Simplify get_enclosing_loop_or_multi_call_closure

Author: Jarcho

clippy_utils/src/lib.rs

@@ -113,10 +113,7 @@ use visitors::Visitable;
 
 use crate::consts::{constant, mir_to_const, Constant};
 use crate::higher::Range;
-use crate::ty::{
-    adt_and_variant_of_res, can_partially_move_ty, expr_sig, is_copy, is_recursively_primitive_type,
-    ty_is_fn_once_param,
-};
+use crate::ty::{adt_and_variant_of_res, can_partially_move_ty, expr_sig, is_copy, is_recursively_primitive_type};
 use crate::visitors::for_each_expr;
 
 use rustc_middle::hir::nested_filter;
@@ -1345,46 +1342,12 @@ pub fn get_enclosing_loop_or_multi_call_closure<'tcx>(
     for (_, node) in cx.tcx.hir().parent_iter(expr.hir_id) {
         match node {
             Node::Expr(e) => match e.kind {
-                ExprKind::Closure { .. } => {
+                ExprKind::Closure { .. }
                     if let rustc_ty::Closure(_, subs) = cx.typeck_results().expr_ty(e).kind()
-                        && subs.as_closure().kind() == ClosureKind::FnOnce
-                    {
-                        continue;
-                    }
-                    let is_once = walk_to_expr_usage(cx, e, |node, id| {
-                        let Node::Expr(e) = node else {
-                            return None;
-                        };
-                        match e.kind {
-                            ExprKind::Call(f, _) if f.hir_id == id => Some(()),
-                            ExprKind::Call(f, args) => {
-                                let i = args.iter().position(|arg| arg.hir_id == id)?;
-                                let sig = expr_sig(cx, f)?;
-                                let predicates = sig
-                                    .predicates_id()
-                                    .map_or(cx.param_env, |id| cx.tcx.param_env(id))
-                                    .caller_bounds();
-                                sig.input(i).and_then(|ty| {
-                                    ty_is_fn_once_param(cx.tcx, ty.skip_binder(), predicates).then_some(())
-                                })
-                            },
-                            ExprKind::MethodCall(_, receiver, args, _) => {
-                                let i = std::iter::once(receiver)
-                                    .chain(args.iter())
-                                    .position(|arg| arg.hir_id == id)?;
-                                let id = cx.typeck_results().type_dependent_def_id(e.hir_id)?;
-                                let ty = cx.tcx.fn_sig(id).instantiate_identity().skip_binder().inputs()[i];
-                                ty_is_fn_once_param(cx.tcx, ty, cx.tcx.param_env(id).caller_bounds()).then_some(())
-                            },
-                            _ => None,
-                        }
-                    })
-                    .is_some();
-                    if !is_once {
-                        return Some(e);
-                    }
-                },
-                ExprKind::Loop(..) => return Some(e),
+                        && subs.as_closure().kind() == ClosureKind::FnOnce => {},
+
+                // Note: A closure's kind is determined by how it's used, not it's captures.
+                ExprKind::Closure { .. } | ExprKind::Loop(..) => return Some(e),
                 _ => (),
             },
             Node::Stmt(_) | Node::Block(_) | Node::Local(_) | Node::Arm(_) => (),

clippy_utils/src/ty.rs

@@ -972,35 +972,6 @@ pub fn adt_and_variant_of_res<'tcx>(cx: &LateContext<'tcx>, res: Res) -> Option<
     }
 }
 
-/// Checks if the type is a type parameter implementing `FnOnce`, but not `FnMut`.
-pub fn ty_is_fn_once_param<'tcx>(tcx: TyCtxt<'_>, ty: Ty<'tcx>, predicates: &'tcx [ty::Clause<'_>]) -> bool {
-    let ty::Param(ty) = *ty.kind() else {
-        return false;
-    };
-    let lang = tcx.lang_items();
-    let (Some(fn_once_id), Some(fn_mut_id), Some(fn_id)) = (lang.fn_once_trait(), lang.fn_mut_trait(), lang.fn_trait())
-    else {
-        return false;
-    };
-    predicates
-        .iter()
-        .try_fold(false, |found, p| {
-            if let ty::ClauseKind::Trait(p) = p.kind().skip_binder()
-                && let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
-                && ty.index == self_ty.index
-            {
-                // This should use `super_traits_of`, but that's a private function.
-                if p.trait_ref.def_id == fn_once_id {
-                    return Some(true);
-                } else if p.trait_ref.def_id == fn_mut_id || p.trait_ref.def_id == fn_id {
-                    return None;
-                }
-            }
-            Some(found)
-        })
-        .unwrap_or(false)
-}
-
 /// Comes up with an "at least" guesstimate for the type's size, not taking into
 /// account the layout of type parameters.
 pub fn approx_ty_size<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> u64 {

tests/ui/while_let_on_iterator.fixed

@@ -406,7 +406,7 @@ fn issue_8113() {
 fn fn_once_closure() {
     let mut it = 0..10;
     (|| {
-        for x in it {
+        for x in it.by_ref() {
             if x % 2 == 0 {
                 break;
             }
@@ -441,7 +441,19 @@ fn fn_once_closure() {
                 break;
             }
         }
-    })
+    });
+
+    trait MySpecialFnMut: FnOnce() {}
+    impl<T: FnOnce()> MySpecialFnMut for T {}
+    fn f4(_: impl MySpecialFnMut) {}
+    let mut it = 0..10;
+    f4(|| {
+        for x in it {
+            if x % 2 == 0 {
+                break;
+            }
+        }
+    });
 }
 
 fn main() {

tests/ui/while_let_on_iterator.rs

@@ -441,7 +441,19 @@ fn fn_once_closure() {
                 break;
             }
         }
-    })
+    });
+
+    trait MySpecialFnMut: FnOnce() {}
+    impl<T: FnOnce()> MySpecialFnMut for T {}
+    fn f4(_: impl MySpecialFnMut) {}
+    let mut it = 0..10;
+    f4(|| {
+        while let Some(x) = it.next() {
+            if x % 2 == 0 {
+                break;
+            }
+        }
+    });
 }
 
 fn main() {

tests/ui/while_let_on_iterator.stderr

@@ -131,7 +131,7 @@ error: this loop could be written as a `for` loop
   --> $DIR/while_let_on_iterator.rs:409:9
    |
 LL |         while let Some(x) = it.next() {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it.by_ref()`
 
 error: this loop could be written as a `for` loop
   --> $DIR/while_let_on_iterator.rs:419:9
@@ -152,10 +152,16 @@ LL |         while let Some(x) = it.next() {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_let_on_iterator.rs:449:5
+  --> $DIR/while_let_on_iterator.rs:451:9
+   |
+LL |         while let Some(x) = it.next() {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in it`
+
+error: this loop could be written as a `for` loop
+  --> $DIR/while_let_on_iterator.rs:461:5
    |
 LL |     while let Some(..) = it.next() {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in it`
 
-error: aborting due to 26 previous errors
+error: aborting due to 27 previous errors