unnecessary_to_owned: don't call iter() on a temporary object (#14243)

fix #14242

changelog: [`unnecessary_to_owned`]: don't call `iter` on a temporary
object

Author: Centri3

clippy_lints/src/casts/borrow_as_ptr.rs

@@ -2,11 +2,10 @@ use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::msrvs::Msrv;
 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
 use clippy_utils::sugg::has_enclosing_paren;
-use clippy_utils::{is_lint_allowed, msrvs, std_or_core};
+use clippy_utils::{is_expr_temporary_value, is_lint_allowed, msrvs, std_or_core};
 use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Ty, TyKind};
 use rustc_lint::LateContext;
-use rustc_middle::ty::adjustment::Adjust;
 use rustc_span::BytePos;
 
 use super::BORROW_AS_PTR;
@@ -25,12 +24,7 @@ pub(super) fn check<'tcx>(
         let mut app = Applicability::MachineApplicable;
         let snip = snippet_with_context(cx, e.span, cast_expr.span.ctxt(), "..", &mut app).0;
         // Fix #9884
-        if !e.is_place_expr(|base| {
-            cx.typeck_results()
-                .adjustments()
-                .get(base.hir_id)
-                .is_some_and(|x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
-        }) {
+        if is_expr_temporary_value(cx, e) {
             return false;
         }
 

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -6,7 +6,8 @@ use clippy_utils::source::{SpanRangeExt, snippet};
 use clippy_utils::ty::{get_iterator_item_ty, implements_trait, is_copy, is_type_diagnostic_item, is_type_lang_item};
 use clippy_utils::visitors::find_all_ret_expressions;
 use clippy_utils::{
-    fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item, peel_middle_ty_refs, return_ty,
+    fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item, is_expr_temporary_value, peel_middle_ty_refs,
+    return_ty,
 };
 use rustc_errors::Applicability;
 use rustc_hir::def::{DefKind, Res};
@@ -219,6 +220,8 @@ fn check_into_iter_call_arg(
         && let Some(receiver_snippet) = receiver.span.get_source_text(cx)
         // If the receiver is a `Cow`, we can't remove the `into_owned` generally, see https://github.com/rust-lang/rust-clippy/issues/13624.
         && !is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::Cow)
+        // Calling `iter()` on a temporary object can lead to false positives. #14242
+        && !is_expr_temporary_value(cx, receiver)
     {
         if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver, true) {
             return true;

clippy_utils/src/lib.rs

@@ -2331,6 +2331,18 @@ pub fn is_expr_final_block_expr(tcx: TyCtxt<'_>, expr: &Expr<'_>) -> bool {
     matches!(tcx.parent_hir_node(expr.hir_id), Node::Block(..))
 }
 
+/// Checks if the expression is a temporary value.
+// This logic is the same as the one used in rustc's `check_named_place_expr function`.
+// https://github.com/rust-lang/rust/blob/3ed2a10d173d6c2e0232776af338ca7d080b1cd4/compiler/rustc_hir_typeck/src/expr.rs#L482-L499
+pub fn is_expr_temporary_value(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    !expr.is_place_expr(|base| {
+        cx.typeck_results()
+            .adjustments()
+            .get(base.hir_id)
+            .is_some_and(|x| x.iter().any(|adj| matches!(adj.kind, Adjust::Deref(_))))
+    })
+}
+
 pub fn std_or_core(cx: &LateContext<'_>) -> Option<&'static str> {
     if !is_no_std_crate(cx) {
         Some("std")

tests/ui/unnecessary_to_owned.fixed

@@ -195,19 +195,11 @@ fn main() {
     //~^ unnecessary_to_owned
     let _ = slice.iter().copied();
     //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].iter().cloned();
-    //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].iter().cloned();
-    //~^ unnecessary_to_owned
 
     let _ = slice.iter().copied();
     //~^ unnecessary_to_owned
     let _ = slice.iter().copied();
     //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].iter().cloned();
-    //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].iter().cloned();
-    //~^ unnecessary_to_owned
 
     let _ = check_files(&[FileType::Account]);
 
@@ -317,19 +309,6 @@ fn get_file_path(_file_type: &FileType) -> Result<std::path::PathBuf, std::io::E
 
 fn require_string(_: &String) {}
 
-#[clippy::msrv = "1.35"]
-fn _msrv_1_35() {
-    // `copied` was stabilized in 1.36, so clippy should use `cloned`.
-    let _ = &["x"][..].iter().cloned();
-    //~^ unnecessary_to_owned
-}
-
-#[clippy::msrv = "1.36"]
-fn _msrv_1_36() {
-    let _ = &["x"][..].iter().copied();
-    //~^ unnecessary_to_owned
-}
-
 // https://github.com/rust-lang/rust-clippy/issues/8507
 mod issue_8507 {
     #![allow(dead_code)]
@@ -680,3 +659,18 @@ fn issue13624() -> impl IntoIterator {
 
     cow.into_owned().into_iter()
 }
+
+mod issue_14242 {
+    use std::rc::Rc;
+
+    #[derive(Copy, Clone)]
+    struct Foo;
+
+    fn rc_slice_provider() -> Rc<[Foo]> {
+        Rc::from([Foo])
+    }
+
+    fn iterator_provider() -> impl Iterator<Item = Foo> {
+        rc_slice_provider().to_vec().into_iter()
+    }
+}

tests/ui/unnecessary_to_owned.rs

@@ -195,19 +195,11 @@ fn main() {
     //~^ unnecessary_to_owned
     let _ = slice.to_owned().into_iter();
     //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].to_vec().into_iter();
-    //~^ unnecessary_to_owned
-    let _ = [std::path::PathBuf::new()][..].to_owned().into_iter();
-    //~^ unnecessary_to_owned
 
     let _ = IntoIterator::into_iter(slice.to_vec());
     //~^ unnecessary_to_owned
     let _ = IntoIterator::into_iter(slice.to_owned());
     //~^ unnecessary_to_owned
-    let _ = IntoIterator::into_iter([std::path::PathBuf::new()][..].to_vec());
-    //~^ unnecessary_to_owned
-    let _ = IntoIterator::into_iter([std::path::PathBuf::new()][..].to_owned());
-    //~^ unnecessary_to_owned
 
     let _ = check_files(&[FileType::Account]);
 
@@ -317,19 +309,6 @@ fn get_file_path(_file_type: &FileType) -> Result<std::path::PathBuf, std::io::E
 
 fn require_string(_: &String) {}
 
-#[clippy::msrv = "1.35"]
-fn _msrv_1_35() {
-    // `copied` was stabilized in 1.36, so clippy should use `cloned`.
-    let _ = &["x"][..].to_vec().into_iter();
-    //~^ unnecessary_to_owned
-}
-
-#[clippy::msrv = "1.36"]
-fn _msrv_1_36() {
-    let _ = &["x"][..].to_vec().into_iter();
-    //~^ unnecessary_to_owned
-}
-
 // https://github.com/rust-lang/rust-clippy/issues/8507
 mod issue_8507 {
     #![allow(dead_code)]
@@ -680,3 +659,18 @@ fn issue13624() -> impl IntoIterator {
 
     cow.into_owned().into_iter()
 }
+
+mod issue_14242 {
+    use std::rc::Rc;
+
+    #[derive(Copy, Clone)]
+    struct Foo;
+
+    fn rc_slice_provider() -> Rc<[Foo]> {
+        Rc::from([Foo])
+    }
+
+    fn iterator_provider() -> impl Iterator<Item = Foo> {
+        rc_slice_provider().to_vec().into_iter()
+    }
+}