Auto merge of rust-lang#97313 - cjgillot:ast-lifetimes-anon, r=petrochenkov

Resolve function lifetime elision on the AST

~Based on rust-lang#97720

Lifetime elision for functions is purely syntactic in nature, so can be resolved on the AST.
This PR replicates the elision logic and diagnostics on the AST, and replaces HIR-based resolution by a `delay_span_bug`.

This refactor allows for more consistent diagnostics, which don't have to guess the original code from HIR.

r? `@petrochenkov`

Author: bors

clippy_lints/src/lifetimes.rs

@@ -9,12 +9,14 @@ use rustc_hir::intravisit::{
 use rustc_hir::FnRetTy::Return;
 use rustc_hir::{
     BareFnTy, BodyId, FnDecl, GenericArg, GenericBound, GenericParam, GenericParamKind, Generics, Impl, ImplItem,
-    ImplItemKind, Item, ItemKind, LangItem, Lifetime, LifetimeName, LifetimeParamKind, ParamName, PolyTraitRef,
-    PredicateOrigin, TraitBoundModifier, TraitFn, TraitItem, TraitItemKind, Ty, TyKind, WherePredicate,
+    ImplItemKind, Item, ItemKind, LangItem, Lifetime, LifetimeName, ParamName, PolyTraitRef, PredicateOrigin,
+    TraitBoundModifier, TraitFn, TraitItem, TraitItemKind, Ty, TyKind, WherePredicate,
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter as middle_nested_filter;
+use rustc_middle::ty::TyCtxt;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::{kw, Ident, Symbol};
 
@@ -129,7 +131,7 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
 enum RefLt {
     Unnamed,
     Static,
-    Named(Symbol),
+    Named(LocalDefId),
 }
 
 fn check_fn_inner<'tcx>(
@@ -232,7 +234,7 @@ fn could_use_elision<'tcx>(
     // level of the current item.
 
     // check named LTs
-    let allowed_lts = allowed_lts_from(named_generics);
+    let allowed_lts = allowed_lts_from(cx.tcx, named_generics);
 
     // these will collect all the lifetimes for references in arg/return types
     let mut input_visitor = RefVisitor::new(cx);
@@ -254,22 +256,6 @@ fn could_use_elision<'tcx>(
         return false;
     }
 
-    if allowed_lts
-        .intersection(
-            &input_visitor
-                .nested_elision_site_lts
-                .iter()
-                .chain(output_visitor.nested_elision_site_lts.iter())
-                .cloned()
-                .filter(|v| matches!(v, RefLt::Named(_)))
-                .collect(),
-        )
-        .next()
-        .is_some()
-    {
-        return false;
-    }
-
     let input_lts = input_visitor.lts;
     let output_lts = output_visitor.lts;
 
@@ -303,6 +289,31 @@ fn could_use_elision<'tcx>(
         }
     }
 
+    // check for higher-ranked trait bounds
+    if !input_visitor.nested_elision_site_lts.is_empty() || !output_visitor.nested_elision_site_lts.is_empty() {
+        let allowed_lts: FxHashSet<_> = allowed_lts
+            .iter()
+            .filter_map(|lt| match lt {
+                RefLt::Named(def_id) => Some(cx.tcx.item_name(def_id.to_def_id())),
+                _ => None,
+            })
+            .collect();
+        for lt in input_visitor.nested_elision_site_lts {
+            if let RefLt::Named(def_id) = lt {
+                if allowed_lts.contains(&cx.tcx.item_name(def_id.to_def_id())) {
+                    return false;
+                }
+            }
+        }
+        for lt in output_visitor.nested_elision_site_lts {
+            if let RefLt::Named(def_id) = lt {
+                if allowed_lts.contains(&cx.tcx.item_name(def_id.to_def_id())) {
+                    return false;
+                }
+            }
+        }
+    }
+
     // no input lifetimes? easy case!
     if input_lts.is_empty() {
         false
@@ -335,14 +346,11 @@ fn could_use_elision<'tcx>(
     }
 }
 
-fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
+fn allowed_lts_from(tcx: TyCtxt<'_>, named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
     let mut allowed_lts = FxHashSet::default();
     for par in named_generics.iter() {
-        if let GenericParamKind::Lifetime {
-            kind: LifetimeParamKind::Explicit,
-        } = par.kind
-        {
-            allowed_lts.insert(RefLt::Named(par.name.ident().name));
+        if let GenericParamKind::Lifetime { .. } = par.kind {
+            allowed_lts.insert(RefLt::Named(tcx.hir().local_def_id(par.hir_id)));
         }
     }
     allowed_lts.insert(RefLt::Unnamed);
@@ -385,8 +393,10 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
                 self.lts.push(RefLt::Unnamed);
             } else if lt.is_elided() {
                 self.lts.push(RefLt::Unnamed);
+            } else if let LifetimeName::Param(def_id, _) = lt.name {
+                self.lts.push(RefLt::Named(def_id));
             } else {
-                self.lts.push(RefLt::Named(lt.name.ident().name));
+                self.lts.push(RefLt::Unnamed);
             }
         } else {
             self.lts.push(RefLt::Unnamed);
@@ -434,10 +444,15 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
             TyKind::OpaqueDef(item, bounds) => {
                 let map = self.cx.tcx.hir();
                 let item = map.item(item);
+                let len = self.lts.len();
                 walk_item(self, item);
-                walk_ty(self, ty);
+                self.lts.truncate(len);
                 self.lts.extend(bounds.iter().filter_map(|bound| match bound {
-                    GenericArg::Lifetime(l) => Some(RefLt::Named(l.name.ident().name)),
+                    GenericArg::Lifetime(l) => Some(if let LifetimeName::Param(def_id, _) = l.name {
+                        RefLt::Named(def_id)
+                    } else {
+                        RefLt::Unnamed
+                    }),
                     _ => None,
                 }));
             },
@@ -456,9 +471,8 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
                 }
                 return;
             },
-            _ => (),
+            _ => walk_ty(self, ty),
         }
-        walk_ty(self, ty);
     }
 }
 
@@ -477,7 +491,7 @@ fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, generics: &'tcx Generics<'_
                     return true;
                 }
                 // if the bounds define new lifetimes, they are fine to occur
-                let allowed_lts = allowed_lts_from(pred.bound_generic_params);
+                let allowed_lts = allowed_lts_from(cx.tcx, pred.bound_generic_params);
                 // now walk the bounds
                 for bound in pred.bounds.iter() {
                     walk_param_bound(&mut visitor, bound);