Can not add or remove tags from inside a system.

[WEREMSOFT]

Describe the bug I'm trying to remove and add tags to entities in order to process them by different systems. The idea is using tags to implement a finite state machine, being the tags handled as states.

I tried to send the reference to the tag in two ways to the system: As a context and with the nothing operator. But the program crash with this stack trace:

 ecs_vector_count
 ecs_type_merge
 ecs_merge_entity
 ecs_merge_commits
 ecs_stage_merge
 ecs_merge
 run_single_thread_stage
 ecs_process
 main.c

To Reproduce Run the code and try to change the systems where the objects are being processed to the other system.

#include <stdio.h>
#include <flecs.h>

void system_evens(ecs_rows_t *rows){
    printf("evens\n");
    ecs_entity_t my_tag = ecs_get_system_context(rows->world, rows->system);
    ECS_COLUMN_ENTITY(rows, tag_to_remove, 1);
    ECS_COLUMN_ENTITY(rows, tag_to_add, 2);
    for(int i = 0; i < rows->count; i++){
        _ecs_remove(rows->world, rows->entities[i], tag_to_remove);
        // the following line doesn't work: Exception: EXC_BAD_ACCESS (code=1, address=0xf)
//        _ecs_add(rows->world, rows->entities[i], tag_to_add);
    }
}

void system_odds(ecs_rows_t *rows){
    printf("ods\n");
    ECS_COLUMN_ENTITY(rows, tag_to_remove, 1);
    ECS_COLUMN_ENTITY(rows, tag_to_add, 2);
    for(int i = 0; i < rows->count; i++){
        _ecs_add(rows->world, rows->entities[i], tag_to_add);
        _ecs_remove(rows->world, rows->entities[i], tag_to_remove);
    }
}

void system_test_update(ecs_rows_t *rows) {
    printf("updating\n");
}

int main(int argc, char *argv[]) {
    ecs_world_t *world = ecs_init_w_args(argc, argv);
    ECS_TAG(world, tag_evens);
    ECS_TAG(world, tag_odds);
    ECS_SYSTEM(world, system_test_update, EcsOnUpdate, 0);

    ECS_SYSTEM(world, system_evens, EcsOnUpdate, tag_evens, .tag_odds);
    ecs_set_system_context(world, system_evens, tag_odds);

    ECS_SYSTEM(world, system_odds, EcsOnUpdate, tag_odds, .tag_evens);
    ecs_set_system_context(world, system_odds, tag_evens);

    int break_condition = 100;

    ECS_TYPE(world, Dummy, tag_evens);
    ecs_new_w_count(world, Dummy, 1);

    // The system crash here: Exception: EXC_BAD_ACCESS (code=1, address=0xe)
    // Stack Trace:
    /*
     ecs_vector_count
     ecs_type_merge
     ecs_merge_entity
     ecs_merge_commits
     ecs_stage_merge
     ecs_merge
     run_single_thread_stage
     ecs_process
     main.c
     */
    while(ecs_progress(world, 0) && break_condition--);

    ecs_fini(world);
}

Expected behavior The program should print "Even" and "Odd" while the systems have entities to process.

Actual Behavior The program crash.

Aditional Context You can see the full code in the following github https://github.com/WEREMSOFT/FlecsTests/blob/merge_systems/src/main.c

[WEREMSOFT]

I was doing it wrong. This code is the correct one:

#include <stdio.h>
#include <flecs.h>

void system_evens(ecs_rows_t *rows) {
    printf("evens\n");
    ECS_COLUMN_COMPONENT(rows, tag_to_remove, 1);
    ECS_COLUMN_COMPONENT(rows, tag_to_add, 2);
    for (int i = 0; i < rows->count; i++) {
        ecs_remove(rows->world, rows->entities[i], tag_to_remove);
        ecs_add(rows->world, rows->entities[i], tag_to_add);
    }
}

void system_odds(ecs_rows_t *rows) {
    printf("ods\n");
    ECS_COLUMN_COMPONENT(rows, tag_to_remove, 1);
    ECS_COLUMN_COMPONENT(rows, tag_to_add, 2);
    for (int i = 0; i < rows->count; i++) {
        ecs_remove(rows->world, rows->entities[i], tag_to_remove);
        ecs_add(rows->world, rows->entities[i], tag_to_add);
    }
}

void system_test_update(ecs_rows_t *rows) {
    printf("updating\n");
}

int main(int argc, char *argv[]) {
    ecs_world_t *world = ecs_init_w_args(argc, argv);
    ECS_TAG(world, tag_evens);
    ECS_TAG(world, tag_odds);
    ECS_SYSTEM(world, system_test_update, EcsOnUpdate, 0);

    ECS_SYSTEM(world, system_evens, EcsOnUpdate, tag_evens, .tag_odds);

    ECS_SYSTEM(world, system_odds, EcsOnUpdate, tag_odds, .tag_evens);

    int break_condition = 100;

    ECS_TYPE(world, Dummy, tag_evens);
    ecs_new_w_count(world, Dummy, 1);

    while (ecs_progress(world, 0) && break_condition--);

    ecs_fini(world);
}