Fix most of the cases of missing "implied 'static" warnings

Author: amandasystems

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -203,22 +203,36 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     fn suggest_static_lifetime_for_gat_from_hrtb(
         &self,
         diag: &mut Diag<'_>,
-        _lower_bound: RegionVid,
-    ) {
+        lower_bound: RegionVid,
+    ) -> Option<()> {
         let mut suggestions = vec![];
         let hir = self.infcx.tcx.hir();
 
         // find higher-ranked trait bounds bounded to the generic associated types
-        let hrtb_bounds = vec![];
-        /*
-        // FIXME: the best we can do is look at the representative, using something like:
         let scc = self.regioncx.constraint_sccs().scc(lower_bound);
-        let Some(representative) =
-            self.regioncx.constraint_sccs().annotation(scc).placeholder_representative()
-        else {
-            return;
-        };
-        */
+        let placeholder: ty::PlaceholderRegion = self.regioncx.placeholder_representative(scc)?;
+        let placeholder_id = placeholder.bound.kind.get_id()?.as_local()?;
+        let gat_hir_id = self.infcx.tcx.local_def_id_to_hir_id(placeholder_id);
+        let generics_impl =
+            self.infcx.tcx.parent_hir_node(self.infcx.tcx.parent_hir_id(gat_hir_id)).generics()?;
+
+        let mut hrtb_bounds = vec![];
+
+        for pred in generics_impl.predicates {
+            let BoundPredicate(WhereBoundPredicate { bound_generic_params, bounds, .. }) = pred
+            else {
+                continue;
+            };
+            if bound_generic_params
+                .iter()
+                .rfind(|bgp| self.infcx.tcx.local_def_id_to_hir_id(bgp.def_id) == gat_hir_id)
+                .is_some()
+            {
+                for bound in *bounds {
+                    hrtb_bounds.push(bound);
+                }
+            }
+        }
 
         hrtb_bounds.iter().for_each(|bound| {
             let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }, _) = bound else {
@@ -267,6 +281,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 Applicability::MaybeIncorrect,
             );
         }
+        Some(())
     }
 
     /// Produces nice borrowck error diagnostics for all the errors collected in `nll_errors`.

compiler/rustc_borrowck/src/nll.rs

@@ -119,13 +119,12 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     // base constraints generated by the type-check.
     let var_origins = infcx.get_region_var_origins();
     let MirTypeckRegionConstraints {
-        placeholder_indices: _,
-        placeholder_index_to_region: _,
         liveness_constraints,
         mut outlives_constraints,
         mut member_constraints,
         universe_causes,
         type_tests,
+        ..
     } = constraints;
 
     // If requested, emit legacy polonius facts.

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -18,7 +18,9 @@ use rustc_middle::mir::{
     TerminatorKind,
 };
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
-use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, UniverseIndex};
+use rustc_middle::ty::{
+    self, PlaceholderRegion, RegionVid, Ty, TyCtxt, TypeFoldable, UniverseIndex,
+};
 use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_span::Span;
 
@@ -2226,6 +2228,20 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     fn is_static(&self, r: RegionVid) -> bool {
         r == self.universal_regions.fr_static
     }
+
+    pub(crate) fn placeholder_representative(
+        &self,
+        scc: ConstraintSccIndex,
+    ) -> Option<PlaceholderRegion> {
+        if let Some(representative) =
+            self.constraint_sccs.annotation(scc).placeholder_representative()
+            && let NllRegionVariableOrigin::Placeholder(p) = self.definitions[representative].origin
+        {
+            Some(p)
+        } else {
+            None
+        }
+    }
 }
 
 impl<'tcx> RegionDefinition<'tcx> {

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -212,20 +212,26 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
                 // Special handling of higher-ranked regions.
                 if !self.scc_universe(scc).is_root() {
-                    if self
-                        .constraint_sccs
-                        .annotation(scc)
-                        .placeholder_representative()
-                        .is_some_and(|representative| representative == vid)
+                    let higher_ranked_region = if let Some(representative) =
+                        self.placeholder_representative(scc)
                     {
-                        if let NllRegionVariableOrigin::Placeholder(p) =
-                            self.definitions[vid].origin
-                        {
-                            return ty::Region::new_placeholder(tcx, p);
-                        }
-                    }
-                    debug!("Cannot get a nice name for higher-ranked region {vid:?} as {region:?}");
-                    return region;
+                        // FIXME: remove this assertion once the tests pass!
+                        assert!(
+                            self.constraint_sccs
+                                .annotation(scc)
+                                .placeholder_representative()
+                                .is_some_and(|representative| representative == vid)
+                        );
+
+                        ty::Region::new_placeholder(tcx, representative)
+                    } else {
+                        debug!(
+                            "Cannot get a nice name for higher-ranked region {vid:?} as {region:?}"
+                        );
+
+                        region
+                    };
+                    return higher_ranked_region;
                 }
 
                 // Find something that we can name

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -890,14 +890,14 @@ pub(crate) struct MirTypeckRegionConstraints<'tcx> {
     ///
     /// To keep everything in sync, do not insert this set
     /// directly. Instead, use the `placeholder_region` helper.
-    pub(crate) placeholder_indices: PlaceholderIndices,
+    placeholder_indices: PlaceholderIndices,
 
     /// Each time we add a placeholder to `placeholder_indices`, we
     /// also create a corresponding "representative" region vid for
     /// that wraps it. This vector tracks those. This way, when we
     /// convert the same `ty::RePlaceholder(p)` twice, we can map to
     /// the same underlying `RegionVid`.
-    pub(crate) placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
+    placeholder_index_to_region: IndexVec<PlaceholderIndex, ty::Region<'tcx>>,
 
     /// In general, the type-checker is not responsible for enforcing
     /// liveness constraints; this job falls to the region inferencer,