From 71ba2cf1e5e2eb75824b993cf389f27701f2dd2a Mon Sep 17 00:00:00 2001
From: Samuel Tardieu <sam@rfc1149.net>
Date: Wed, 22 Jan 2025 13:03:30 +0100
Subject: [PATCH] Extract `leaks_droppable_temporary_with_limited_lifetime()`

---
 clippy_lints/src/returns.rs | 25 ++++++-------------------
 clippy_utils/src/lib.rs     | 23 ++++++++++++++++++++---
 2 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/clippy_lints/src/returns.rs b/clippy_lints/src/returns.rs
index dfaee8cc3054..664e984fece3 100644
--- a/clippy_lints/src/returns.rs
+++ b/clippy_lints/src/returns.rs
@@ -1,10 +1,11 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
 use clippy_utils::source::{SpanRangeExt, snippet_with_context};
 use clippy_utils::sugg::has_enclosing_paren;
-use clippy_utils::visitors::{Descend, for_each_expr, for_each_unconsumed_temporary};
+use clippy_utils::visitors::{Descend, for_each_expr};
 use clippy_utils::{
-    binary_expr_needs_parentheses, fn_def_id, is_from_proc_macro, is_inside_let_else, is_res_lang_ctor, path_res,
-    path_to_local_id, span_contains_cfg, span_find_starting_semi,
+    binary_expr_needs_parentheses, fn_def_id, is_from_proc_macro, is_inside_let_else, is_res_lang_ctor,
+    leaks_droppable_temporary_with_limited_lifetime, path_res, path_to_local_id, span_contains_cfg,
+    span_find_starting_semi,
 };
 use core::ops::ControlFlow;
 use rustc_ast::MetaItemInner;
@@ -389,22 +390,8 @@ fn check_final_expr<'tcx>(
                 }
             };
 
-            if let Some(inner) = inner {
-                if for_each_unconsumed_temporary(cx, inner, |temporary_ty| {
-                    if temporary_ty.has_significant_drop(cx.tcx, cx.typing_env())
-                        && temporary_ty
-                            .walk()
-                            .any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(re) if !re.is_static()))
-                    {
-                        ControlFlow::Break(())
-                    } else {
-                        ControlFlow::Continue(())
-                    }
-                })
-                .is_break()
-                {
-                    return;
-                }
+            if inner.is_some_and(|inner| leaks_droppable_temporary_with_limited_lifetime(cx, inner)) {
+                return;
             }
 
             if ret_span.from_expansion() || is_from_proc_macro(cx, expr) {
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index 8b39e2aa4e25..6869078ba0ad 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -117,15 +117,15 @@ use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
-    self as rustc_ty, Binder, BorrowKind, ClosureKind, EarlyBinder, FloatTy, GenericArgsRef, IntTy, Ty, TyCtxt,
-    TypeVisitableExt, UintTy, UpvarCapture,
+    self as rustc_ty, Binder, BorrowKind, ClosureKind, EarlyBinder, FloatTy, GenericArgKind, GenericArgsRef, IntTy, Ty,
+    TyCtxt, TypeVisitableExt, UintTy, UpvarCapture,
 };
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{Ident, Symbol, kw};
 use rustc_span::{InnerSpan, Span, sym};
 use rustc_target::abi::Integer;
-use visitors::Visitable;
+use visitors::{Visitable, for_each_unconsumed_temporary};
 
 use crate::consts::{ConstEvalCtxt, Constant, mir_to_const};
 use crate::higher::Range;
@@ -3465,3 +3465,20 @@ pub fn is_receiver_of_method_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool
     }
     false
 }
+
+/// Returns true if `expr` creates any temporary whose type references a non-static lifetime and has
+/// a significant drop and does not consume it.
+pub fn leaks_droppable_temporary_with_limited_lifetime<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
+    for_each_unconsumed_temporary(cx, expr, |temporary_ty| {
+        if temporary_ty.has_significant_drop(cx.tcx, cx.typing_env())
+            && temporary_ty
+                .walk()
+                .any(|arg| matches!(arg.unpack(), GenericArgKind::Lifetime(re) if !re.is_static()))
+        {
+            ControlFlow::Break(())
+        } else {
+            ControlFlow::Continue(())
+        }
+    })
+    .is_break()
+}