Member constraints already covered all of E0482 already, so that error never occurred anymore

Author: oli-obk

compiler/rustc_error_codes/src/error_codes/E0482.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A lifetime of a returned value does not outlive the function call.
 
 Erroneous code example:
 
-```compile_fail,E0482
+```compile_fail,E0700
 fn prefix<'a>(
     words: impl Iterator<Item = &'a str>
 ) -> impl Iterator<Item = String> { // error!
@@ -41,7 +43,7 @@ fn prefix(
 
 A similar lifetime problem might arise when returning closures:
 
-```compile_fail,E0482
+```compile_fail,E0700
 fn foo(
     x: &mut Vec<i32>
 ) -> impl FnMut(&mut Vec<i32>) -> &[i32] { // error!

compiler/rustc_infer/src/infer/error_reporting/note.rs

@@ -53,9 +53,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::RelateObjectBound(span) => {
                 label_or_note(span, "...so that it can be closed over into an object");
             }
-            infer::CallReturn(span) => {
-                label_or_note(span, "...so that return value is valid for the call");
-            }
             infer::DataBorrowed(ty, span) => {
                 label_or_note(
                     span,
@@ -281,23 +278,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 );
                 err
             }
-            infer::CallReturn(span) => {
-                let mut err = struct_span_err!(
-                    self.tcx.sess,
-                    span,
-                    E0482,
-                    "lifetime of return value does not outlive the function call"
-                );
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "the return value is only valid for ",
-                    sup,
-                    "",
-                    None,
-                );
-                err
-            }
             infer::DataBorrowed(ty, span) => {
                 let mut err = struct_span_err!(
                     self.tcx.sess,

compiler/rustc_infer/src/infer/mod.rs

@@ -417,9 +417,6 @@ pub enum SubregionOrigin<'tcx> {
     /// (&'a &'b T) where a >= b
     ReferenceOutlivesReferent(Ty<'tcx>, Span),
 
-    /// Region in return type of invoked fn must enclose call
-    CallReturn(Span),
-
     /// Comparing the signature and requirements of an impl method against
     /// the containing trait.
     CompareImplMethodObligation {
@@ -1803,7 +1800,6 @@ impl<'tcx> SubregionOrigin<'tcx> {
             ReborrowUpvar(a, _) => a,
             DataBorrowed(_, a) => a,
             ReferenceOutlivesReferent(_, a) => a,
-            CallReturn(a) => a,
             CompareImplMethodObligation { span, .. } => span,
             CompareImplTypeObligation { span, .. } => span,
         }

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -6,7 +6,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic;
 use rustc_infer::infer::opaque_types::OpaqueTypeDecl;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{self, InferCtxt, InferOk};
+use rustc_infer::infer::{InferCtxt, InferOk};
 use rustc_middle::ty::fold::{BottomUpFolder, TypeFoldable, TypeFolder, TypeVisitor};
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst};
 use rustc_middle::ty::{self, OpaqueTypeKey, Ty, TyCtxt};
@@ -295,51 +295,14 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             hir::OpaqueTyOrigin::TyAlias => 0,
         };
 
-        let span = tcx.def_span(def_id);
-
-        // Check if the `impl Trait` bounds include region bounds.
-        // For example, this would be true for:
-        //
-        //     fn foo<'a, 'b, 'c>() -> impl Trait<'c> + 'a + 'b
-        //
-        // but false for:
-        //
-        //     fn foo<'c>() -> impl Trait<'c>
-        //
-        // unless `Trait` was declared like:
-        //
-        //     trait Trait<'c>: 'c
-        //
-        // in which case it would be true.
-        //
-        // This is used during regionck to decide whether we need to
-        // impose any additional constraints to ensure that region
-        // variables in `concrete_ty` wind up being constrained to
-        // something from `substs` (or, at minimum, things that outlive
-        // the fn body). (Ultimately, writeback is responsible for this
-        // check.)
-        let bounds = tcx.explicit_item_bounds(def_id);
-        debug!("{:#?}", bounds);
-        let bounds = bounds.iter().map(|(bound, _)| bound.subst(tcx, opaque_type_key.substs));
-        debug!("{:#?}", bounds);
-        let opaque_type = tcx.mk_opaque(def_id, opaque_type_key.substs);
-
-        // (A) The regions that appear in the hidden type must be equal to
+        // The regions that appear in the hidden type must be equal to
         // one of the regions in scope for the opaque type.
         self.generate_member_constraint(
             concrete_ty,
             opaque_defn,
             opaque_type_key,
             first_own_region,
         );
-
-        // (B) We can also generate outlives bounds that must be enforced.
-        for required_region in required_region_bounds(tcx, opaque_type, bounds) {
-            concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
-                tcx,
-                op: |r| self.sub_regions(infer::CallReturn(span), required_region, r),
-            });
-        }
     }
 
     /// As a fallback, we sometimes generate an "in constraint". For