BLI_string_utils: BLI_uniquename no longer accepts NULL defname

A NULL defname would early exit (doing nothing) this isn't good behavior
as this function should always make the name unique and a NULL defname
is likely an error in the code which would allow duplicate names.
This is also inconsistent with BLI_uniquename_cb which always
wrote the defname into the name if it was empty.

Mark this argument as never-NULL.

source/blender/blenkernel/BKE_asset.h

@@ -42,7 +42,8 @@ struct AssetTagEnsureResult {
   bool is_new;
 };
 
-struct AssetTag *BKE_asset_metadata_tag_add(struct AssetMetaData *asset_data, const char *name);
+struct AssetTag *BKE_asset_metadata_tag_add(struct AssetMetaData *asset_data, const char *name)
+    ATTR_NONNULL(1, 2);
 /**
  * Make sure there is a tag with name \a name, create one if needed.
  */

source/blender/blenkernel/BKE_particle.h

@@ -9,6 +9,7 @@
  */
 
 #include "BLI_buffer.h"
+#include "BLI_compiler_attrs.h"
 #include "BLI_utildefines.h"
 
 #include "DNA_particle_types.h"
@@ -376,7 +377,8 @@ void psys_reset(struct ParticleSystem *psys, int mode);
 
 void psys_find_parents(struct ParticleSimulationData *sim, bool use_render_params);
 
-void psys_unique_name(struct Object *object, struct ParticleSystem *psys, const char *defname);
+void psys_unique_name(struct Object *object, struct ParticleSystem *psys, const char *defname)
+    ATTR_NONNULL(1, 2, 3);
 
 /**
  * Calculates paths ready for drawing/rendering

source/blender/blenkernel/intern/attribute.cc

@@ -265,7 +265,8 @@ bool BKE_id_attribute_calc_unique_name(ID *id, const char *name, char *outname)
     BLI_strncpy_utf8(outname, name, maxlength);
   }
 
-  return BLI_uniquename_cb(unique_name_cb, &data, nullptr, '.', outname, maxlength);
+  const char *defname = ""; /* Dummy argument, never used as `name` is never zero length. */
+  return BLI_uniquename_cb(unique_name_cb, &data, defname, '.', outname, maxlength);
 }
 
 CustomDataLayer *BKE_id_attribute_new(ID *id,

source/blender/blenkernel/intern/customdata.cc

@@ -4416,7 +4416,8 @@ void CustomData_set_layer_unique_name(CustomData *data, const int index)
     STRNCPY(nlayer->name, DATA_(typeInfo->defaultname));
   }
 
-  BLI_uniquename_cb(customdata_unique_check, &data_arg, nullptr, '.', nlayer->name, max_length);
+  const char *defname = ""; /* Dummy argument, never used as `name` is never zero length. */
+  BLI_uniquename_cb(customdata_unique_check, &data_arg, defname, '.', nlayer->name, max_length);
 }
 
 void CustomData_validate_layer_name(const CustomData *data,

source/blender/blenlib/BLI_string_utils.h

@@ -112,7 +112,7 @@ bool BLI_uniquename(struct ListBase *list,
                     const char *defname,
                     char delim,
                     int name_offset,
-                    size_t name_len) ATTR_NONNULL(1);
+                    size_t name_len) ATTR_NONNULL(1, 3);
 
 /* Expand array functions. */
 

source/blender/blenlib/intern/string_utils.c

@@ -321,7 +321,7 @@ bool BLI_uniquename(
   BLI_assert(name_len > 1);
 
   /* See if we are given an empty string */
-  if (ELEM(NULL, vlink, defname)) {
+  if (ELEM(NULL, vlink)) {
     return false;
   }