needless_lifetimes: ignore lifetimes in explicit self types

Alexendoo · Alexendoo · commit 47e45edb3d45 · 2022-01-14T15:16:18.000Z
diff --git a/clippy_lints/src/lifetimes.rs b/clippy_lints/src/lifetimes.rs
@@ -15,7 +15,7 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::map::Map;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use rustc_span::symbol::{kw, Symbol};
+use rustc_span::symbol::{kw, Ident, Symbol};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -85,7 +85,7 @@ declare_lint_pass!(Lifetimes => [NEEDLESS_LIFETIMES, EXTRA_UNUSED_LIFETIMES]);
 impl<'tcx> LateLintPass<'tcx> for Lifetimes {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
         if let ItemKind::Fn(ref sig, ref generics, id) = item.kind {
-            check_fn_inner(cx, sig.decl, Some(id), generics, item.span, true);
+            check_fn_inner(cx, sig.decl, Some(id), None, generics, item.span, true);
         }
     }
 
@@ -96,6 +96,7 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
                 cx,
                 sig.decl,
                 Some(id),
+                None,
                 &item.generics,
                 item.span,
                 report_extra_lifetimes,
@@ -105,11 +106,11 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
 
     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
         if let TraitItemKind::Fn(ref sig, ref body) = item.kind {
-            let body = match *body {
-                TraitFn::Required(_) => None,
-                TraitFn::Provided(id) => Some(id),
+            let (body, trait_sig) = match *body {
+                TraitFn::Required(sig) => (None, Some(sig)),
+                TraitFn::Provided(id) => (Some(id), None),
             };
-            check_fn_inner(cx, sig.decl, body, &item.generics, item.span, true);
+            check_fn_inner(cx, sig.decl, body, trait_sig, &item.generics, item.span, true);
         }
     }
 }
@@ -126,6 +127,7 @@ fn check_fn_inner<'tcx>(
     cx: &LateContext<'tcx>,
     decl: &'tcx FnDecl<'_>,
     body: Option<BodyId>,
+    trait_sig: Option<&[Ident]>,
     generics: &'tcx Generics<'_>,
     span: Span,
     report_extra_lifetimes: bool,
@@ -167,7 +169,7 @@ fn check_fn_inner<'tcx>(
             }
         }
     }
-    if could_use_elision(cx, decl, body, generics.params) {
+    if could_use_elision(cx, decl, body, trait_sig, generics.params) {
         span_lint(
             cx,
             NEEDLESS_LIFETIMES,
@@ -181,10 +183,31 @@ fn check_fn_inner<'tcx>(
     }
 }
 
+// elision doesn't work for explicit self types, see rust-lang/rust#69064
+fn explicit_self_type<'tcx>(cx: &LateContext<'tcx>, func: &FnDecl<'tcx>, ident: Option<Ident>) -> bool {
+    if_chain! {
+        if let Some(ident) = ident;
+        if ident.name == kw::SelfLower;
+        if !func.implicit_self.has_implicit_self();
+
+        if let Some(self_ty) = func.inputs.first();
+        then {
+            let mut visitor = RefVisitor::new(cx);
+            visitor.visit_ty(self_ty);
+
+            !visitor.all_lts().is_empty()
+        }
+        else {
+            false
+        }
+    }
+}
+
 fn could_use_elision<'tcx>(
     cx: &LateContext<'tcx>,
     func: &'tcx FnDecl<'_>,
     body: Option<BodyId>,
+    trait_sig: Option<&[Ident]>,
     named_generics: &'tcx [GenericParam<'_>],
 ) -> bool {
     // There are two scenarios where elision works:
@@ -235,11 +258,24 @@ fn could_use_elision<'tcx>(
     let input_lts = input_visitor.lts;
     let output_lts = output_visitor.lts;
 
+    if let Some(trait_sig) = trait_sig {
+        if explicit_self_type(cx, func, trait_sig.first().copied()) {
+            return false;
+        }
+    }
+
     if let Some(body_id) = body {
+        let body = cx.tcx.hir().body(body_id);
+
+        let first_ident = body.params.first().and_then(|param| param.pat.simple_ident());
+        if explicit_self_type(cx, func, first_ident) {
+            return false;
+        }
+
         let mut checker = BodyLifetimeChecker {
             lifetimes_used_in_body: false,
         };
-        checker.visit_expr(&cx.tcx.hir().body(body_id).value);
+        checker.visit_expr(&body.value);
         if checker.lifetimes_used_in_body {
             return false;
         }
diff --git a/tests/ui/needless_lifetimes.rs b/tests/ui/needless_lifetimes.rs
@@ -369,4 +369,47 @@ mod issue6159 {
     }
 }
 
+mod issue7296 {
+    use std::rc::Rc;
+    use std::sync::Arc;
+
+    struct Foo;
+    impl Foo {
+        fn implicit<'a>(&'a self) -> &'a () {
+            &()
+        }
+        fn implicit_mut<'a>(&'a mut self) -> &'a () {
+            &()
+        }
+
+        fn explicit<'a>(self: &'a Arc<Self>) -> &'a () {
+            &()
+        }
+        fn explicit_mut<'a>(self: &'a mut Rc<Self>) -> &'a () {
+            &()
+        }
+
+        fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
+            &()
+        }
+    }
+
+    trait Bar {
+        fn implicit<'a>(&'a self) -> &'a ();
+        fn implicit_provided<'a>(&'a self) -> &'a () {
+            &()
+        }
+
+        fn explicit<'a>(self: &'a Arc<Self>) -> &'a ();
+        fn explicit_provided<'a>(self: &'a Arc<Self>) -> &'a () {
+            &()
+        }
+
+        fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a ();
+        fn lifetime_elsewhere_provided<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
+            &()
+        }
+    }
+}
+
 fn main() {}
diff --git a/tests/ui/needless_lifetimes.stderr b/tests/ui/needless_lifetimes.stderr
@@ -150,5 +150,55 @@ error: explicit lifetimes given in parameter types where they could be elided (o
 LL |     fn nested_fn_pointer_4<'a>(_: &'a i32) -> impl Fn(fn(&i32)) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 25 previous errors
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:378:9
+   |
+LL |         fn implicit<'a>(&'a self) -> &'a () {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:381:9
+   |
+LL |         fn implicit_mut<'a>(&'a mut self) -> &'a () {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:392:9
+   |
+LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: local variable doesn't need to be boxed here
+  --> $DIR/needless_lifetimes.rs:392:35
+   |
+LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
+   |                                   ^^^^
+   |
+   = note: `-D clippy::boxed-local` implied by `-D warnings`
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:398:9
+   |
+LL |         fn implicit<'a>(&'a self) -> &'a ();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:399:9
+   |
+LL |         fn implicit_provided<'a>(&'a self) -> &'a () {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:408:9
+   |
+LL |         fn lifetime_elsewhere<'a>(self: Box<Self>, here: &'a ()) -> &'a ();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)
+  --> $DIR/needless_lifetimes.rs:409:9
+   |
+LL |         fn lifetime_elsewhere_provided<'a>(self: Box<Self>, here: &'a ()) -> &'a () {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 33 previous errors
 
