[libcxx-commits] [libcxx] 47405ba - [libc++] fix incorrect definition of __indirectly_binary_right_foldable (#219957)

[via libcxx-commits]

Author: Connector Switch
Date: 2026-08-31T23:03:03+08:00
New Revision: 47405bae765c9ac34cd91636a31d5fb5212b49e3

URL: https://github.com/llvm/llvm-project/commit/47405bae765c9ac34cd91636a31d5fb5212b49e3
DIFF: https://github.com/llvm/llvm-project/commit/47405bae765c9ac34cd91636a31d5fb5212b49e3.diff

LOG: [libc++] fix incorrect definition of __indirectly_binary_right_foldable (#219957)

Fixes https://github.com/llvm/llvm-project/issues/219618.

Added: 
    

Modified: 
    libcxx/include/__algorithm/ranges_fold.h
    libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_left.pass.cpp
    libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_right.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__algorithm/ranges_fold.h b/libcxx/include/__algorithm/ranges_fold.h
index 27e042395dad0..286d7c436412f 100644
--- a/libcxx/include/__algorithm/ranges_fold.h
+++ b/libcxx/include/__algorithm/ranges_fold.h
@@ -96,11 +96,7 @@ struct __flipped {
 };
 
 template <class _Func, class _Tp, class _Iter>
-concept __indirectly_binary_right_foldable =
-    __indirectly_binary_left_foldable_impl<__flipped<_Func>,
-                                           _Tp,
-                                           _Iter,
-                                           invoke_result_t<_Func&, _Tp, iter_reference_t<_Iter>>>;
+concept __indirectly_binary_right_foldable = __indirectly_binary_left_foldable<__flipped<_Func>, _Tp, _Iter>;
 
 struct __fold_left_with_iter {
   template <input_iterator _Ip, sentinel_for<_Ip> _Sp, class _Tp, __indirectly_binary_left_foldable<_Tp, _Ip> _Fp>

diff  --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_left.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_left.pass.cpp
index e08d54c597853..d9a325a83872b 100644
--- a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_left.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_left.pass.cpp
@@ -330,6 +330,12 @@ void runtime_only_test_case() {
     auto const expected = triangular_sum(data);
     check(data, 0, std::plus<long>(), static_cast<long>(expected));
   }
+
+  {
+    auto const data = std::vector<int>{1, 2, 3, 4};
+    auto concat     = [](std::string s, int x) { return s + ':' + std::to_string(x); };
+    check(data, "A", concat, std::string{"A:1:2:3:4"});
+  }
 }
 
 int main(int, char**) {

diff  --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_right.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_right.pass.cpp
index 26437884c55b6..51a10864d0734 100644
--- a/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_right.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.fold/ranges.fold_right.pass.cpp
@@ -186,6 +186,12 @@ void runtime_only_test_case() {
     auto const expected = triangular_sum(data);
     check(data, 0, std::plus<long>(), static_cast<long>(expected));
   }
+
+  {
+    auto const data = std::vector<int>{1, 2, 3, 4};
+    auto concat     = [](int x, std::string s) { return s + ':' + std::to_string(x); };
+    check(data, "A", concat, std::string{"A:4:3:2:1"});
+  }
 }
 
 int main(int, char**) {