Auto merge of #91865 - matthiaskrgr:rollup-rai9ecq, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #91699 (Add `-webkit-appearance: none` to search input)
 - #91846 (rustdoc: Reduce number of arguments for `run_test` a bit)
 - #91847 (Fix FIXME for `generic_arg_infer` in `create_substs_for_ast_path`)
 - #91849 (GATs outlives lint: Try to prove bounds)
 - #91855 (Stabilize const_cstr_unchecked)

Failed merges:

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

5 files changed, 81 insertions, 66 deletions

diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 62c17e6a10f..1dfaae7a150 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -6,7 +6,6 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
-#![feature(const_cstr_unchecked)]
 #![feature(crate_visibility_modifier)]
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]
diff --git a/compiler/rustc_infer/src/infer/free_regions.rs b/compiler/rustc_infer/src/infer/free_regions.rs
index 4814b65e320..e93cdf79421 100644
--- a/compiler/rustc_infer/src/infer/free_regions.rs
+++ b/compiler/rustc_infer/src/infer/free_regions.rs
@@ -11,7 +11,7 @@ use rustc_middle::ty::{self, Lift, Region, TyCtxt};
 ///
 /// This stuff is a bit convoluted and should be refactored, but as we
 /// transition to NLL, it'll all go away anyhow.
-pub struct RegionRelations<'a, 'tcx> {
+pub(crate) struct RegionRelations<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
 
     /// The context used for debug messages
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index 85ee6d2cdc2..a5ec84a4f14 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -28,7 +28,7 @@ use std::fmt;
 /// assuming such values can be found. It returns the final values of
 /// all the variables as well as a set of errors that must be reported.
 #[instrument(level = "debug", skip(region_rels, var_infos, data))]
-pub fn resolve<'tcx>(
+pub(crate) fn resolve<'tcx>(
     region_rels: &RegionRelations<'_, 'tcx>,
     var_infos: VarInfos,
     data: RegionConstraintData<'tcx>,
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index 752183365d6..aad8dd2119f 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -414,34 +414,40 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 arg: &GenericArg<'_>,
             ) -> subst::GenericArg<'tcx> {
                 let tcx = self.astconv.tcx();
+
+                let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
+                    if has_default {
+                        tcx.check_optional_stability(
+                            param.def_id,
+                            Some(arg.id()),
+                            arg.span(),
+                            None,
+                            |_, _| {
+                                // Default generic parameters may not be marked
+                                // with stability attributes, i.e. when the
+                                // default parameter was defined at the same time
+                                // as the rest of the type. As such, we ignore missing
+                                // stability attributes.
+                            },
+                        )
+                    }
+                    if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
+                        self.inferred_params.push(ty.span);
+                        tcx.ty_error().into()
+                    } else {
+                        self.astconv.ast_ty_to_ty(ty).into()
+                    }
+                };
+
                 match (&param.kind, arg) {
                     (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
                         self.astconv.ast_region_to_region(lt, Some(param)).into()
                     }
                     (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
-                        if has_default {
-                            tcx.check_optional_stability(
-                                param.def_id,
-                                Some(arg.id()),
-                                arg.span(),
-                                None,
-                                |_, _| {
-                                    // Default generic parameters may not be marked
-                                    // with stability attributes, i.e. when the
-                                    // default parameter was defined at the same time
-                                    // as the rest of the type. As such, we ignore missing
-                                    // stability attributes.
-                                },
-                            )
-                        }
-                        if let (hir::TyKind::Infer, false) =
-                            (&ty.kind, self.astconv.allow_ty_infer())
-                        {
-                            self.inferred_params.push(ty.span);
-                            tcx.ty_error().into()
-                        } else {
-                            self.astconv.ast_ty_to_ty(ty).into()
-                        }
+                        handle_ty_args(has_default, ty)
+                    }
+                    (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
+                        handle_ty_args(has_default, &inf.to_ty())
                     }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
                         ty::Const::from_opt_const_arg_anon_const(
@@ -453,41 +459,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         )
                         .into()
                     }
-                    (&GenericParamDefKind::Const { has_default }, hir::GenericArg::Infer(inf)) => {
-                        if has_default {
-                            tcx.const_param_default(param.def_id).into()
-                        } else if self.astconv.allow_ty_infer() {
-                            // FIXME(const_generics): Actually infer parameter here?
-                            todo!()
-                        } else {
-                            self.inferred_params.push(inf.span);
-                            tcx.ty_error().into()
-                        }
-                    }
-                    (
-                        &GenericParamDefKind::Type { has_default, .. },
-                        hir::GenericArg::Infer(inf),
-                    ) => {
-                        if has_default {
-                            tcx.check_optional_stability(
-                                param.def_id,
-                                Some(arg.id()),
-                                arg.span(),
-                                None,
-                                |_, _| {
-                                    // Default generic parameters may not be marked
-                                    // with stability attributes, i.e. when the
-                                    // default parameter was defined at the same time
-                                    // as the rest of the type. As such, we ignore missing
-                                    // stability attributes.
-                                },
-                            );
-                        }
+                    (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
+                        let ty = tcx.at(self.span).type_of(param.def_id);
                         if self.astconv.allow_ty_infer() {
-                            self.astconv.ast_ty_to_ty(&inf.to_ty()).into()
+                            self.astconv.ct_infer(ty, Some(param), inf.span).into()
                         } else {
                             self.inferred_params.push(inf.span);
-                            tcx.ty_error().into()
+                            tcx.const_error(ty).into()
                         }
                     }
                     _ => unreachable!(),
diff --git a/compiler/rustc_typeck/src/check/wfcheck.rs b/compiler/rustc_typeck/src/check/wfcheck.rs
index 3fd3284d8b1..1404bc27167 100644
--- a/compiler/rustc_typeck/src/check/wfcheck.rs
+++ b/compiler/rustc_typeck/src/check/wfcheck.rs
@@ -426,22 +426,48 @@ fn check_gat_where_clauses(
         }
     }
 
-    // If there are any missing clauses, emit an error
-    let mut clauses = clauses.unwrap_or_default();
+    // If there are any clauses that aren't provable, emit an error
+    let clauses = clauses.unwrap_or_default();
     debug!(?clauses);
     if !clauses.is_empty() {
-        let written_predicates: ty::GenericPredicates<'_> =
-            tcx.explicit_predicates_of(trait_item.def_id);
+        let param_env = tcx.param_env(trait_item.def_id);
+
         let mut clauses: Vec<_> = clauses
-            .drain_filter(|clause| !written_predicates.predicates.iter().any(|p| &p.0 == clause))
+            .into_iter()
+            .filter(|clause| match clause.kind().skip_binder() {
+                ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
+                    !region_known_to_outlive(
+                        tcx,
+                        trait_item.hir_id(),
+                        param_env,
+                        &FxHashSet::default(),
+                        a,
+                        b,
+                    )
+                }
+                ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
+                    !ty_known_to_outlive(
+                        tcx,
+                        trait_item.hir_id(),
+                        param_env,
+                        &FxHashSet::default(),
+                        a,
+                        b,
+                    )
+                }
+                _ => bug!("Unexpected PredicateKind"),
+            })
             .map(|clause| format!("{}", clause))
             .collect();
+
         // We sort so that order is predictable
         clauses.sort();
+
         if !clauses.is_empty() {
+            let plural = if clauses.len() > 1 { "s" } else { "" };
             let mut err = tcx.sess.struct_span_err(
                 trait_item.span,
-                &format!("Missing required bounds on {}", trait_item.ident),
+                &format!("missing required bound{} on `{}`", plural, trait_item.ident),
             );
 
             let suggestion = format!(
@@ -455,11 +481,22 @@ fn check_gat_where_clauses(
             );
             err.span_suggestion(
                 trait_item.generics.where_clause.tail_span_for_suggestion(),
-                "add the required where clauses",
+                &format!("add the required where clause{}", plural),
                 suggestion,
                 Applicability::MachineApplicable,
             );
 
+            let bound = if clauses.len() > 1 { "these bounds are" } else { "this bound is" };
+            err.note(&format!(
+                "{} currently required to ensure that impls have maximum flexibility",
+                bound
+            ));
+            err.note(
+                "we are soliciting feedback, see issue #87479 \
+                 <https://github.com/rust-lang/rust/issues/87479> \
+                 for more information",
+            );
+
             err.emit()
         }
     }
@@ -541,7 +578,8 @@ fn region_known_to_outlive<'tcx>(
         });
 
         use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
-        (&infcx).push_sub_region_constraint(origin, region_a, region_b);
+        // `region_a: region_b` -> `region_b <= region_a`
+        (&infcx).push_sub_region_constraint(origin, region_b, region_a);
 
         let errors = infcx.resolve_regions(
             id.expect_owner().to_def_id(),