Properly link flecs library

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

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+/*
+                                   )
+                                  (.)
+                                  .|.
+                                  | |
+                              _.--| |--._
+                           .-';  ;`-'& ; `&.
+                          \   &  ;    &   &_/
+                           |"""---...---"""|
+                           \ | | | | | | | /
+                            `---.|.|.|.---'
+
+ * 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/cpp/rules/transitive_queries/project.json

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

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

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+#include <transitive_queries.h>
+#include <iostream>
+
+// 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.
+
+struct LocatedIn { };
+struct Planet { };
+struct Continent { };
+struct Country { };
+struct State { };
+struct City { };
+struct Person { };
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Register the LocatedIn relationship as transitive
+    ecs.component<LocatedIn>().add(flecs::Transitive);
+
+    // Populate the store with locations
+    flecs::entity earth = ecs.entity("Earth")
+        .add<Planet>();
+
+    // Continents
+    flecs::entity north_america = ecs.entity("NorthAmerica")
+        .add<Continent>()
+        .add<LocatedIn>(earth);
+
+    flecs::entity europe = ecs.entity("Europe")
+        .add<Continent>()
+        .add<LocatedIn>(earth);
+
+    // Countries
+    flecs::entity united_states = ecs.entity("UnitedStates")
+        .add<Country>()
+        .add<LocatedIn>(north_america);
+
+    flecs::entity netherlands = ecs.entity("Netherlands")
+        .add<Country>()
+        .add<LocatedIn>(europe);
+
+    // States
+    flecs::entity california = ecs.entity("California")
+        .add<State>()
+        .add<LocatedIn>(united_states);
+
+    flecs::entity washington = ecs.entity("Washington")
+        .add<State>()
+        .add<LocatedIn>(united_states);
+
+    flecs::entity noord_holland = ecs.entity("NoordHolland")
+        .add<State>()
+        .add<LocatedIn>(netherlands);
+
+    // Cities
+    flecs::entity san_francisco = ecs.entity("SanFrancisco")
+        .add<City>()
+        .add<LocatedIn>(california);
+
+    flecs::entity seattle = ecs.entity("Seattle")
+        .add<City>()
+        .add<LocatedIn>(washington);
+
+    flecs::entity amsterdam = ecs.entity("Amsterdam")
+        .add<City>()
+        .add<LocatedIn>(noord_holland);
+
+    // Inhabitants
+    ecs.entity("Bob")
+        .add<Person>()
+        .add<LocatedIn>(san_francisco);
+
+    ecs.entity("Alice")
+        .add<Person>()
+        .add<LocatedIn>(seattle);
+
+    ecs.entity("Job")
+        .add<Person>()
+        .add<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)
+    flecs::rule<> r = ecs.rule_builder()
+        .with<Person>()
+        .with<LocatedIn>("$Location")
+        .with<Country>().src("$Location")
+        .build();
+    
+    // Lookup the index of the variable. This will let us quickly lookup its
+    // value while we're iterating.
+    int location_var = r.find_var("Location");
+
+    // Iterate the rule
+    r.each([&](flecs::iter& it, size_t index) {
+        std::cout 
+            << it.entity(index).name()
+            << " lives in " << it.get_var(location_var).name()
+            << "\n";
+    });
+
+    // Rules need to be explicitly deleted.
+    r.destruct();
+
+    // Output:
+    //   Bob lives in UnitedStates
+    //   Alice lives in UnitedStates
+    //   Job lives in Netherlands
+}