rts: Fix use of sized array in Heap.h

Sized arrays cannot be used in headers that might be imported from C++.

Fixes #20199.

1 files changed, 6 insertions, 2 deletions

diff --git a/includes/rts/storage/Heap.h b/includes/rts/storage/Heap.h
index b950df76e5..b3b1efaf9f 100644
--- a/includes/rts/storage/Heap.h
+++ b/includes/rts/storage/Heap.h
@@ -18,10 +18,14 @@ void heap_view_closure_ptrs_in_pap_payload(StgClosure *ptrs[], StgWord *nptrs
 StgWord heap_view_closureSize(StgClosure *closure);
 
 /*
- * Collect the pointers of a closure into the given array. `size` should be
+ * Collect the pointers of a closure into the given array. The given array should be
  * large enough to hold all collected pointers e.g.
  * `heap_view_closureSize(closure)`. Returns the number of pointers collected.
  * The caller must ensure that `closure` is not modified (or moved by the GC)
  * for the duration of the call to `collect_pointers`.
+ *
+ * In principle this is
+ *   StgWord collect_pointers(StgClosure *closure, StgWord size, StgClosure *ptrs[size]);
+ * but we cannot write this and retain C++ compatibility.
  */
-StgWord collect_pointers(StgClosure *closure, StgWord size, StgClosure *ptrs[size]);
+StgWord collect_pointers(StgClosure *closure, StgClosure *ptrs[]);