Auto merge of #137124 - matthiaskrgr:rollup-0yymflu, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #125087 (Optimize `Seek::stream_len` impl for `File`)
 - #136986 (Apply unsafe_op_in_unsafe_fn to the standard library)
 - #137012 (add docs and ut for bootstrap util cc-detect)
 - #137072 (Load all builtin targets at once instead of one by one in check-cfg)
 - #137102 (Rework `name_regions` to not rely on reverse scc graph for non-member-constrain usages)
 - #137112 (Don't project into `NonNull` when dropping a `Box`)
 - #137114 (Add an example for `std::error::Error`)
 - #137117 (Fix test that relies on error language)
 - #137119 (fix broken `x {doc, build} core`)

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

Author: bors

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -14,7 +14,10 @@ use rustc_infer::infer::{NllRegionVariableOrigin, RelateParamBound};
 use rustc_middle::bug;
 use rustc_middle::hir::place::PlaceBase;
 use rustc_middle::mir::{AnnotationSource, ConstraintCategory, ReturnConstraint};
-use rustc_middle::ty::{self, GenericArgs, Region, RegionVid, Ty, TyCtxt, TypeVisitor};
+use rustc_middle::ty::fold::fold_regions;
+use rustc_middle::ty::{
+    self, GenericArgs, Region, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitor,
+};
 use rustc_span::{Ident, Span, kw};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::error_reporting::infer::nice_region_error::{
@@ -183,6 +186,17 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }
     }
 
+    /// Map the regions in the type to named regions, where possible.
+    fn name_regions<T>(&self, tcx: TyCtxt<'tcx>, ty: T) -> T
+    where
+        T: TypeFoldable<TyCtxt<'tcx>>,
+    {
+        fold_regions(tcx, ty, |region, _| match *region {
+            ty::ReVar(vid) => self.to_error_region(vid).unwrap_or(region),
+            _ => region,
+        })
+    }
+
     /// Returns `true` if a closure is inferred to be an `FnMut` closure.
     fn is_closure_fn_mut(&self, fr: RegionVid) -> bool {
         if let Some(ty::ReLateParam(late_param)) = self.to_error_region(fr).as_deref()
@@ -314,7 +328,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     let type_test_span = type_test.span;
 
                     if let Some(lower_bound_region) = lower_bound_region {
-                        let generic_ty = self.regioncx.name_regions(
+                        let generic_ty = self.name_regions(
                             self.infcx.tcx,
                             type_test.generic_kind.to_ty(self.infcx.tcx),
                         );
@@ -323,7 +337,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                             self.body.source.def_id().expect_local(),
                             type_test_span,
                             Some(origin),
-                            self.regioncx.name_regions(self.infcx.tcx, type_test.generic_kind),
+                            self.name_regions(self.infcx.tcx, type_test.generic_kind),
                             lower_bound_region,
                         ));
                     } else {
@@ -354,9 +368,13 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 }
 
                 RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, key, member_region } => {
-                    let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty);
-                    let named_key = self.regioncx.name_regions(self.infcx.tcx, key);
-                    let named_region = self.regioncx.name_regions(self.infcx.tcx, 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(),

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -204,7 +204,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// that the regions produced are in fact equal to the named region they are
     /// replaced with. This is fine because this function is only to improve the
     /// region names in error messages.
-    pub(crate) fn name_regions<T>(&self, tcx: TyCtxt<'tcx>, ty: T) -> T
+    ///
+    /// This differs from `MirBorrowckCtxt::name_regions` since it is particularly
+    /// lax with mapping region vids that are *shorter* than a universal region to
+    /// that universal region. This is useful for member region constraints since
+    /// we want to suggest a universal region name to capture even if it's technically
+    /// not equal to the error region.
+    pub(crate) fn name_regions_for_member_constraint<T>(&self, tcx: TyCtxt<'tcx>, ty: T) -> T
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {