Auto merge of #13286 - smoelius:elidable-impl-lifetimes, r=Alexendoo

Extend `needless_lifetimes` to suggest eliding `impl` lifetimes

Example:
```
error: the following explicit lifetimes could be elided: 'a
  --> tests/ui/needless_lifetimes.rs:332:10
   |
LL |     impl<'a> Foo for Baz<'a> {}
   |          ^^              ^^
   |
help: elide the lifetimes
   |
LL -     impl<'a> Foo for Baz<'a> {}
LL +     impl Foo for Baz<'_> {}
```
The main change is in how `impl` lifetime uses are tracked. Previously, a hashmap was created, and lifetimes were removed from the hashmap as their uses were discovered. However, the uses are needed to generate elision suggestions. So, now, uses are added to the hashmap as they are discovered.

The PR is currently organized as six commits, which I think are self-explanatory:
- Extend `needless_lifetimes` to suggest eliding `impl` lifetimes
- Reorder functions _[not strictly necessary, but IMHO, the code is better structured as a result]_
- Fix lifetime tests
- Fix non-lifetime tests
- Fix `clippy_lints` and `clippy_utils`
- Fix typo in `needless_lifetimes` test

r? `@Alexendoo` (I think you are `needless_lifetimes`' primary author? Sorry if I have this wrong.)

---

changelog: Extend `needless_lifetimes` to suggest eliding `impl` lifetimes

Author: bors

Diff for: clippy_lints/src/booleans.rs

@@ -205,7 +205,7 @@ struct Hir2Qmm<'a, 'tcx, 'v> {
     cx: &'a LateContext<'tcx>,
 }
 
-impl<'a, 'tcx, 'v> Hir2Qmm<'a, 'tcx, 'v> {
+impl<'v> Hir2Qmm<'_, '_, 'v> {
     fn extract(&mut self, op: BinOpKind, a: &[&'v Expr<'_>], mut v: Vec<Bool>) -> Result<Vec<Bool>, String> {
         for a in a {
             if let ExprKind::Binary(binop, lhs, rhs) = &a.kind {
@@ -292,7 +292,7 @@ struct SuggestContext<'a, 'tcx, 'v> {
     output: String,
 }
 
-impl<'a, 'tcx, 'v> SuggestContext<'a, 'tcx, 'v> {
+impl SuggestContext<'_, '_, '_> {
     fn recurse(&mut self, suggestion: &Bool) -> Option<()> {
         use quine_mc_cluskey::Bool::{And, False, Not, Or, Term, True};
         match suggestion {
@@ -475,7 +475,7 @@ fn terminal_stats(b: &Bool) -> Stats {
     stats
 }
 
-impl<'a, 'tcx> NonminimalBoolVisitor<'a, 'tcx> {
+impl<'tcx> NonminimalBoolVisitor<'_, 'tcx> {
     fn bool_expr(&self, e: &'tcx Expr<'_>) {
         let mut h2q = Hir2Qmm {
             terminals: Vec::new(),
@@ -582,7 +582,7 @@ impl<'a, 'tcx> NonminimalBoolVisitor<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for NonminimalBoolVisitor<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for NonminimalBoolVisitor<'_, 'tcx> {
     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
         if !e.span.from_expansion() {
             match &e.kind {

Diff for: clippy_lints/src/box_default.rs

@@ -91,7 +91,7 @@ fn is_local_vec_expn(cx: &LateContext<'_>, expr: &Expr<'_>, ref_expr: &Expr<'_>)
 #[derive(Default)]
 struct InferVisitor(bool);
 
-impl<'tcx> Visitor<'tcx> for InferVisitor {
+impl Visitor<'_> for InferVisitor {
     fn visit_ty(&mut self, t: &Ty<'_>) {
         self.0 |= matches!(t.kind, TyKind::Infer | TyKind::OpaqueDef(..) | TyKind::TraitObject(..));
         if !self.0 {

Diff for: clippy_lints/src/checked_conversions.rs

@@ -48,7 +48,7 @@ impl CheckedConversions {
 
 impl_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
 
-impl<'tcx> LateLintPass<'tcx> for CheckedConversions {
+impl LateLintPass<'_> for CheckedConversions {
     fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
         if let ExprKind::Binary(op, lhs, rhs) = item.kind
             && let (lt1, gt1, op2) = match op.node {

Diff for: clippy_lints/src/default_numeric_fallback.rs

@@ -119,7 +119,7 @@ impl<'a, 'tcx> NumericFallbackVisitor<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for NumericFallbackVisitor<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for NumericFallbackVisitor<'_, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
         match &expr.kind {
             ExprKind::Block(

Diff for: clippy_lints/src/doc/mod.rs

@@ -970,7 +970,7 @@ impl<'a, 'tcx> FindPanicUnwrap<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for FindPanicUnwrap<'_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {

Diff for: clippy_lints/src/empty_enum.rs

@@ -60,7 +60,7 @@ declare_clippy_lint! {
 
 declare_lint_pass!(EmptyEnum => [EMPTY_ENUM]);
 
-impl<'tcx> LateLintPass<'tcx> for EmptyEnum {
+impl LateLintPass<'_> for EmptyEnum {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
         if let ItemKind::Enum(..) = item.kind
             // Only suggest the `never_type` if the feature is enabled

Diff for: clippy_lints/src/escape.rs

@@ -141,7 +141,7 @@ fn is_argument(tcx: TyCtxt<'_>, id: HirId) -> bool {
     matches!(tcx.parent_hir_node(id), Node::Param(_))
 }
 
-impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
+impl<'tcx> Delegate<'tcx> for EscapeDelegate<'_, 'tcx> {
     fn consume(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
         if cmt.place.projections.is_empty() {
             if let PlaceBase::Local(lid) = cmt.place.base {
@@ -188,7 +188,7 @@ impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
     fn fake_read(&mut self, _: &PlaceWithHirId<'tcx>, _: FakeReadCause, _: HirId) {}
 }
 
-impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
+impl<'tcx> EscapeDelegate<'_, 'tcx> {
     fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
         // Large types need to be boxed to avoid stack overflows.
         if let Some(boxed_ty) = ty.boxed_ty() {

Diff for: clippy_lints/src/excessive_nesting.rs

@@ -135,7 +135,7 @@ impl NestingVisitor<'_, '_> {
     }
 }
 
-impl<'conf, 'cx> Visitor<'_> for NestingVisitor<'conf, 'cx> {
+impl Visitor<'_> for NestingVisitor<'_, '_> {
     fn visit_block(&mut self, block: &Block) {
         if block.span.from_expansion() {
             return;

Diff for: clippy_lints/src/extra_unused_type_parameters.rs

@@ -193,7 +193,7 @@ fn bound_to_trait_def_id(bound: &GenericBound<'_>) -> Option<LocalDefId> {
     bound.trait_ref()?.trait_def_id()?.as_local()
 }
 
-impl<'cx, 'tcx> Visitor<'tcx> for TypeWalker<'cx, 'tcx> {
+impl<'tcx> Visitor<'tcx> for TypeWalker<'_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
     fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {

Diff for: clippy_lints/src/fallible_impl_from.rs

@@ -73,7 +73,7 @@ fn lint_impl_body(cx: &LateContext<'_>, impl_span: Span, impl_items: &[hir::Impl
         result: Vec<Span>,
     }
 
-    impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
+    impl<'tcx> Visitor<'tcx> for FindPanicUnwrap<'_, 'tcx> {
         fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
             if let Some(macro_call) = root_macro_call_first_node(self.lcx, expr) {
                 if is_panic(self.lcx, macro_call.def_id) {

Diff for: clippy_lints/src/format_args.rs

@@ -219,7 +219,7 @@ struct FormatArgsExpr<'a, 'tcx> {
     ignore_mixed: bool,
 }
 
-impl<'a, 'tcx> FormatArgsExpr<'a, 'tcx> {
+impl FormatArgsExpr<'_, '_> {
     fn check_templates(&self) {
         for piece in &self.format_args.template {
             if let FormatArgsPiece::Placeholder(placeholder) = piece

Diff for: clippy_lints/src/format_impl.rs

@@ -148,7 +148,7 @@ struct FormatImplExpr<'a, 'tcx> {
     format_trait_impl: FormatTraitNames,
 }
 
-impl<'a, 'tcx> FormatImplExpr<'a, 'tcx> {
+impl FormatImplExpr<'_, '_> {
     fn check_to_string_in_display(&self) {
         if self.format_trait_impl.name == sym::Display
             && let ExprKind::MethodCall(path, self_arg, ..) = self.expr.kind

Diff for: clippy_lints/src/from_over_into.rs

@@ -126,7 +126,7 @@ struct SelfFinder<'a, 'tcx> {
     invalid: bool,
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for SelfFinder<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for SelfFinder<'_, 'tcx> {
     type NestedFilter = OnlyBodies;
 
     fn nested_visit_map(&mut self) -> Self::Map {

Diff for: clippy_lints/src/implicit_hasher.rs

@@ -281,7 +281,7 @@ impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'_, 'tcx> {
     fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
         if let Some(target) = ImplicitHasherType::new(self.cx, t) {
             self.found.push(target);
@@ -318,7 +318,7 @@ impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
     }
 }
 
-impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
+impl<'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'_, '_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
     fn visit_body(&mut self, body: &Body<'tcx>) {

Diff for: clippy_lints/src/index_refutable_slice.rs

@@ -226,7 +226,7 @@ struct SliceIndexLintingVisitor<'a, 'tcx> {
     max_suggested_slice: u64,
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for SliceIndexLintingVisitor<'a, 'tcx> {
+impl<'tcx> Visitor<'tcx> for SliceIndexLintingVisitor<'_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
     fn nested_visit_map(&mut self) -> Self::Map {