Rollup merge of #90667 - rukai:improve_static_lifetime_diagnostics, r=estebank

Improve diagnostics when a static lifetime is expected

Makes progress towards https://github.com/rust-lang/rust/issues/90600

The diagnostics here were previously entirely removed due to giving a misleading suggestion but if we instead provide an informative label in that same location it should better help the user understand the situation.

I included the example from the issue as it demonstrates an area where the diagnostics are still lacking.
Happy to remove that if its just adding noise atm.

1 files changed, 24 insertions, 41 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
index 0878f8550da..eb1c80ecb01 100644
--- 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
@@ -3,8 +3,6 @@
 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};
-use rustc_hir::intravisit::Visitor;
-use rustc_hir::FnRetTy;
 use rustc_middle::ty;
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
@@ -48,19 +46,24 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             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 == ty::ReStatic {
+            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, new_ty, new_ty_span, br, is_first, scope_def_id, is_impl_item) = (
-            anon_param_info.param,
-            anon_param_info.param_ty,
-            anon_param_info.param_ty_span,
-            anon_param_info.bound_region,
-            anon_param_info.is_first,
-            region_info.def_id,
-            region_info.is_impl_item,
-        );
+        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::BrAnon(_) => {}
             _ => {
@@ -75,26 +78,10 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             return None;
         }
 
-        if let Some((_, fndecl)) = find_anon_type(self.tcx(), anon, &br) {
-            if self.is_self_anon(is_first, scope_def_id) {
-                return None;
-            }
-
-            if let FnRetTy::Return(ty) = &fndecl.output {
-                let mut v = ty::TraitObjectVisitor(vec![], self.tcx().hir());
-                v.visit_ty(ty);
-
-                debug!("try_report_named_anon_conflict: ret ty {:?}", ty);
-                if sub == &ty::ReStatic
-                    && v.0.into_iter().any(|t| t.span.desugaring_kind().is_none())
-                {
-                    // If the failure is due to a `'static` requirement coming from a `dyn` or
-                    // `impl` Trait that *isn't* caused by `async fn` desugaring, handle this case
-                    // better in `static_impl_trait`.
-                    debug!("try_report_named_anon_conflict: impl Trait + 'static");
-                    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() {
@@ -114,16 +101,12 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         );
 
         diag.span_label(span, format!("lifetime `{}` required", named));
-        // Suggesting `'static` is nearly always incorrect, and can steer users
-        // down the wrong path.
-        if *named != ty::ReStatic {
-            diag.span_suggestion(
-                new_ty_span,
-                &format!("add explicit lifetime `{}` to {}", named, span_label_var),
-                new_ty.to_string(),
-                Applicability::Unspecified,
-            );
-        }
+        diag.span_suggestion(
+            new_ty_span,
+            &format!("add explicit lifetime `{}` to {}", named, span_label_var),
+            new_ty.to_string(),
+            Applicability::Unspecified,
+        );
 
         Some(diag)
     }