Fix T67999: calling Mesh.materials.clear() crashes Blender

The `BKE_material_pop_id()` and `BKE_material_clear_id()` functions had
a parameter `update_data` that, when `false`, would cause the mesh polys
to keep their material index, even when the indexed material slots were
removed. This behaviour was never used in the C code and not supported
by the drawing code, making polygons disappear and causing crashes. The
Python binding in RNA, however, defaulted to `update_data=False`.

This commit removes the `update_data` parameter altogether, and makes
the functions always fix up the material indices.

Reviewed by: mont29, brecht

4 files changed, 13 insertions, 25 deletions

diff --git a/source/blender/blenkernel/BKE_material.h b/source/blender/blenkernel/BKE_material.h
index 5bb69c7166e..44a8f98e994 100644
--- a/source/blender/blenkernel/BKE_material.h
+++ b/source/blender/blenkernel/BKE_material.h
@@ -104,9 +104,8 @@ void BKE_material_append_id(struct Main *bmain, struct ID *id, struct Material *
 struct Material *BKE_material_pop_id(struct Main *bmain,
                                      struct ID *id,
                                      /* index is an int because of RNA. */
-                                     int index,
-                                     bool update_data);
-void BKE_material_clear_id(struct Main *bmain, struct ID *id, bool update_data);
+                                     int index);
+void BKE_material_clear_id(struct Main *bmain, struct ID *id);
 /* rendering */
 
 void ramp_blend(int type, float r_col[3], const float fac, const float col[3]);
diff --git a/source/blender/blenkernel/intern/material.c b/source/blender/blenkernel/intern/material.c
index b01c1189fd1..1545ae4f48f 100644
--- a/source/blender/blenkernel/intern/material.c
+++ b/source/blender/blenkernel/intern/material.c
@@ -461,7 +461,7 @@ void BKE_material_append_id(Main *bmain, ID *id, Material *ma)
   }
 }
 
-Material *BKE_material_pop_id(Main *bmain, ID *id, int index_i, bool update_data)
+Material *BKE_material_pop_id(Main *bmain, ID *id, int index_i)
 {
   short index = (short)index_i;
   Material *ret = NULL;
@@ -489,10 +489,7 @@ Material *BKE_material_pop_id(Main *bmain, ID *id, int index_i, bool update_data
         test_all_objects_materials(bmain, id);
       }
 
-      if (update_data) {
-        /* decrease mat_nr index */
-        material_data_index_remove_id(id, index);
-      }
+      material_data_index_remove_id(id, index);
 
       DEG_id_tag_update(id, ID_RECALC_COPY_ON_WRITE);
       DEG_relations_tag_update(bmain);
@@ -502,7 +499,7 @@ Material *BKE_material_pop_id(Main *bmain, ID *id, int index_i, bool update_data
   return ret;
 }
 
-void BKE_material_clear_id(Main *bmain, ID *id, bool update_data)
+void BKE_material_clear_id(Main *bmain, ID *id)
 {
   Material ***matar;
   if ((matar = give_matarar_id(id))) {
@@ -516,12 +513,9 @@ void BKE_material_clear_id(Main *bmain, ID *id, bool update_data)
       MEM_freeN(*matar);
       *matar = NULL;
     }
-    test_all_objects_materials(bmain, id);
 
-    if (update_data) {
-      /* decrease mat_nr index */
-      material_data_index_clear_id(id);
-    }
+    test_all_objects_materials(bmain, id);
+    material_data_index_clear_id(id);
 
     DEG_id_tag_update(id, ID_RECALC_COPY_ON_WRITE);
     DEG_relations_tag_update(bmain);
diff --git a/source/blender/editors/mesh/editmesh_tools.c b/source/blender/editors/mesh/editmesh_tools.c
index f57e8141f27..4e58fee61a2 100644
--- a/source/blender/editors/mesh/editmesh_tools.c
+++ b/source/blender/editors/mesh/editmesh_tools.c
@@ -4040,7 +4040,7 @@ static void mesh_separate_material_assign_mat_nr(Main *bmain, Object *ob, const
       ma_obdata = NULL;
     }
 
-    BKE_material_clear_id(bmain, obdata, true);
+    BKE_material_clear_id(bmain, obdata);
     BKE_material_resize_object(bmain, ob, 1, true);
     BKE_material_resize_id(bmain, obdata, 1, true);
 
@@ -4051,7 +4051,7 @@ static void mesh_separate_material_assign_mat_nr(Main *bmain, Object *ob, const
     id_us_plus((ID *)ma_obdata);
   }
   else {
-    BKE_material_clear_id(bmain, obdata, true);
+    BKE_material_clear_id(bmain, obdata);
     BKE_material_resize_object(bmain, ob, 0, true);
     BKE_material_resize_id(bmain, obdata, 0, true);
   }
diff --git a/source/blender/makesrna/intern/rna_ID.c b/source/blender/makesrna/intern/rna_ID.c
index 57cdbbadeb8..7996750a1b8 100644
--- a/source/blender/makesrna/intern/rna_ID.c
+++ b/source/blender/makesrna/intern/rna_ID.c
@@ -642,8 +642,7 @@ static void rna_IDMaterials_append_id(ID *id, Main *bmain, Material *ma)
   WM_main_add_notifier(NC_OBJECT | ND_OB_SHADING, id);
 }
 
-static Material *rna_IDMaterials_pop_id(
-    ID *id, Main *bmain, ReportList *reports, int index_i, bool remove_material_slot)
+static Material *rna_IDMaterials_pop_id(ID *id, Main *bmain, ReportList *reports, int index_i)
 {
   Material *ma;
   short *totcol = give_totcolp_id(id);
@@ -657,7 +656,7 @@ static Material *rna_IDMaterials_pop_id(
     return NULL;
   }
 
-  ma = BKE_material_pop_id(bmain, id, index_i, remove_material_slot);
+  ma = BKE_material_pop_id(bmain, id, index_i);
 
   if (*totcol == totcol_orig) {
     BKE_report(reports, RPT_ERROR, "No material to removed");
@@ -671,9 +670,9 @@ static Material *rna_IDMaterials_pop_id(
   return ma;
 }
 
-static void rna_IDMaterials_clear_id(ID *id, Main *bmain, bool remove_material_slot)
+static void rna_IDMaterials_clear_id(ID *id, Main *bmain)
 {
-  BKE_material_clear_id(bmain, id, remove_material_slot);
+  BKE_material_clear_id(bmain, id);
 
   DEG_id_tag_update(id, ID_RECALC_GEOMETRY);
   WM_main_add_notifier(NC_OBJECT | ND_DRAW, id);
@@ -1116,16 +1115,12 @@ static void rna_def_ID_materials(BlenderRNA *brna)
   RNA_def_function_ui_description(func, "Remove a material from the data-block");
   parm = RNA_def_int(
       func, "index", -1, -MAXMAT, MAXMAT, "", "Index of material to remove", 0, MAXMAT);
-  RNA_def_boolean(
-      func, "update_data", 0, "", "Update data by re-adjusting the material slots assigned");
   parm = RNA_def_pointer(func, "material", "Material", "", "Material to remove");
   RNA_def_function_return(func, parm);
 
   func = RNA_def_function(srna, "clear", "rna_IDMaterials_clear_id");
   RNA_def_function_flag(func, FUNC_USE_MAIN);
   RNA_def_function_ui_description(func, "Remove all materials from the data-block");
-  RNA_def_boolean(
-      func, "update_data", 0, "", "Update data by re-adjusting the material slots assigned");
 }
 
 static void rna_def_image_preview(BlenderRNA *brna)