BLI_listbase: add utility macro for looping over lists with an index

Add to the 2.90 branch to avoid problems if fixes from master use it.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_listbase.h b/source/blender/blenlib/BLI_listbase.h
index fa7cf7a1847..932b63e43f7 100644
--- a/source/blender/blenlib/BLI_listbase.h
+++ b/source/blender/blenlib/BLI_listbase.h
@@ -186,6 +186,14 @@ struct LinkData *BLI_genericNodeN(void *data);
        ((var != NULL) ? ((void)(var##_iter_prev = (type)(((Link *)(var))->prev)), 1) : 0); \
        var = var##_iter_prev)
 
+/**
+ * A version of #LISTBASE_FOREACH that takes an index variable (declared outside this macro).
+ * This avoids possible accidents where using `continue` could miss incrementing the counter.
+ */
+#define LISTBASE_FOREACH_INDEX(type, var, list, index_var) \
+  for (type var = (((void)(index_var = 0)), (type)((list)->first)); var != NULL; \
+       var = (type)(((Link *)(var))->next), index_var++)
+
 #ifdef __cplusplus
 }
 #endif