cleanup: remove ExtraConstraintInfo

dianne · dianne · commit 7fea859150e1 · 2024-12-13T11:14:53.000-08:00
`ExtraConstraintInfo` was used only for a single subdiagnostic, so this moves the logic for that
to its own function and eliminates the indirection. In order to do so cleanly, this also changes
the arguments to `BorrowExplanation::add_explanation_to_diagnostic`, which happens to simplify its
call sites.
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -1517,15 +1517,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         });
 
         self.explain_why_borrow_contains_point(location, borrow, None)
-            .add_explanation_to_diagnostic(
-                self.infcx.tcx,
-                self.body,
-                &self.local_names,
-                &mut err,
-                "",
-                Some(borrow_span),
-                None,
-            );
+            .add_explanation_to_diagnostic(&self, &mut err, "", Some(borrow_span), None);
         self.suggest_copy_for_type_in_cloned_ref(&mut err, place);
         let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
         if let Some(expr) = self.find_expr(borrow_span) {
@@ -1592,15 +1584,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         });
 
         self.explain_why_borrow_contains_point(location, borrow, None)
-            .add_explanation_to_diagnostic(
-                self.infcx.tcx,
-                self.body,
-                &self.local_names,
-                &mut err,
-                "",
-                None,
-                None,
-            );
+            .add_explanation_to_diagnostic(&self, &mut err, "", None, None);
         err
     }
 
@@ -1887,9 +1871,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }
 
         explanation.add_explanation_to_diagnostic(
-            self.infcx.tcx,
-            self.body,
-            &self.local_names,
+            &self,
             &mut err,
             first_borrow_desc,
             None,
@@ -3047,15 +3029,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
             if let BorrowExplanation::MustBeValidFor { .. } = explanation {
             } else {
-                explanation.add_explanation_to_diagnostic(
-                    self.infcx.tcx,
-                    self.body,
-                    &self.local_names,
-                    &mut err,
-                    "",
-                    None,
-                    None,
-                );
+                explanation.add_explanation_to_diagnostic(&self, &mut err, "", None, None);
             }
         } else {
             err.span_label(borrow_span, "borrowed value does not live long enough");
@@ -3068,15 +3042,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 }
             });
 
-            explanation.add_explanation_to_diagnostic(
-                self.infcx.tcx,
-                self.body,
-                &self.local_names,
-                &mut err,
-                "",
-                Some(borrow_span),
-                None,
-            );
+            explanation.add_explanation_to_diagnostic(&self, &mut err, "", Some(borrow_span), None);
         }
 
         err
@@ -3129,15 +3095,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             _ => {}
         }
 
-        explanation.add_explanation_to_diagnostic(
-            self.infcx.tcx,
-            self.body,
-            &self.local_names,
-            &mut err,
-            "",
-            None,
-            None,
-        );
+        explanation.add_explanation_to_diagnostic(&self, &mut err, "", None, None);
 
         self.buffer_error(err);
     }
@@ -3310,15 +3268,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
             _ => {}
         }
-        explanation.add_explanation_to_diagnostic(
-            self.infcx.tcx,
-            self.body,
-            &self.local_names,
-            &mut err,
-            "",
-            None,
-            None,
-        );
+        explanation.add_explanation_to_diagnostic(&self, &mut err, "", None, None);
 
         borrow_spans.args_subdiag(&mut err, |args_span| {
             crate::session_diagnostics::CaptureArgLabel::Capture {
@@ -3809,15 +3759,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
         });
 
-        self.explain_why_borrow_contains_point(location, loan, None).add_explanation_to_diagnostic(
-            self.infcx.tcx,
-            self.body,
-            &self.local_names,
-            &mut err,
-            "",
-            None,
-            None,
-        );
+        self.explain_why_borrow_contains_point(location, loan, None)
+            .add_explanation_to_diagnostic(&self, &mut err, "", None, None);
 
         self.explain_deref_coercion(loan, &mut err);
 
diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
@@ -8,7 +8,6 @@ use std::assert_matches::assert_matches;
 use rustc_errors::{Applicability, Diag};
 use rustc_hir as hir;
 use rustc_hir::intravisit::Visitor;
-use rustc_index::IndexSlice;
 use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
 use rustc_middle::mir::{
@@ -17,15 +16,16 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
-use rustc_span::symbol::{Symbol, kw};
+use rustc_span::symbol::kw;
 use rustc_span::{DesugaringKind, Span, sym};
 use rustc_trait_selection::error_reporting::traits::FindExprBySpan;
 use tracing::{debug, instrument};
 
 use super::{RegionName, UseSpans, find_use};
 use crate::borrow_set::BorrowData;
+use crate::constraints::OutlivesConstraint;
 use crate::nll::ConstraintDescription;
-use crate::region_infer::{BlameConstraint, Cause, ExtraConstraintInfo};
+use crate::region_infer::{BlameConstraint, Cause};
 use crate::{MirBorrowckCtxt, WriteKind};
 
 #[derive(Debug)]
@@ -43,7 +43,7 @@ pub(crate) enum BorrowExplanation<'tcx> {
         span: Span,
         region_name: RegionName,
         opt_place_desc: Option<String>,
-        extra_info: Vec<ExtraConstraintInfo>,
+        path: Vec<OutlivesConstraint<'tcx>>,
     },
     Unexplained,
 }
@@ -63,14 +63,16 @@ impl<'tcx> BorrowExplanation<'tcx> {
     }
     pub(crate) fn add_explanation_to_diagnostic(
         &self,
-        tcx: TyCtxt<'tcx>,
-        body: &Body<'tcx>,
-        local_names: &IndexSlice<Local, Option<Symbol>>,
+        cx: &MirBorrowckCtxt<'_, '_, 'tcx>,
         err: &mut Diag<'_>,
         borrow_desc: &str,
         borrow_span: Option<Span>,
         multiple_borrow_span: Option<(Span, Span)>,
     ) {
+        let tcx = cx.infcx.tcx;
+        let body = cx.body;
+        let local_names = &cx.local_names;
+
         if let Some(span) = borrow_span {
             let def_id = body.source.def_id();
             if let Some(node) = tcx.hir().get_if_local(def_id)
@@ -306,7 +308,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                 ref region_name,
                 ref opt_place_desc,
                 from_closure: _,
-                ref extra_info,
+                ref path,
             } => {
                 region_name.highlight_region_name(err);
 
@@ -328,13 +330,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     );
                 };
 
-                for extra in extra_info {
-                    match extra {
-                        ExtraConstraintInfo::PlaceholderFromPredicate(span) => {
-                            err.span_note(*span, "due to current limitations in the borrow checker, this implies a `'static` lifetime");
-                        }
-                    }
-                }
+                cx.add_placeholder_from_predicate_note(err, &path);
 
                 if let ConstraintCategory::Cast {
                     is_implicit_coercion: true,
@@ -487,8 +483,9 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         &self,
         borrow_region: RegionVid,
         outlived_region: RegionVid,
-    ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>, Vec<ExtraConstraintInfo>) {
-        let (blame_constraint, extra_info) = self.regioncx.best_blame_constraint(
+    ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>, Vec<OutlivesConstraint<'tcx>>)
+    {
+        let (blame_constraint, path) = self.regioncx.best_blame_constraint(
             borrow_region,
             NllRegionVariableOrigin::FreeRegion,
             |r| self.regioncx.provides_universal_region(r, borrow_region, outlived_region),
@@ -497,7 +494,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
 
         let outlived_fr_name = self.give_region_a_name(outlived_region);
 
-        (category, from_closure, cause.span, outlived_fr_name, extra_info)
+        (category, from_closure, cause.span, outlived_fr_name, path)
     }
 
     /// Returns structured explanation for *why* the borrow contains the
@@ -596,7 +593,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
 
             None => {
                 if let Some(region) = self.to_error_region_vid(borrow_region_vid) {
-                    let (category, from_closure, span, region_name, extra_info) =
+                    let (category, from_closure, span, region_name, path) =
                         self.free_region_constraint_info(borrow_region_vid, region);
                     if let Some(region_name) = region_name {
                         let opt_place_desc = self.describe_place(borrow.borrowed_place.as_ref());
@@ -606,7 +603,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
                             span,
                             region_name,
                             opt_place_desc,
-                            extra_info,
+                            path,
                         }
                     } else {
                         debug!("Could not generate a region name");
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -5,14 +5,16 @@ use rustc_errors::{Applicability, Diag, MultiSpan};
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::{self as hir, CoroutineKind, LangItem};
 use rustc_index::IndexSlice;
-use rustc_infer::infer::BoundRegionConversionTime;
+use rustc_infer::infer::{
+    BoundRegionConversionTime, NllRegionVariableOrigin, RegionVariableOrigin,
+};
 use rustc_infer::traits::SelectionError;
 use rustc_middle::bug;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
-    AggregateKind, CallSource, ConstOperand, FakeReadCause, Local, LocalInfo, LocalKind, Location,
-    Operand, Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator,
-    TerminatorKind,
+    AggregateKind, CallSource, ConstOperand, ConstraintCategory, FakeReadCause, Local, LocalInfo,
+    LocalKind, Location, Operand, Place, PlaceRef, ProjectionElem, Rvalue, Statement,
+    StatementKind, Terminator, TerminatorKind,
 };
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
@@ -31,6 +33,7 @@ use tracing::debug;
 
 use super::MirBorrowckCtxt;
 use super::borrow_set::BorrowData;
+use crate::constraints::OutlivesConstraint;
 use crate::fluent_generated as fluent;
 use crate::session_diagnostics::{
     CaptureArgLabel, CaptureReasonLabel, CaptureReasonNote, CaptureReasonSuggest, CaptureVarCause,
@@ -497,6 +500,31 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         region.print(&mut printer).unwrap();
         printer.into_buffer()
     }
+
+    /// Add a note to region errors and borrow explanations when higher-ranked regions in predicates
+    /// implicitly introduce an "outlives `'static`" constraint.
+    fn add_placeholder_from_predicate_note(
+        &self,
+        err: &mut Diag<'_>,
+        path: &[OutlivesConstraint<'tcx>],
+    ) {
+        let predicate_span = path.iter().find_map(|constraint| {
+            let outlived = constraint.sub;
+            if let Some(origin) = self.regioncx.var_infos.get(outlived)
+                && let RegionVariableOrigin::Nll(NllRegionVariableOrigin::Placeholder(_)) =
+                    origin.origin
+                && let ConstraintCategory::Predicate(span) = constraint.category
+            {
+                Some(span)
+            } else {
+                None
+            }
+        });
+
+        if let Some(span) = predicate_span {
+            err.span_note(span, "due to current limitations in the borrow checker, this implies a `'static` lifetime");
+        }
+    }
 }
 
 /// The span(s) associated to a use of a place.
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -30,7 +30,7 @@ use tracing::{debug, instrument, trace};
 use super::{OutlivesSuggestionBuilder, RegionName, RegionNameSource};
 use crate::nll::ConstraintDescription;
 use crate::region_infer::values::RegionElement;
-use crate::region_infer::{BlameConstraint, ExtraConstraintInfo, TypeTest};
+use crate::region_infer::{BlameConstraint, TypeTest};
 use crate::session_diagnostics::{
     FnMutError, FnMutReturnTypeErr, GenericDoesNotLiveLongEnough, LifetimeOutliveErr,
     LifetimeReturnCategoryErr, RequireStaticErr, VarHereDenote,
@@ -441,10 +441,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     ) {
         debug!("report_region_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr);
 
-        let (blame_constraint, extra_info) =
-            self.regioncx.best_blame_constraint(fr, fr_origin, |r| {
-                self.regioncx.provides_universal_region(r, fr, outlived_fr)
-            });
+        let (blame_constraint, path) = self.regioncx.best_blame_constraint(fr, fr_origin, |r| {
+            self.regioncx.provides_universal_region(r, fr, outlived_fr)
+        });
         let BlameConstraint { category, cause, variance_info, .. } = blame_constraint;
 
         debug!("report_region_error: category={:?} {:?} {:?}", category, cause, variance_info);
@@ -555,13 +554,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }
         }
 
-        for extra in extra_info {
-            match extra {
-                ExtraConstraintInfo::PlaceholderFromPredicate(span) => {
-                    diag.span_note(span, "due to current limitations in the borrow checker, this implies a `'static` lifetime");
-                }
-            }
-        }
+        self.add_placeholder_from_predicate_note(&mut diag, &path);
 
         self.buffer_error(diag);
     }
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
