From 8e0af8707a64d354500d13219d47e1cd4b0b6989 Mon Sep 17 00:00:00 2001
From: Jakub Mazurkiewicz <mazkuba3@gmail.com>
Date: Mon, 19 Sep 2022 15:28:34 +0200
Subject: [PATCH 1/2] Fix bug

---
 stl/inc/algorithm                                     |  4 ++--
 .../tests/P0896R4_ranges_alg_is_permutation/test.cpp  | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/stl/inc/algorithm b/stl/inc/algorithm
index 7805a59839..9603d16134 100644
--- a/stl/inc/algorithm
+++ b/stl/inc/algorithm
@@ -957,7 +957,7 @@ namespace ranges {
                 // We've trimmed matching prefixes and matching suffixes.
                 // Now we need to compare each range's prefix to the other range's suffix.
 
-                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) {
+                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) -> bool {
                     return _STD invoke(_Pred, _STD invoke(_Proj1, _STD forward<_Ty1>(_Left)),
                         _STD invoke(_Proj2, _STD forward<_Ty2>(_Right)));
                 };
@@ -1046,7 +1046,7 @@ namespace ranges {
                 // We've trimmed matching prefixes and matching suffixes.
                 // Now we need to compare each range's prefix to the other range's suffix.
 
-                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) {
+                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) -> bool {
                     return _STD invoke(_Pred, _STD invoke(_Proj1, _STD forward<_Ty1>(_Left)),
                         _STD invoke(_Proj2, _STD forward<_Ty2>(_Right)));
                 };
diff --git a/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp b/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
index ea364cdcad..214ab04a16 100644
--- a/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
@@ -134,6 +134,17 @@ struct instantiator {
             assert(ranges::is_permutation(
                 r1, r2, {}, [](int n) { return n + 1; }, [](int n) { return n - 1; }));
         }
+        { // Test GH-2888: `<algorithm>`: `ranges::is_permutation`'s helper lambda does not specify return type
+            struct NonCopyableBool {
+                constexpr operator bool() {
+                    return true;
+                };
+
+                NonCopyableBool()                       = default;
+                NonCopyableBool(const NonCopyableBool&) = delete;
+            } b;
+            assert(ranges::is_permutation(range2, range2, [&](auto, auto) -> NonCopyableBool& { return b; }));
+        }
     }
 };
 

From a4a4be4961a4c2731761634721a3eb95ed5ee9ff Mon Sep 17 00:00:00 2001
From: Casey Carter <cartec69@gmail.com>
Date: Tue, 20 Sep 2022 08:09:13 -0700
Subject: [PATCH 2/2] remove extraneous semicolon

---
 tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp b/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
index 214ab04a16..e633850055 100644
--- a/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
@@ -138,7 +138,7 @@ struct instantiator {
             struct NonCopyableBool {
                 constexpr operator bool() {
                     return true;
-                };
+                }
 
                 NonCopyableBool()                       = default;
                 NonCopyableBool(const NonCopyableBool&) = delete;