feat: Setting personalApiKey turns local eval on by default

Author: dustinbyrne

posthog-server/src/main/java/com/posthog/server/PostHogConfig.kt

@@ -227,7 +227,7 @@ public open class PostHogConfig constructor(
         private var featureFlagCacheSize: Int = DEFAULT_FEATURE_FLAG_CACHE_SIZE
         private var featureFlagCacheMaxAgeMs: Int = DEFAULT_FEATURE_FLAG_CACHE_MAX_AGE_MS
         private var featureFlagCalledCacheSize: Int = DEFAULT_FEATURE_FLAG_CALLED_CACHE_SIZE
-        private var localEvaluation: Boolean = false
+        private var localEvaluation: Boolean? = null
         private var personalApiKey: String? = null
         private var pollIntervalSeconds: Int = DEFAULT_POLL_INTERVAL_SECONDS
 
@@ -265,7 +265,13 @@ public open class PostHogConfig constructor(
 
         public fun localEvaluation(localEvaluation: Boolean): Builder = apply { this.localEvaluation = localEvaluation }
 
-        public fun personalApiKey(personalApiKey: String?): Builder = apply { this.personalApiKey = personalApiKey }
+        public fun personalApiKey(personalApiKey: String?): Builder =
+            apply {
+                this.personalApiKey = personalApiKey
+                if (localEvaluation == null) {
+                    this.localEvaluation = personalApiKey != null
+                }
+            }
 
         public fun pollIntervalSeconds(pollIntervalSeconds: Int): Builder = apply { this.pollIntervalSeconds = pollIntervalSeconds }
 
@@ -287,7 +293,7 @@ public open class PostHogConfig constructor(
                 featureFlagCacheSize = featureFlagCacheSize,
                 featureFlagCacheMaxAgeMs = featureFlagCacheMaxAgeMs,
                 featureFlagCalledCacheSize = featureFlagCalledCacheSize,
-                localEvaluation = localEvaluation,
+                localEvaluation = localEvaluation ?: false,
                 personalApiKey = personalApiKey,
                 pollIntervalSeconds = pollIntervalSeconds,
             )

posthog-server/src/test/java/com/posthog/server/PostHogConfigTest.kt

@@ -476,4 +476,38 @@ internal class PostHogConfigTest {
         assertEquals(coreConfig1.apiKey, coreConfig2.apiKey)
         assertEquals(coreConfig1.host, coreConfig2.host)
     }
+
+    @Test
+    fun `builder personalApiKey enables localEvaluation when not explicitly set`() {
+        val config =
+            PostHogConfig.builder(TEST_API_KEY)
+                .personalApiKey("test-personal-api-key")
+                .build()
+
+        assertEquals("test-personal-api-key", config.personalApiKey)
+        assertEquals(true, config.localEvaluation)
+    }
+
+    @Test
+    fun `builder personalApiKey with null does not enable localEvaluation when not explicitly set`() {
+        val config =
+            PostHogConfig.builder(TEST_API_KEY)
+                .personalApiKey(null)
+                .build()
+
+        assertNull(config.personalApiKey)
+        assertEquals(false, config.localEvaluation)
+    }
+
+    @Test
+    fun `builder personalApiKey does not override explicit localEvaluation false`() {
+        val config =
+            PostHogConfig.builder(TEST_API_KEY)
+                .localEvaluation(false)
+                .personalApiKey("test-personal-api-key")
+                .build()
+
+        assertEquals("test-personal-api-key", config.personalApiKey)
+        assertEquals(false, config.localEvaluation)
+    }
 }