Auto merge of #9556 - evantypanski:et/issue-9369, r=Alexendoo

[`redundant_closure`] Fix suggestion causes error for `impl FnMut`

Fixes #9369

changelog: [`redundant_closure`] Fix suggestion causes error with `impl FnMut` types

clippy_lints/src/eta_reduction.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::higher::VecArgs;
 use clippy_utils::source::snippet_opt;
-use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
 use clippy_utils::usage::local_used_after_expr;
 use clippy_utils::{higher, is_adjusted, path_to_local, path_to_local_id};
 use if_chain::if_chain;
@@ -11,7 +11,7 @@
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc_middle::ty::binding::BindingMode;
-use rustc_middle::ty::{self, ClosureKind, Ty, TypeVisitable};
+use rustc_middle::ty::{self, Ty, TypeVisitable};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::sym;
 
@@ -122,16 +122,13 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
             then {
                 span_lint_and_then(cx, REDUNDANT_CLOSURE, expr.span, "redundant closure", |diag| {
                     if let Some(mut snippet) = snippet_opt(cx, callee.span) {
-                        if_chain! {
-                            if let ty::Closure(_, substs) = callee_ty.peel_refs().kind();
-                            if substs.as_closure().kind() == ClosureKind::FnMut;
-                            if path_to_local(callee).map_or(false, |l| local_used_after_expr(cx, l, expr));
-
-                            then {
+                        if let Some(fn_mut_id) = cx.tcx.lang_items().fn_mut_trait()
+                            && implements_trait(cx, callee_ty.peel_refs(), fn_mut_id, &[])
+                            && path_to_local(callee).map_or(false, |l| local_used_after_expr(cx, l, expr))
+                        {
                                 // Mutable closure is used after current expr; we cannot consume it.
                                 snippet = format!("&mut {snippet}");
                         }
-                        }
                         diag.span_suggestion(
                             expr.span,
                             "replace the closure with the function itself",

tests/ui/eta.fixed

@@ -303,3 +303,16 @@ fn not_general_enough() {
     fn f(_: impl FnMut(&Path) -> std::io::Result<()>) {}
     f(|path| std::fs::remove_file(path));
 }
+
+// https://github.com/rust-lang/rust-clippy/issues/9369
+pub fn mutable_impl_fn_mut(mut f: impl FnMut(), mut f_used_once: impl FnMut()) -> impl FnMut() {
+    fn takes_fn_mut(_: impl FnMut()) {}
+    takes_fn_mut(&mut f);
+
+    fn takes_fn_once(_: impl FnOnce()) {}
+    takes_fn_once(&mut f);
+
+    f();
+
+    move || takes_fn_mut(&mut f_used_once)
+}

tests/ui/eta.rs

@@ -303,3 +303,16 @@ fn not_general_enough() {
     fn f(_: impl FnMut(&Path) -> std::io::Result<()>) {}
     f(|path| std::fs::remove_file(path));
 }
+
+// https://github.com/rust-lang/rust-clippy/issues/9369
+pub fn mutable_impl_fn_mut(mut f: impl FnMut(), mut f_used_once: impl FnMut()) -> impl FnMut() {
+    fn takes_fn_mut(_: impl FnMut()) {}
+    takes_fn_mut(|| f());
+
+    fn takes_fn_once(_: impl FnOnce()) {}
+    takes_fn_once(|| f());
+
+    f();
+
+    move || takes_fn_mut(|| f_used_once())
+}

tests/ui/eta.stderr

@@ -116,5 +116,23 @@ error: redundant closure
 LL |         Some(1).map(|n| in_loop(n));
    |                     ^^^^^^^^^^^^^^ help: replace the closure with the function itself: `in_loop`
 
-error: aborting due to 19 previous errors
+error: redundant closure
+  --> $DIR/eta.rs:310:18
+   |
+LL |     takes_fn_mut(|| f());
+   |                  ^^^^^^ help: replace the closure with the function itself: `&mut f`
+
+error: redundant closure
+  --> $DIR/eta.rs:313:19
+   |
+LL |     takes_fn_once(|| f());
+   |                   ^^^^^^ help: replace the closure with the function itself: `&mut f`
+
+error: redundant closure
+  --> $DIR/eta.rs:317:26
+   |
+LL |     move || takes_fn_mut(|| f_used_once())
+   |                          ^^^^^^^^^^^^^^^^ help: replace the closure with the function itself: `&mut f_used_once`
+
+error: aborting due to 22 previous errors