Rollup merge of #114301 - compiler-errors:dont-error-on-missing-region-outlives, r=spastorino

Don't check unnecessarily that impl trait is RPIT

We have this random `return_type_impl_trait` function to detect if a function returns an RPIT which is used in outlives suggestions, but removing it doesn't actually change any diagnostics. Let's just remove it.

Also, suppress a spurious outlives error from a ReError.

Fixes #114274

Author: matthiaskrgr

Diff for: compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -555,8 +555,8 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     for (region_a, region_a_idx) in &regions {
         // Ignore `'static` lifetimes for the purpose of this lint: it's
         // because we know it outlives everything and so doesn't give meaningful
-        // clues
-        if let ty::ReStatic = **region_a {
+        // clues. Also ignore `ReError`, to avoid knock-down errors.
+        if let ty::ReStatic | ty::ReError(_) = **region_a {
             continue;
         }
         // For each region argument (e.g., `'a` in our example), check for a
@@ -599,8 +599,9 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
         // on the GAT itself.
         for (region_b, region_b_idx) in &regions {
             // Again, skip `'static` because it outlives everything. Also, we trivially
-            // know that a region outlives itself.
-            if ty::ReStatic == **region_b || region_a == region_b {
+            // know that a region outlives itself. Also ignore `ReError`, to avoid
+            // knock-down errors.
+            if matches!(**region_b, ty::ReStatic | ty::ReError(_)) || region_a == region_b {
                 continue;
             }
             if region_known_to_outlive(

Diff for: compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -2567,15 +2567,13 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     None,
                 );
                 if let Some(infer::RelateParamBound(_, t, _)) = origin {
-                    let return_impl_trait =
-                        self.tcx.return_type_impl_trait(generic_param_scope).is_some();
                     let t = self.resolve_vars_if_possible(t);
                     match t.kind() {
                         // We've got:
                         // fn get_later<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
                         // suggest:
                         // fn get_later<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
-                        ty::Closure(..) | ty::Alias(ty::Opaque, ..) if return_impl_trait => {
+                        ty::Closure(..) | ty::Alias(ty::Opaque, ..) => {
                             new_binding_suggestion(&mut err, type_param_span);
                         }
                         _ => {

Diff for: compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -942,6 +942,10 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         generic_ty: Ty<'tcx>,
         min: ty::Region<'tcx>,
     ) -> bool {
+        if let ty::ReError(_) = *min {
+            return true;
+        }
+
         match bound {
             VerifyBound::IfEq(verify_if_eq_b) => {
                 let verify_if_eq_b = var_values.normalize(self.region_rels.tcx, *verify_if_eq_b);

Diff for: compiler/rustc_middle/src/ty/context.rs

@@ -50,9 +50,7 @@ use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::definitions::Definitions;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
-use rustc_hir::{
-    Constness, ExprKind, HirId, ImplItemKind, ItemKind, Node, TraitCandidate, TraitItemKind,
-};
+use rustc_hir::{Constness, HirId, Node, TraitCandidate};
 use rustc_index::IndexVec;
 use rustc_macros::HashStable;
 use rustc_query_system::dep_graph::DepNodeIndex;
@@ -1077,31 +1075,6 @@ impl<'tcx> TyCtxt<'tcx> {
         return None;
     }
 
-    pub fn return_type_impl_trait(self, scope_def_id: LocalDefId) -> Option<(Ty<'tcx>, Span)> {
-        // `type_of()` will fail on these (#55796, #86483), so only allow `fn`s or closures.
-        match self.hir().get_by_def_id(scope_def_id) {
-            Node::Item(&hir::Item { kind: ItemKind::Fn(..), .. }) => {}
-            Node::TraitItem(&hir::TraitItem { kind: TraitItemKind::Fn(..), .. }) => {}
-            Node::ImplItem(&hir::ImplItem { kind: ImplItemKind::Fn(..), .. }) => {}
-            Node::Expr(&hir::Expr { kind: ExprKind::Closure { .. }, .. }) => {}
-            _ => return None,
-        }
-
-        let ret_ty = self.type_of(scope_def_id).instantiate_identity();
-        match ret_ty.kind() {
-            ty::FnDef(_, _) => {
-                let sig = ret_ty.fn_sig(self);
-                let output = self.erase_late_bound_regions(sig.output());
-                output.is_impl_trait().then(|| {
-                    let hir_id = self.hir().local_def_id_to_hir_id(scope_def_id);
-                    let fn_decl = self.hir().fn_decl_by_hir_id(hir_id).unwrap();
-                    (output, fn_decl.output.span())
-                })
-            }
-            _ => None,
-        }
-    }
-
     /// Checks if the bound region is in Impl Item.
     pub fn is_bound_region_in_impl_item(self, suitable_region_binding_scope: LocalDefId) -> bool {
         let container_id = self.parent(suitable_region_binding_scope.to_def_id());

Diff for: tests/ui/impl-trait/in-trait/missing-lt-outlives-in-rpitit-114274.rs

@@ -0,0 +1,12 @@
+#![feature(return_position_impl_trait_in_trait)]
+
+trait Iterable {
+    type Item<'a>
+    where
+        Self: 'a;
+
+    fn iter(&self) -> impl Iterator<Item = Self::Item<'missing>>;
+    //~^ ERROR use of undeclared lifetime name `'missing`
+}
+
+fn main() {}

Diff for: tests/ui/impl-trait/in-trait/missing-lt-outlives-in-rpitit-114274.stderr

@@ -0,0 +1,23 @@
+error[E0261]: use of undeclared lifetime name `'missing`
+  --> $DIR/missing-lt-outlives-in-rpitit-114274.rs:8:55
+   |
+LL |     fn iter(&self) -> impl Iterator<Item = Self::Item<'missing>>;
+   |                                                       ^^^^^^^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'missing` lifetime
+   |
+LL |     fn iter(&self) -> impl for<'missing> Iterator<Item = Self::Item<'missing>>;
+   |                            +++++++++++++
+help: consider introducing lifetime `'missing` here
+   |
+LL |     fn iter<'missing>(&self) -> impl Iterator<Item = Self::Item<'missing>>;
+   |            ++++++++++
+help: consider introducing lifetime `'missing` here
+   |
+LL | trait Iterable<'missing> {
+   |               ++++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0261`.