fix(flags): handle empty evaluation key scopes

.changeset/empty-scopes-stop.md

@@ -0,0 +1,5 @@
+---
+'posthog-php': patch
+---
+
+Return an empty feature flag snapshot without evaluation requests when the requested flag key list is empty.

lib/Client.php

@@ -1044,9 +1044,10 @@ public function getAllFlags(
      * @param bool $disableGeoip Whether to disable GeoIP enrichment during remote evaluation.
      * @param list<string>|null $flagKeys Optional list of flag keys. When provided, only these
      *     flags are evaluated — the underlying /flags request asks the server for just this
-     *     subset, which makes the response smaller and the request cheaper. Use this when you
-     *     only need a handful of flags out of many. Distinct from FeatureFlagEvaluations::only(),
-     *     which scopes which already-evaluated flags get attached to a captured event.
+     *     subset, which makes the response smaller and the request cheaper. An empty list returns
+     *     an empty snapshot without local or remote evaluation. Use this when you only need a
+     *     handful of flags out of many. Distinct from FeatureFlagEvaluations::only(), which scopes
+     *     which already-evaluated flags get attached to a captured event.
      * @return FeatureFlagEvaluations
      */
     public function evaluateFlags(
@@ -1069,6 +1070,15 @@ public function evaluateFlags(
             );
         }
 
+        if ($flagKeys === []) {
+            return new FeatureFlagEvaluations(
+                $distinctId,
+                [],
+                $groups,
+                $this,
+            );
+        }
+
         [$personProperties, $groupProperties] = $this->addLocalPersonAndGroupProperties(
             $groups,
             $personProperties,

test/FeatureFlagEvaluationsTest.php

@@ -289,6 +289,19 @@ public function testCaptureFlagsAttachesFeaturePropertiesWithoutHttpRequest(): v
         }
     }
 
+    public function testEmptyFlagKeysReturnsEmptySnapshotWithoutEvaluationRequests(): void
+    {
+        $this->makeClient();
+        $callsBefore = count($this->http_client->calls ?? []);
+
+        $snapshot = PostHog::evaluateFlags('user-1', flagKeys: []);
+
+        $this->assertInstanceOf(FeatureFlagEvaluations::class, $snapshot);
+        $this->assertSame([], $snapshot->getKeys());
+        $this->assertCount($callsBefore, $this->http_client->calls ?? []);
+        $this->assertSame(0, $this->flagsRequestCount());
+    }
+
     public function testFlagKeysIsForwardedInRequestBody(): void
     {
         $this->makeClient();