Rollup merge of #97720 - cjgillot:all-fresh, r=petrochenkov

Always create elided lifetime parameters for functions

Anonymous and elided lifetimes in functions are sometimes (async fns) --and sometimes not (regular fns)-- desugared to implicit generic parameters.

This difference of treatment makes it some downstream analyses more complicated to handle.  This step is a pre-requisite to perform lifetime elision resolution on AST.

There is currently an inconsistency in the treatment of argument-position impl-trait for functions and async fns:
```rust
trait Foo<'a> {}
fn foo(t: impl Foo<'_>) {} //~ ERROR missing lifetime specifier
async fn async_foo(t: impl Foo<'_>) {} //~ OK
fn bar(t: impl Iterator<Item = &'_ u8>) {} //~ ERROR missing lifetime specifier
async fn async_bar(t: impl Iterator<Item = &'_ u8>) {} //~ OK
```

The current implementation reports "missing lifetime specifier" on `foo`, but **accepts it** in `async_foo`.
This PR **proposes to accept** the anonymous lifetime in both cases as an extra generic lifetime parameter.
This change would be insta-stable, so let's ping t-lang.
Anonymous lifetimes in GAT bindings keep being forbidden:
```rust
fn foo(t: impl Foo<Assoc<'_> = Bar<'_>>) {}
                         ^^        ^^
                       forbidden   ok
```
I started a discussion here: https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Anonymous.20lifetimes.20in.20universal.20impl-trait/near/284968606

r? ``@petrochenkov``

clippy_lints/src/inherent_to_string.rs

@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::span_lint_and_help;
 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
 use clippy_utils::{get_trait_def_id, paths, return_ty, trait_ref_of_method};
 use if_chain::if_chain;
-use rustc_hir::{ImplItem, ImplItemKind};
+use rustc_hir::{GenericParamKind, ImplItem, ImplItemKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
@@ -102,7 +102,7 @@ impl<'tcx> LateLintPass<'tcx> for InherentToString {
             let decl = &signature.decl;
             if decl.implicit_self.has_implicit_self();
             if decl.inputs.len() == 1;
-            if impl_item.generics.params.is_empty();
+            if impl_item.generics.params.iter().all(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }));
 
             // Check if return type is String
             if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::String);

clippy_lints/src/lifetimes.rs

@@ -9,8 +9,8 @@ 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, ParamName, PolyTraitRef, PredicateOrigin,
-    TraitBoundModifier, TraitFn, TraitItem, TraitItemKind, Ty, TyKind, WherePredicate,
+    ImplItemKind, Item, ItemKind, LangItem, Lifetime, LifetimeName, LifetimeParamKind, 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;
@@ -338,7 +338,10 @@ fn could_use_elision<'tcx>(
 fn allowed_lts_from(named_generics: &[GenericParam<'_>]) -> FxHashSet<RefLt> {
     let mut allowed_lts = FxHashSet::default();
     for par in named_generics.iter() {
-        if let GenericParamKind::Lifetime { .. } = par.kind {
+        if let GenericParamKind::Lifetime {
+            kind: LifetimeParamKind::Explicit,
+        } = par.kind
+        {
             allowed_lts.insert(RefLt::Named(par.name.ident().name));
         }
     }
@@ -379,6 +382,7 @@ impl<'a, 'tcx> RefVisitor<'a, 'tcx> {
                 self.lts.push(RefLt::Static);
             } else if let LifetimeName::Param(_, ParamName::Fresh) = lt.name {
                 // Fresh lifetimes generated should be ignored.
+                self.lts.push(RefLt::Unnamed);
             } else if lt.is_elided() {
                 self.lts.push(RefLt::Unnamed);
             } else {

clippy_lints/src/ptr.rs

@@ -495,12 +495,13 @@ fn check_mut_from_ref<'tcx>(cx: &LateContext<'tcx>, sig: &FnSig<'_>, body: Optio
     if let FnRetTy::Return(ty) = sig.decl.output
         && let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty)
     {
+        let out_region = cx.tcx.named_region(out.hir_id);
         let args: Option<Vec<_>> = sig
             .decl
             .inputs
             .iter()
             .filter_map(get_rptr_lm)
-            .filter(|&(lt, _, _)| lt.name == out.name)
+            .filter(|&(lt, _, _)| cx.tcx.named_region(lt.hir_id) == out_region)
             .map(|(_, mutability, span)| (mutability == Mutability::Not).then(|| span))
             .collect();
         if let Some(args) = args

clippy_lints/src/types/borrowed_box.rs

@@ -31,7 +31,7 @@ pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, lt: &Lifetime, m
                         return false;
                     }
 
-                    let ltopt = if lt.is_elided() {
+                    let ltopt = if lt.name.is_anonymous() {
                         String::new()
                     } else {
                         format!("{} ", lt.name.ident().as_str())