Properly link flecs library

engine/libs/flecs/examples/c/rules/transitive_queries/include/transitive_queries.h

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+#ifndef TRANSITIVE_QUERIES_H
+#define TRANSITIVE_QUERIES_H
+
+/* This generated file contains includes for project dependencies */
+#include "transitive_queries/bake_config.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+

engine/libs/flecs/examples/c/rules/transitive_queries/include/transitive_queries/bake_config.h

@@ -0,0 +1,24 @@
+/*
+                                   )
+                                  (.)
+                                  .|.
+                                  | |
+                              _.--| |--._
+                           .-';  ;`-'& ; `&.
+                          \   &  ;    &   &_/
+                           |"""---...---"""|
+                           \ | | | | | | | /
+                            `---.|.|.|.---'
+
+ * This file is generated by bake.lang.c for your convenience. Headers of
+ * dependencies will automatically show up in this file. Include bake_config.h
+ * in your main project file. Do not edit! */
+
+#ifndef TRANSITIVE_QUERIES_BAKE_CONFIG_H
+#define TRANSITIVE_QUERIES_BAKE_CONFIG_H
+
+/* Headers of public dependencies */
+#include <flecs.h>
+
+#endif
+

engine/libs/flecs/examples/c/rules/transitive_queries/project.json

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+{
+    "id": "transitive_queries",
+    "type": "application",
+    "value": {
+        "use": [
+            "flecs"
+        ],
+        "public": false
+    }
+}

engine/libs/flecs/examples/c/rules/transitive_queries/src/main.c

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+#include <transitive_queries.h>
+#include <stdio.h>
+
+// Transitive relationships make it possible to tell the ECS that if an entity
+// has a relationship (R, X) and X has relationship (R, Y), the entity should be
+// treated as if it also has (R, Y). In practice this is useful for expressing
+// things like:
+//
+// Bob lives in SanFrancisco
+// San Francisco is located in the United States
+// Therefore Bob also lives in the United States.
+//
+// An example of transitivity can be seen in the component_inheritance example.
+// This example uses the builtin IsA relationship, which is transitive. This
+// example shows how to achieve similar behavior with a user-defined relationship.
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    // LocatedIn relationship
+    ecs_entity_t LocatedIn = ecs_new_id(ecs);
+    ecs_add_id(ecs, LocatedIn, EcsTransitive);
+
+    // Tags
+    ECS_TAG(ecs, Planet);
+    ECS_TAG(ecs, Continent);
+    ECS_TAG(ecs, Country);
+    ECS_TAG(ecs, State);
+    ECS_TAG(ecs, City);
+    ECS_TAG(ecs, Person);
+
+    // Populate the store with locations
+    ecs_entity_t earth = ecs_new_entity(ecs, "Earth");
+    ecs_add(ecs, earth, Planet);
+
+    // Continents
+    ecs_entity_t north_america = ecs_new_entity(ecs, "NorthAmerica");
+    ecs_add(ecs, north_america, Continent);
+    ecs_add_pair(ecs, north_america, LocatedIn, earth);
+
+    ecs_entity_t europe = ecs_new_entity(ecs, "Europe");
+    ecs_add(ecs, europe, Continent);
+    ecs_add_pair(ecs, europe, LocatedIn, earth);
+
+    // Countries
+    ecs_entity_t united_states = ecs_new_entity(ecs, "UnitedStates");
+    ecs_add(ecs, united_states, Country);
+    ecs_add_pair(ecs, united_states, LocatedIn, north_america);
+
+    ecs_entity_t netherlands = ecs_new_entity(ecs, "Netherlands");
+    ecs_add(ecs, netherlands, Country);
+    ecs_add_pair(ecs, netherlands, LocatedIn, europe);
+
+    // States
+    ecs_entity_t california = ecs_new_entity(ecs, "California");
+    ecs_add(ecs, california, State);
+    ecs_add_pair(ecs, california, LocatedIn, united_states);
+
+    ecs_entity_t washington = ecs_new_entity(ecs, "Washington");
+    ecs_add(ecs, washington, State);
+    ecs_add_pair(ecs, washington, LocatedIn, united_states);
+
+    ecs_entity_t noord_holland = ecs_new_entity(ecs, "NoordHolland");
+    ecs_add(ecs, noord_holland, State);
+    ecs_add_pair(ecs, noord_holland, LocatedIn, netherlands);
+
+    // Cities
+    ecs_entity_t san_francisco = ecs_new_entity(ecs, "SanFrancisco");
+    ecs_add(ecs, san_francisco, City);
+    ecs_add_pair(ecs, san_francisco, LocatedIn, california);
+
+    ecs_entity_t seattle = ecs_new_entity(ecs, "Seattle");
+    ecs_add(ecs, seattle, City);
+    ecs_add_pair(ecs, seattle, LocatedIn, washington);
+
+    ecs_entity_t amsterdam = ecs_new_entity(ecs, "Amsterdam");
+    ecs_add(ecs, amsterdam, City);
+    ecs_add_pair(ecs, amsterdam, LocatedIn, noord_holland);
+
+    // Inhabitants
+    ecs_entity_t bob = ecs_new_entity(ecs, "Bob");
+    ecs_add(ecs, bob, Person);
+    ecs_add_pair(ecs, bob, LocatedIn, san_francisco);
+
+    ecs_entity_t alice = ecs_new_entity(ecs, "Alice");
+    ecs_add(ecs, alice, Person);
+    ecs_add_pair(ecs, alice, LocatedIn, seattle);
+
+    ecs_entity_t job = ecs_new_entity(ecs, "Job");
+    ecs_add(ecs, job, Person);
+    ecs_add_pair(ecs, job, LocatedIn, amsterdam);
+
+    // Create a query that finds the countries persons live in. Note that these
+    // have not been explicitly added to the Person entities, but because the
+    // LocatedIn is transitive, the rule engine will traverse the relationship
+    // until it found something that is a country.
+    // 
+    // The equivalent of this query in the DSL is:
+    //   Person, (LocatedIn, $Location), Country($Location)
+    ecs_rule_t *r = ecs_rule(ecs, {
+        .terms = {
+            { .id = Person },
+            { 
+                .first.id = LocatedIn, 
+                .second = { .name = "Location", .flags = EcsIsVariable },
+            },
+            {
+                .first.id = Country, 
+                .src = { .name = "Location", .flags = EcsIsVariable },
+            },
+        }
+    });
+
+    // Lookup the index of the variable. This will let us quickly lookup its
+    // value while we're iterating.
+    int location_var = ecs_rule_find_var(r, "Location");
+
+    // Iterate the rule
+    ecs_iter_t it = ecs_rule_iter(ecs, r);
+    while (ecs_rule_next(&it)) {
+        ecs_entity_t location = ecs_iter_get_var(&it, location_var);
+        for (int i = 0; i < it.count; i ++) {
+            printf("%s lives in %s\n",
+                ecs_get_name(ecs, it.entities[i]),
+                ecs_get_name(ecs, location));
+        }
+    }
+
+    ecs_rule_fini(r);
+
+    // Output:
+    //   Bob lives in UnitedStates
+    //   Alice lives in UnitedStates
+    //   Job lives in Netherlands
+
+    return ecs_fini(ecs);
+}