RcppCore · kevinushey · Aug 26, 2026 · Aug 26, 2026
diff --git a/NEWS.md b/NEWS.md
@@ -1,5 +1,11 @@
 # RcppParallel (development version)
 
+* Fixed bundled oneTBB builds with recent libc++, which no longer includes
+  `<algorithm>` transitively. `tbb/concurrent_queue.h` uses `std::equal` but
+  did not include it, giving "no member named 'equal' in namespace 'std'" when
+  compiling `concurrent_bounded_queue.cpp`, as seen on CRAN's clang-trunk
+  checks. (#280)
+
 * Fixed bundled oneTBB builds and downstream compilation with Clang and libc++
   when targeting macOS 10.12 or earlier, where C++17 aligned allocation is not
   available. (#219)

diff --git a/patches/missing_algorithm_include.diff b/patches/missing_algorithm_include.diff
@@ -0,0 +1,26 @@
+Include <algorithm> in concurrent_queue.h, which uses std::equal in the
+operator== of both concurrent_queue and concurrent_bounded_queue but relies on
+some other header dragging <algorithm> in.
+
+libc++ trunk (as used by CRAN's clang-trunk / clang 23 checks) no longer
+provides that transitive include, so building the bundled oneTBB fails with
+'no member named equal in namespace std' when compiling
+src/tbb/concurrent_bounded_queue.cpp. Sibling containers -- concurrent_vector.h,
+concurrent_lru_cache.h -- already include <algorithm> explicitly; this brings
+concurrent_queue.h in line.
+
+Not yet fixed upstream as of oneTBB master; drop this once it is.
+
+diff --git a/src/tbb/include/oneapi/tbb/concurrent_queue.h b/src/tbb/include/oneapi/tbb/concurrent_queue.h
+index 9d7ec9a2..dd2ff34c 100644
+--- a/src/tbb/include/oneapi/tbb/concurrent_queue.h
++++ b/src/tbb/include/oneapi/tbb/concurrent_queue.h
+@@ -24,6 +24,8 @@
+ #include "detail/_containers_helpers.h"
+ #include "cache_aligned_allocator.h"
+
++#include <algorithm> // std::equal
++
+ namespace tbb {
+ namespace detail {
+ namespace d2 {
diff --git a/src/tbb/include/oneapi/tbb/concurrent_queue.h b/src/tbb/include/oneapi/tbb/concurrent_queue.h
@@ -24,6 +24,8 @@
 #include "detail/_containers_helpers.h"
 #include "cache_aligned_allocator.h"
 
+#include <algorithm> // std::equal
+
 namespace tbb {
 namespace detail {
 namespace d2 {