Fix T61353: Crash converting a curve to a mesh

This was caused by curves pointing to each other
creating a cyclic dependency.

While the dependency graph detects this, generating a mesh for render
recursively generates data which cashes in this case.

Add in a check to detect cyclic links.

Note, this bug exists in 2.7x too - but only crashes on render
since 2.7x didn't use 'for_render' when converting data.

source/blender/blenkernel/BKE_curve.h

@@ -27,6 +27,7 @@ struct Curve;
 struct Depsgraph;
 struct EditNurb;
 struct GHash;
+struct LinkNode;
 struct ListBase;
 struct Main;
 struct Nurb;
@@ -119,7 +120,8 @@ void BKE_curve_bevelList_free(struct ListBase *bev);
 void BKE_curve_bevelList_make(struct Object *ob, struct ListBase *nurbs, bool for_render);
 void BKE_curve_bevel_make(
         struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob,  struct ListBase *disp,
-        const bool for_render, const bool use_render_resolution);
+        const bool for_render, const bool use_render_resolution,
+        struct LinkNode *ob_cyclic_list);
 
 void BKE_curve_forward_diff_bezier(float q0, float q1, float q2, float q3, float *p, int it, int stride);
 void BKE_curve_forward_diff_tangent_bezier(float q0, float q1, float q2, float q3, float *p, int it, int stride);

source/blender/blenkernel/BKE_displist.h

@@ -49,6 +49,7 @@ enum {
 /* prototypes */
 
 struct Depsgraph;
+struct LinkNode;
 struct ListBase;
 struct Main;
 struct Mesh;
@@ -83,12 +84,15 @@ void BKE_displist_make_surf(
         struct Mesh **r_final, const bool for_render, const bool for_orco, const bool use_render_resolution);
 void BKE_displist_make_curveTypes(
         struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob,
-        const bool for_render, const bool for_orco);
+        const bool for_render, const bool for_orco,
+        struct LinkNode *ob_cyclic_list);
 void BKE_displist_make_curveTypes_forRender(
         struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob, struct ListBase *dispbase,
-        struct Mesh **r_final, const bool for_orco, const bool use_render_resolution);
+        struct Mesh **r_final, const bool for_orco, const bool use_render_resolution,
+        struct LinkNode *ob_cyclic_list);
 void BKE_displist_make_curveTypes_forOrco(
-        struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob, struct ListBase *dispbase);
+        struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob, struct ListBase *dispbase,
+        struct LinkNode *ob_cyclic_list);
 void BKE_displist_make_mball(
         struct Depsgraph *depsgraph, struct Scene *scene, struct Object *ob);
 void BKE_displist_make_mball_forRender(

source/blender/blenkernel/intern/curve.c

@@ -31,6 +31,7 @@
 #include "BLI_math.h"
 #include "BLI_utildefines.h"
 #include "BLI_ghash.h"
+#include "BLI_linklist.h"
 
 #include "DNA_anim_types.h"
 #include "DNA_curve_types.h"
@@ -1735,7 +1736,7 @@ float *BKE_curve_make_orco(Depsgraph *depsgraph, Scene *scene, Object *ob, int *
 	float *fp, *coord_array;
 	ListBase disp = {NULL, NULL};
 
-	BKE_displist_make_curveTypes_forOrco(depsgraph, scene, ob, &disp);
+	BKE_displist_make_curveTypes_forOrco(depsgraph, scene, ob, &disp, NULL);
 
 	numVerts = 0;
 	for (dl = disp.first; dl; dl = dl->next) {
@@ -1828,7 +1829,8 @@ float *BKE_curve_make_orco(Depsgraph *depsgraph, Scene *scene, Object *ob, int *
 
 void BKE_curve_bevel_make(
         Depsgraph *depsgraph, Scene *scene, Object *ob, ListBase *disp,
-        const bool for_render, const bool use_render_resolution)
+        const bool for_render, const bool use_render_resolution,
+        LinkNode *ob_cyclic_list)
 {
 	DispList *dl, *dlnew;
 	Curve *bevcu, *cu;
@@ -1852,8 +1854,15 @@ void BKE_curve_bevel_make(
 			facy = cu->bevobj->size[1];
 
 			if (for_render) {
-				BKE_displist_make_curveTypes_forRender(depsgraph, scene, cu->bevobj, &bevdisp, NULL, false, use_render_resolution);
-				dl = bevdisp.first;
+				if (BLI_linklist_index(ob_cyclic_list, cu->bevobj) == -1) {
+					BKE_displist_make_curveTypes_forRender(
+					        depsgraph, scene, cu->bevobj, &bevdisp, NULL, false, use_render_resolution,
+					        &(LinkNode){ .link = ob, .next = ob_cyclic_list, });
+					dl = bevdisp.first;
+				}
+				else {
+					dl = NULL;
+				}
 			}
 			else if (cu->bevobj->runtime.curve_cache) {
 				dl = cu->bevobj->runtime.curve_cache->disp.first;

source/blender/blenkernel/intern/displist.c

@@ -38,6 +38,7 @@
 #include "BLI_math.h"
 #include "BLI_scanfill.h"
 #include "BLI_utildefines.h"
+#include "BLI_linklist.h"
 
 #include "BKE_displist.h"
 #include "BKE_cdderivedmesh.h"
@@ -683,7 +684,7 @@ static float displist_calc_taper(Depsgraph *depsgraph, Scene *scene, Object *tap
 
 	dl = taperobj->runtime.curve_cache ? taperobj->runtime.curve_cache->disp.first : NULL;
 	if (dl == NULL) {
-		BKE_displist_make_curveTypes(depsgraph, scene, taperobj, false, false);
+		BKE_displist_make_curveTypes(depsgraph, scene, taperobj, false, false, NULL);
 		dl = taperobj->runtime.curve_cache->disp.first;
 	}
 	if (dl) {
@@ -1554,8 +1555,9 @@ static void calc_bevfac_mapping(Curve *cu, BevList *bl, Nurb *nu,
 
 static void do_makeDispListCurveTypes(
         Depsgraph *depsgraph, Scene *scene, Object *ob, ListBase *dispbase,
-        Mesh **r_final,
-        const bool for_render, const bool for_orco, const bool use_render_resolution)
+        const bool for_render, const bool for_orco, const bool use_render_resolution,
+        LinkNode *ob_cyclic_list,
+        Mesh **r_final)
 {
 	Curve *cu = ob->data;
 
@@ -1593,7 +1595,9 @@ static void do_makeDispListCurveTypes(
 		BKE_curve_bevelList_make(ob, &nubase, use_render_resolution);
 
 		/* If curve has no bevel will return nothing */
-		BKE_curve_bevel_make(depsgraph, scene, ob, &dlbev, for_render, use_render_resolution);
+		BKE_curve_bevel_make(
+		        depsgraph, scene, ob, &dlbev, for_render, use_render_resolution,
+		        ob_cyclic_list);
 
 		/* no bevel or extrude, and no width correction? */
 		if (!dlbev.first && cu->width == 1.0f) {
@@ -1801,7 +1805,8 @@ static void do_makeDispListCurveTypes(
 }
 
 void BKE_displist_make_curveTypes(
-        Depsgraph *depsgraph, Scene *scene, Object *ob, const bool for_render, const bool for_orco)
+        Depsgraph *depsgraph, Scene *scene, Object *ob, const bool for_render, const bool for_orco,
+        LinkNode *ob_cyclic_list)
 {
 	ListBase *dispbase;
 
@@ -1819,7 +1824,10 @@ void BKE_displist_make_curveTypes(
 
 	dispbase = &(ob->runtime.curve_cache->disp);
 
-	do_makeDispListCurveTypes(depsgraph, scene, ob, dispbase, &ob->runtime.mesh_eval, for_render, for_orco, false);
+	do_makeDispListCurveTypes(
+	        depsgraph, scene, ob, dispbase, for_render, for_orco, false,
+	        ob_cyclic_list,
+	        &ob->runtime.mesh_eval);
 
 	boundbox_displist_object(ob);
 }
@@ -1827,23 +1835,31 @@ void BKE_displist_make_curveTypes(
 void BKE_displist_make_curveTypes_forRender(
         Depsgraph *depsgraph, Scene *scene, Object *ob, ListBase *dispbase,
         Mesh **r_final, const bool for_orco,
-        const bool use_render_resolution)
+        const bool use_render_resolution,
+        LinkNode *ob_cyclic_list)
 {
 	if (ob->runtime.curve_cache == NULL) {
 		ob->runtime.curve_cache = MEM_callocN(sizeof(CurveCache), "CurveCache for Curve");
 	}
 
-	do_makeDispListCurveTypes(depsgraph, scene, ob, dispbase, r_final, true, for_orco, use_render_resolution);
+	do_makeDispListCurveTypes(
+	        depsgraph, scene, ob, dispbase, true, for_orco, use_render_resolution,
+	        ob_cyclic_list,
+	        r_final);
 }
 
 void BKE_displist_make_curveTypes_forOrco(
-        Depsgraph *depsgraph, Scene *scene, Object *ob, ListBase *dispbase)
+        Depsgraph *depsgraph, Scene *scene, Object *ob, ListBase *dispbase,
+        LinkNode *ob_cyclic_list)
 {
 	if (ob->runtime.curve_cache == NULL) {
 		ob->runtime.curve_cache = MEM_callocN(sizeof(CurveCache), "CurveCache for Curve");
 	}
 
-	do_makeDispListCurveTypes(depsgraph, scene, ob, dispbase, NULL, 1, 1, 1);
+	do_makeDispListCurveTypes(
+	        depsgraph, scene, ob, dispbase, 1, 1, 1,
+	        ob_cyclic_list,
+	        NULL);
 }
 
 void BKE_displist_minmax(ListBase *dispbase, float min[3], float max[3])

source/blender/blenkernel/intern/effect.c

@@ -158,7 +158,7 @@ static void precalculate_effector(struct Depsgraph *depsgraph, EffectorCache *ef
 		Curve *cu = eff->ob->data;
 		if (cu->flag & CU_PATH) {
 			if (eff->ob->runtime.curve_cache == NULL || eff->ob->runtime.curve_cache->path == NULL || eff->ob->runtime.curve_cache->path->data == NULL)
-				BKE_displist_make_curveTypes(depsgraph, eff->scene, eff->ob, false, false);
+				BKE_displist_make_curveTypes(depsgraph, eff->scene, eff->ob, false, false, NULL);
 
 			if (eff->ob->runtime.curve_cache->path && eff->ob->runtime.curve_cache->path->data) {
 				where_on_path(eff->ob, 0.0, eff->guide_loc, eff->guide_dir, NULL, &eff->guide_radius, NULL);

source/blender/blenkernel/intern/mesh_convert.c

@@ -896,7 +896,9 @@ Mesh *BKE_mesh_new_from_object(
 			copycu->editnurb = tmpcu->editnurb;
 
 			/* get updated display list, and convert to a mesh */
-			BKE_displist_make_curveTypes_forRender(depsgraph, sce, tmpobj, &dispbase, &me_eval_final, false, render);
+			BKE_displist_make_curveTypes_forRender(
+			        depsgraph, sce, tmpobj, &dispbase, &me_eval_final, false, render,
+			        NULL);
 
 			copycu->editfont = NULL;
 			copycu->editnurb = NULL;

source/blender/blenkernel/intern/object_update.c

@@ -202,7 +202,7 @@ void BKE_object_handle_data_update(
 		case OB_CURVE:
 		case OB_SURF:
 		case OB_FONT:
-			BKE_displist_make_curveTypes(depsgraph, scene, ob, false, false);
+			BKE_displist_make_curveTypes(depsgraph, scene, ob, false, false, NULL);
 			break;
 
 		case OB_LATTICE:

source/blender/editors/curve/editcurve.c

@@ -6660,7 +6660,7 @@ static int match_texture_space_exec(bContext *C, wmOperator *UNUSED(op))
 	int a;
 
 	if (object->runtime.curve_cache == NULL) {
-		BKE_displist_make_curveTypes(depsgraph, scene, object, false, false);
+		BKE_displist_make_curveTypes(depsgraph, scene, object, false, false, NULL);
 	}
 
 	INIT_MINMAX(min, max);

source/blender/editors/object/object_add.c

@@ -1771,7 +1771,7 @@ static void convert_ensure_curve_cache(Depsgraph *depsgraph, Scene *scene, Objec
 		if (ELEM(ob->type, OB_SURF, OB_CURVE, OB_FONT)) {
 			/* We need 'for render' ON here, to enable computing bevel dipslist if needed.
 			 * Also makes sense anyway, we would not want e.g. to loose hidden parts etc. */
-			BKE_displist_make_curveTypes(depsgraph, scene, ob, true, false);
+			BKE_displist_make_curveTypes(depsgraph, scene, ob, true, false, NULL);
 		}
 		else if (ob->type == OB_MBALL) {
 			BKE_displist_make_mball(depsgraph, scene, ob);

source/blender/editors/object/object_modifier.c

@@ -105,7 +105,7 @@ static void object_force_modifier_update_for_bind(Depsgraph *depsgraph, Scene *s
 		BKE_displist_make_mball(depsgraph, scene, ob);
 	}
 	else if (ELEM(ob->type, OB_CURVE, OB_SURF, OB_FONT)) {
-		BKE_displist_make_curveTypes(depsgraph, scene, ob, false, false);
+		BKE_displist_make_curveTypes(depsgraph, scene, ob, false, false, NULL);
 	}
 }
 

source/blender/editors/object/object_relations.c

@@ -628,7 +628,7 @@ bool ED_object_parent_set(ReportList *reports, const bContext *C, Scene *scene,
 			if ((cu->flag & CU_PATH) == 0) {
 				cu->flag |= CU_PATH | CU_FOLLOW;
 				/* force creation of path data */
-				BKE_displist_make_curveTypes(depsgraph, scene, par, false, false);
+				BKE_displist_make_curveTypes(depsgraph, scene, par, false, false, NULL);
 			}
 			else {
 				cu->flag |= CU_FOLLOW;