorrowData;
 use super::MirBorrowckCtxt;
 
+mod find_all_local_uses;
 mod find_use;
 mod outlives_suggestion;
 mod region_name;

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

@@ -384,6 +384,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         sub_r,
                         sup_origin,
                         sup_r,
+                        _,
                     ) => {
                         if sub_r.is_placeholder() {
                             self.report_placeholder_failure(sub_origin, sub_r, sup_r).emit();
@@ -464,7 +465,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         errors.sort_by_key(|u| match *u {
             RegionResolutionError::ConcreteFailure(ref sro, _, _) => sro.span(),
             RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
-            RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _) => rvo.span(),
+            RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
             RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
         });
         errors

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/mod.rs

@@ -67,7 +67,7 @@ impl<'cx, 'tcx> NiceRegionError<'cx, 'tcx> {
     pub fn regions(&self) -> Option<(Span, ty::Region<'tcx>, ty::Region<'tcx>)> {
         match (&self.error, self.regions) {
             (Some(ConcreteFailure(origin, sub, sup)), None) => Some((origin.span(), sub, sup)),
-            (Some(SubSupConflict(_, _, origin, sub, _, sup)), None) => {
+            (Some(SubSupConflict(_, _, origin, sub, _, sup, _)), None) => {
                 Some((origin.span(), sub, sup))
             }
             (None, Some((span, sub, sup))) => Some((span, sub, sup)),

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/placeholder_error.rs

@@ -34,6 +34,7 @@ impl NiceRegionError<'me, 'tcx> {
                 sub_placeholder @ ty::RePlaceholder(_),
                 _,
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -49,6 +50,7 @@ impl NiceRegionError<'me, 'tcx> {
                 sub_placeholder @ ty::RePlaceholder(_),
                 _,
                 _,
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -64,6 +66,7 @@ impl NiceRegionError<'me, 'tcx> {
                 _,
                 _,
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,
@@ -79,6 +82,7 @@ impl NiceRegionError<'me, 'tcx> {
                 _,
                 SubregionOrigin::Subtype(box TypeTrace { cause, values }),
                 sup_placeholder @ ty::RePlaceholder(_),
+                _,
             )) => self.try_report_trait_placeholder_mismatch(
                 Some(self.tcx().mk_region(ty::ReVar(*vid))),
                 cause,

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -10,7 +10,8 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{walk_ty, ErasedMap, NestedVisitorMap, Visitor};
 use rustc_hir::{self as hir, GenericBound, Item, ItemKind, Lifetime, LifetimeName, Node, TyKind};
 use rustc_middle::ty::{
-    self, AssocItemContainer, RegionKind, Ty, TyCtxt, TypeFoldable, TypeVisitor,
+    self, AssocItemContainer, RegionKind, StaticLifetimeVisitor, Ty, TyCtxt, TypeFoldable,
+    TypeVisitor,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::{MultiSpan, Span};
@@ -23,16 +24,17 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     pub(super) fn try_report_static_impl_trait(&self) -> Option<ErrorReported> {
         debug!("try_report_static_impl_trait(error={:?})", self.error);
         let tcx = self.tcx();
-        let (var_origin, sub_origin, sub_r, sup_origin, sup_r) = match self.error.as_ref()? {
+        let (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans) = match self.error.as_ref()? {
             RegionResolutionError::SubSupConflict(
                 _,
                 var_origin,
                 sub_origin,
                 sub_r,
                 sup_origin,
                 sup_r,
+                spans,
             ) if **sub_r == RegionKind::ReStatic => {
-                (var_origin, sub_origin, sub_r, sup_origin, sup_r)
+                (var_origin, sub_origin, sub_r, sup_origin, sup_r, spans)
             }
             RegionResolutionError::ConcreteFailure(
                 SubregionOrigin::Subtype(box TypeTrace { cause, .. }),
@@ -74,7 +76,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
                     err.span_label(
                         cause.span,
                         &format!(
-                            "...is captured and required to live as long as `'static` here \
+                            "...is used and required to live as long as `'static` here \
                              because of an implicit lifetime bound on the {}",
                             match ctxt.assoc_item.container {
                                 AssocItemContainer::TraitContainer(id) =>
@@ -123,56 +125,101 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             param_name,
             lifetime,
         );
-        err.span_label(param.param_ty_span, &format!("this data with {}...", lifetime));
-        debug!("try_report_static_impl_trait: param_info={:?}", param);
 
-        // We try to make the output have fewer overlapping spans if possible.
-        if (sp == sup_origin.span() || !return_sp.overlaps(sup_origin.span()))
-            && sup_origin.span() != return_sp
-        {
-            // FIXME: account for `async fn` like in `async-await/issues/issue-62097.rs`
-
-            // Customize the spans and labels depending on their relative order so
-            // that split sentences flow correctly.
-            if sup_origin.span().overlaps(return_sp) && sp == sup_origin.span() {
-                // Avoid the following:
-                //
-                // error: cannot infer an appropriate lifetime
-                //   --> $DIR/must_outlive_least_region_or_bound.rs:18:50
-                //    |
-                // LL | fn foo(x: &i32) -> Box<dyn Debug> { Box::new(x) }
-                //    |           ----                      ---------^-
+        let (mention_influencer, influencer_point) =
+            if sup_origin.span().overlaps(param.param_ty_span) {
+                // Account for `async fn` like in `async-await/issues/issue-62097.rs`.
+                // The desugaring of `async `fn`s causes `sup_origin` and `param` to point at the same
+                // place (but with different `ctxt`, hence `overlaps` instead of `==` above).
                 //
-                // and instead show:
+                // This avoids the following:
                 //
-                // error: cannot infer an appropriate lifetime
-                //   --> $DIR/must_outlive_least_region_or_bound.rs:18:50
-                //    |
-                // LL | fn foo(x: &i32) -> Box<dyn Debug> { Box::new(x) }
-                //    |           ----                               ^
-                err.span_label(
-                    sup_origin.span(),
-                    "...is captured here, requiring it to live as long as `'static`",
-                );
+                // LL |     pub async fn run_dummy_fn(&self) {
+                //    |                               ^^^^^
+                //    |                               |
+                //    |                               this data with an anonymous lifetime `'_`...
+                //    |                               ...is captured here...
+                (false, sup_origin.span())
             } else {
-                err.span_label(sup_origin.span(), "...is captured here...");
-                if return_sp < sup_origin.span() {
-                    err.span_note(
-                        return_sp,
-                        "...and is required to live as long as `'static` here",
+                (!sup_origin.span().overlaps(return_sp), param.param_ty_span)
+            };
+        err.span_label(influencer_point, &format!("this data with {}...", lifetime));
+
+        debug!("try_report_static_impl_trait: param_info={:?}", param);
+
+        let mut spans = spans.clone();
+
+        if mention_influencer {
+            spans.push(sup_origin.span());
+        }
+        // We dedup the spans *ignoring* expansion context.
+        spans.sort();
+        spans.dedup_by_key(|span| (span.lo(), span.hi()));
+
+        // We try to make the output have fewer overlapping spans if possible.
+        let require_msg = if spans.is_empty() {
+            "...is used and required to live as long as `'static` here"
+        } else {
+            "...and is required to live as long as `'static` here"
+        };
+        let require_span =
+            if sup_origin.span().overlaps(return_sp) { sup_origin.span() } else { return_sp };
+
+        for span in &spans {
+            err.span_label(*span, "...is used here...");
+        }
+
+        if spans.iter().any(|sp| sp.overlaps(return_sp) || *sp > return_sp) {
+            // If any of the "captured here" labels appears on the same line or after
+            // `require_span`, we put it on a note to ensure the text flows by appearing
+            // always at the end.
+            err.span_note(require_span, require_msg);
+        } else {
+            // We don't need a note, it's already at the end, it can be shown as a `span_label`.
+            err.span_label(require_span, require_msg);
+        }
+
+        if let SubregionOrigin::RelateParamBound(_, _, Some(bound)) = sub_origin {
+            err.span_note(*bound, "`'static` lifetime requirement introduced by this bound");
+        }
+        if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = sub_origin {
+            if let ObligationCauseCode::ReturnValue(hir_id)
+            | ObligationCauseCode::BlockTailExpression(hir_id) = &cause.code
+            {
+                let parent_id = tcx.hir().get_parent_item(*hir_id);
+                if let Some(fn_decl) = tcx.hir().fn_decl_by_hir_id(parent_id) {
+                    let mut span: MultiSpan = fn_decl.output.span().into();
+                    let mut add_label = true;
+                    if let hir::FnRetTy::Return(ty) = fn_decl.output {
+                        let mut v = StaticLifetimeVisitor(vec![], tcx.hir());
+                        v.visit_ty(ty);
+                        if !v.0.is_empty() {
+                            span = v.0.clone().into();
+                            for sp in v.0 {
+                                span.push_span_label(
+                                    sp,
+                                    "`'static` requirement introduced here".to_string(),
+                                );
+                            }
+                            add_label = false;
+                        }
+                    }
+                    if add_label {
+                        span.push_span_label(
+                            fn_decl.output.span(),
+                            "requirement introduced by this return type".to_string(),
+                        );
+                    }
+                    span.push_span_label(
+                        cause.span,
+                        "because of this returned expression".to_string(),
                     );
-                } else {
-                    err.span_label(
-                        return_sp,
-                        "...and is required to live as long as `'static` here",
+                    err.span_note(
+                        span,
+                        "`'static` lifetime requirement introduced by the return type",
                     );
                 }
             }
-        } else {
-            err.span_label(
-                return_sp,
-                "...is captured and required to live as long as `'static` here",
-            );
         }
 
         let fn_returns = tcx.return_type_impl_or_dyn_traits(anon_reg_sup.def_id);