Define RAFT_WEAK_FUNCTION

cpp/include/raft/core/detail/macros.hpp

@@ -60,6 +60,20 @@
 #define RAFT_INLINE_CONDITIONAL inline
 #endif  // RAFT_COMPILED
 
+// The RAFT_WEAK_FUNCTION specificies that:
+//
+// 1. A function may be defined in multiple translation units (like inline)
+//
+// 2. Must still emit an external symbol (unlike inline). This enables declaring
+// a function signature in an `-ext` header and defining it in a source file.
+//
+// From
+// https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes:
+//
+// "The weak attribute causes a declaration of an external symbol to be emitted
+// as a weak symbol rather than a global."
+#define RAFT_WEAK_FUNCTION __attribute__((weak))
+
 /**
  * Some macro magic to remove optional parentheses of a macro argument.
  * See https://stackoverflow.com/a/62984543

cpp/include/raft/neighbors/detail/ivf_pq_compute_similarity-ext.cuh

@@ -17,6 +17,7 @@
 #pragma once
 
 #include <cuda_fp16.h>                               // __half
+#include <raft/core/detail/macros.hpp>               // RAFT_WEAK_FUNCTION
 #include <raft/distance/distance_types.hpp>          // raft::distance::DistanceType
 #include <raft/neighbors/detail/ivf_pq_fp_8bit.cuh>  // raft::neighbors::ivf_pq::detail::fp_8bit
 #include <raft/neighbors/ivf_pq_types.hpp>           // raft::neighbors::ivf_pq::codebook_gen
@@ -30,7 +31,8 @@ namespace raft::neighbors::ivf_pq::detail {
 // is_local_topk_feasible is not inline here, because we would have to define it
 // here as well. That would run the risk of the definitions here and in the
 // -inl.cuh header diverging.
-auto is_local_topk_feasible(uint32_t k, uint32_t n_probes, uint32_t n_queries) -> bool;
+auto RAFT_WEAK_FUNCTION is_local_topk_feasible(uint32_t k, uint32_t n_probes, uint32_t n_queries)
+  -> bool;
 
 template <typename OutT,
           typename LutT,

cpp/include/raft/neighbors/detail/ivf_pq_compute_similarity-inl.cuh

@@ -39,7 +39,7 @@ static_assert((kMaxCapacity >= 32) && !(kMaxCapacity & (kMaxCapacity - 1)),
               "kMaxCapacity must be a power of two, not smaller than the WarpSize.");
 
 // using weak attribute here, because it may be compiled multiple times.
-auto __attribute__((weak)) is_local_topk_feasible(uint32_t k, uint32_t n_probes, uint32_t n_queries)
+auto RAFT_WEAK_FUNCTION is_local_topk_feasible(uint32_t k, uint32_t n_probes, uint32_t n_queries)
   -> bool
 {
   if (k > kMaxCapacity) { return false; }             // warp_sort not possible