Auto merge of #80960 - Dylan-DPC:rollup-89tri8x, r=Dylan-DPC

Rollup of 10 pull requests

Successful merges:

 - #78901 (diagnostics: Note capturing closures can't be coerced to fns)
 - #79588 (Provide more information for HRTB lifetime errors involving closures)
 - #80232 (Remove redundant def_id lookups)
 - #80662 (Added support for i386-unknown-linux-gnu and i486-unknown-linux-gnu)
 - #80736 (use Once instead of Mutex to manage capture resolution)
 - #80796 (Update to LLVM 11.0.1)
 - #80859 (Fix --pretty=expanded with --remap-path-prefix)
 - #80922 (Revert "Auto merge of #76896 - spastorino:codegen-inline-fns2)
 - #80924 (Fix rustdoc --test-builder argument parsing)
 - #80935 (Rename `rustc_middle::lint::LevelSource` to `LevelAndSource`)

Failed merges:

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

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

@@ -98,7 +98,7 @@ pub(super) fn note_and_explain_region(
         // uh oh, hope no user ever sees THIS
         ty::ReEmpty(ui) => (format!("the empty lifetime in universe {:?}", ui), None),
 
-        ty::RePlaceholder(_) => ("any other region".to_string(), None),
+        ty::RePlaceholder(_) => return,
 
         // FIXME(#13998) RePlaceholder should probably print like
         // ReFree rather than dumping Debug output on the user.
@@ -1675,6 +1675,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         self.check_and_note_conflicting_crates(diag, terr);
         self.tcx.note_and_explain_type_err(diag, terr, cause, span, body_owner_def_id.to_def_id());
 
+        if let Some(ValuePairs::PolyTraitRefs(exp_found)) = values {
+            if let ty::Closure(def_id, _) = exp_found.expected.skip_binder().self_ty().kind() {
+                if let Some(def_id) = def_id.as_local() {
+                    let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+                    let span = self.tcx.hir().span(hir_id);
+                    diag.span_note(span, "this closure does not fulfill the lifetime requirements");
+                }
+            }
+        }
+
         // It reads better to have the error origin as the final
         // thing.
         self.note_error_origin(diag, cause, exp_found);

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

@@ -1,6 +1,7 @@
 use crate::infer::error_reporting::{note_and_explain_region, ObligationCauseExt};
 use crate::infer::{self, InferCtxt, SubregionOrigin};
 use rustc_errors::{struct_span_err, DiagnosticBuilder};
+use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{self, Region};
 
@@ -107,14 +108,37 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::Subtype(box trace) => {
                 let terr = TypeError::RegionsDoesNotOutlive(sup, sub);
                 let mut err = self.report_and_explain_type_error(trace, &terr);
-                note_and_explain_region(self.tcx, &mut err, "", sup, "...");
-                note_and_explain_region(
-                    self.tcx,
-                    &mut err,
-                    "...does not necessarily outlive ",
-                    sub,
-                    "",
-                );
+                match (sub, sup) {
+                    (ty::RePlaceholder(_), ty::RePlaceholder(_)) => {}
+                    (ty::RePlaceholder(_), _) => {
+                        note_and_explain_region(
+                            self.tcx,
+                            &mut err,
+                            "",
+                            sup,
+                            " doesn't meet the lifetime requirements",
+                        );
+                    }
+                    (_, ty::RePlaceholder(_)) => {
+                        note_and_explain_region(
+                            self.tcx,
+                            &mut err,
+                            "the required lifetime does not necessarily outlive ",
+                            sub,
+                            "",
+                        );
+                    }
+                    _ => {
+                        note_and_explain_region(self.tcx, &mut err, "", sup, "...");
+                        note_and_explain_region(
+                            self.tcx,
+                            &mut err,
+                            "...does not necessarily outlive ",
+                            sub,
+                            "",
+                        );
+                    }
+                }
                 err
             }
             infer::Reborrow(span) => {
@@ -286,13 +310,31 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         sup: Region<'tcx>,
     ) -> DiagnosticBuilder<'tcx> {
         // I can't think how to do better than this right now. -nikomatsakis
+        debug!(?placeholder_origin, ?sub, ?sup, "report_placeholder_failure");
         match placeholder_origin {
+            infer::Subtype(box ref trace)
+                if matches!(
+                    &trace.cause.code.peel_derives(),
+                    ObligationCauseCode::BindingObligation(..)
+                ) =>
+            {
+                // Hack to get around the borrow checker because trace.cause has an `Rc`.
+                if let ObligationCauseCode::BindingObligation(_, span) =
+                    &trace.cause.code.peel_derives()
+                {
+                    let span = *span;
+                    let mut err = self.report_concrete_failure(placeholder_origin, sub, sup);
+                    err.span_note(span, "the lifetime requirement is introduced here");
+                    err
+                } else {
+                    unreachable!()
+                }
+            }
             infer::Subtype(box trace) => {
                 let terr = TypeError::RegionsPlaceholderMismatch;
-                self.report_and_explain_type_error(trace, &terr)
+                return self.report_and_explain_type_error(trace, &terr);
             }
-
-            _ => self.report_concrete_failure(placeholder_origin, sub, sup),
+            _ => return self.report_concrete_failure(placeholder_origin, sub, sup),
         }
     }
 }