1 files changed, 116 insertions, 0 deletions
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs
new file mode 100644
index 000000000..76cb76d9f
--- /dev/null
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/named_anon_conflict.rs
@@ -0,0 +1,116 @@
+//! Error Reporting for Anonymous Region Lifetime Errors
+//! where one region is named and the other is anonymous.
+use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
+use crate::infer::error_reporting::nice_region_error::NiceRegionError;
+use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_middle::ty;
+use rustc_span::symbol::kw;
+
+impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
+    /// When given a `ConcreteFailure` for a function with parameters containing a named region and
+    /// an anonymous region, emit an descriptive diagnostic error.
+    pub(super) fn try_report_named_anon_conflict(
+        &self,
+    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
+        let (span, sub, sup) = self.regions()?;
+
+        debug!(
+            "try_report_named_anon_conflict(sub={:?}, sup={:?}, error={:?})",
+            sub, sup, self.error,
+        );
+
+        // Determine whether the sub and sup consist of one named region ('a)
+        // and one anonymous (elided) region. If so, find the parameter arg
+        // where the anonymous region appears (there must always be one; we
+        // only introduced anonymous regions in parameters) as well as a
+        // version new_ty of its type where the anonymous region is replaced
+        // with the named one.
+        let (named, anon, anon_param_info, region_info) = if sub.has_name()
+            && self.tcx().is_suitable_region(sup).is_some()
+            && self.find_param_with_region(sup, sub).is_some()
+        {
+            (
+                sub,
+                sup,
+                self.find_param_with_region(sup, sub).unwrap(),
+                self.tcx().is_suitable_region(sup).unwrap(),
+            )
+        } else if sup.has_name()
+            && self.tcx().is_suitable_region(sub).is_some()
+            && self.find_param_with_region(sub, sup).is_some()
+        {
+            (
+                sup,
+                sub,
+                self.find_param_with_region(sub, sup).unwrap(),
+                self.tcx().is_suitable_region(sub).unwrap(),
+            )
+        } else {
+            return None; // inapplicable
+        };
+
+        // Suggesting to add a `'static` lifetime to a parameter is nearly always incorrect,
+        // and can steer users down the wrong path.
+        if named.is_static() {
+            return None;
+        }
+
+        debug!("try_report_named_anon_conflict: named = {:?}", named);
+        debug!("try_report_named_anon_conflict: anon_param_info = {:?}", anon_param_info);
+        debug!("try_report_named_anon_conflict: region_info = {:?}", region_info);
+
+        let param = anon_param_info.param;
+        let new_ty = anon_param_info.param_ty;
+        let new_ty_span = anon_param_info.param_ty_span;
+        let br = anon_param_info.bound_region;
+        let is_first = anon_param_info.is_first;
+        let scope_def_id = region_info.def_id;
+        let is_impl_item = region_info.is_impl_item;
+
+        match br {
+            ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) => {}
+            _ => {
+                /* not an anonymous region */
+                debug!("try_report_named_anon_conflict: not an anonymous region");
+                return None;
+            }
+        }
+
+        if is_impl_item {
+            debug!("try_report_named_anon_conflict: impl item, bail out");
+            return None;
+        }
+
+        if find_anon_type(self.tcx(), anon, &br).is_some()
+            && self.is_self_anon(is_first, scope_def_id)
+        {
+            return None;
+        }
+
+        let (error_var, span_label_var) = match param.pat.simple_ident() {
+            Some(simple_ident) => (
+                format!("the type of `{}`", simple_ident),
+                format!("the type of `{}`", simple_ident),
+            ),
+            None => ("parameter type".to_owned(), "type".to_owned()),
+        };
+
+        let mut diag = struct_span_err!(
+            self.tcx().sess,
+            span,
+            E0621,
+            "explicit lifetime required in {}",
+            error_var
+        );
+
+        diag.span_label(span, format!("lifetime `{}` required", named));
+        diag.span_suggestion(
+            new_ty_span,
+            &format!("add explicit lifetime `{}` to {}", named, span_label_var),
+            new_ty,
+            Applicability::Unspecified,
+        );
+
+        Some(diag)
+    }
+}