From af35dcd33012c131bf2d3675bb40591b740c7728 Mon Sep 17 00:00:00 2001
From: apoisternex <santinoferrazzuolo@proton.me>
Date: Sat, 3 Aug 2024 21:24:51 -0300
Subject: [PATCH 1/2] Fix [`needless_return`] false negative when returned
 expression borrows a value

Fixes #12907

changelog: Fix [`needless_return`] false negative when returned expression borrows a value
---
 clippy_lints/src/returns.rs     | 22 ++++++++++++++++++----
 tests/ui/needless_return.fixed  |  4 ++++
 tests/ui/needless_return.rs     |  4 ++++
 tests/ui/needless_return.stderr | 14 +++++++++++++-
 4 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/clippy_lints/src/returns.rs b/clippy_lints/src/returns.rs
index 13016cdad..034c44a97 100644
--- a/clippy_lints/src/returns.rs
+++ b/clippy_lints/src/returns.rs
@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
 use clippy_utils::source::{snippet_opt, snippet_with_context};
 use clippy_utils::sugg::has_enclosing_paren;
-use clippy_utils::visitors::{for_each_expr, Descend};
+use clippy_utils::visitors::{for_each_expr, for_each_unconsumed_temporary, Descend};
 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,
@@ -384,10 +384,24 @@ fn check_final_expr<'tcx>(
                 }
             };
 
-            let borrows = inner.map_or(false, |inner| last_statement_borrows(cx, inner));
-            if borrows {
-                return;
+            if let Some(inner) = inner {
+                if for_each_unconsumed_temporary(cx, inner, |temporary_ty| {
+                    if temporary_ty.has_significant_drop(cx.tcx, cx.param_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 ret_span.from_expansion() {
                 return;
             }
diff --git a/tests/ui/needless_return.fixed b/tests/ui/needless_return.fixed
index fc4129e1d..c5c570690 100644
--- a/tests/ui/needless_return.fixed
+++ b/tests/ui/needless_return.fixed
@@ -355,4 +355,8 @@ fn conjunctive_blocks() -> String {
     ({ "a".to_string() } + "b" + { "c" })
 }
 
+fn issue12907() -> String {
+    "".split("").next().unwrap().to_string()
+}
+
 fn main() {}
diff --git a/tests/ui/needless_return.rs b/tests/ui/needless_return.rs
index 61c7a0200..738611391 100644
--- a/tests/ui/needless_return.rs
+++ b/tests/ui/needless_return.rs
@@ -365,4 +365,8 @@ fn conjunctive_blocks() -> String {
     return { "a".to_string() } + "b" + { "c" };
 }
 
+fn issue12907() -> String {
+    return "".split("").next().unwrap().to_string();
+}
+
 fn main() {}
diff --git a/tests/ui/needless_return.stderr b/tests/ui/needless_return.stderr
index ea9c230ea..da0fa220d 100644
--- a/tests/ui/needless_return.stderr
+++ b/tests/ui/needless_return.stderr
@@ -665,5 +665,17 @@ LL -     return { "a".to_string() } + "b" + { "c" };
 LL +     ({ "a".to_string() } + "b" + { "c" })
    |
 
-error: aborting due to 53 previous errors
+error: unneeded `return` statement
+  --> tests/ui/needless_return.rs:369:5
+   |
+LL |     return "".split("").next().unwrap().to_string();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove `return`
+   |
+LL -     return "".split("").next().unwrap().to_string();
+LL +     "".split("").next().unwrap().to_string()
+   |
+
+error: aborting due to 54 previous errors
 

From 66283bff5fde5f310f3dd373d22cd4f892b3d312 Mon Sep 17 00:00:00 2001
From: apoisternex <santinoferrazzuolo@proton.me>
Date: Sun, 4 Aug 2024 10:45:42 -0300
Subject: [PATCH 2/2] apply [`needless_return`] suggestion

---
 clippy_lints/src/useless_conversion.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/clippy_lints/src/useless_conversion.rs b/clippy_lints/src/useless_conversion.rs
index 2f7d54e73..1890b3fdd 100644
--- a/clippy_lints/src/useless_conversion.rs
+++ b/clippy_lints/src/useless_conversion.rs
@@ -217,12 +217,12 @@ impl<'tcx> LateLintPass<'tcx> for UselessConversion {
                             },
                             ExprKind::MethodCall(.., args, _) => {
                                 cx.typeck_results().type_dependent_def_id(parent.hir_id).map(|did| {
-                                    return (
+                                    (
                                         did,
                                         args,
                                         cx.typeck_results().node_args(parent.hir_id),
                                         MethodOrFunction::Method,
-                                    );
+                                    )
                                 })
                             },
                             _ => None,