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fix(flags): fix failed flag overwrite on individual evaluation error #104

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Merged
matheus-vb merged 1 commit into from
Feb 6, 2026
+173 −1
Merged

fix(flags): fix failed flag overwrite on individual evaluation error #104

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9 changes: 8 additions & 1 deletion lib/Client.php
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Original file line number Diff line number Diff line change
Expand Up @@ -339,7 +339,10 @@ public function getFeatureFlagResult(

$requestId = isset($response['requestId']) ? $response['requestId'] : null;
$evaluatedAt = isset($response['evaluatedAt']) ? $response['evaluatedAt'] : null;
$flagDetail = isset($response['flags'][$key]) ? $response['flags'][$key] : null;
$rawFlag = $response['flags'][$key] ?? null;
$flagDetail = ($rawFlag !== null && !($rawFlag['failed'] ?? false))
? $rawFlag
: null;
$featureFlags = $response['featureFlags'] ?? [];
if (array_key_exists($key, $featureFlags)) {
$result = $featureFlags[$key];
Expand Down Expand Up @@ -720,6 +723,10 @@ private function normalizeFeatureFlags(string $response): array
$transformedFlags = [];
$transformedPayloads = [];
foreach ($decoded['flags'] as $key => $flag) {
// Skip flags that failed evaluation to avoid overwriting cached values
if (isset($flag['failed']) && $flag['failed']) {
continue;
}
if ($flag['variant'] !== null) {
$transformedFlags[$key] = $flag['variant'];
} else {
Expand Down
165 changes: 165 additions & 0 deletions test/FeatureFlagErrorTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -427,4 +427,169 @@ public function testQuotaLimitedError()
$this->assertEquals(FeatureFlagError::QUOTA_LIMITED, $event['properties']['$feature_flag_error']);
});
}

public function testFailedFlagIsFilteredOutByFailedField()
{
$this->executeAtFrozenDateTime(new \DateTime('2022-05-01'), function () {
// V4 response with three flags:
// - 'failed-flag': failed=true (transient error), should be filtered out
// - 'disabled-flag': enabled=false, failed=false (legitimately disabled), should NOT be filtered
// - 'good-flag': enabled=true, failed=false (successful), should NOT be filtered
$responseWithFailedFlag = [
'flags' => [
'failed-flag' => [
'key' => 'failed-flag',
'enabled' => false,
'variant' => null,
'reason' => [
'code' => 'database_error',
'description' => 'Database connection error during evaluation',
'condition_index' => null,
],
'metadata' => ['id' => 1, 'version' => 1, 'payload' => null],
'failed' => true,
],
'disabled-flag' => [
'key' => 'disabled-flag',
'enabled' => false,
'variant' => null,
'reason' => [
'code' => 'condition_match',
'description' => 'No conditions matched',
'condition_index' => null,
],
'metadata' => ['id' => 2, 'version' => 1, 'payload' => null],
'failed' => false,
],
'good-flag' => [
'key' => 'good-flag',
'enabled' => true,
'variant' => null,
'reason' => [
'code' => 'condition_match',
'description' => 'Matched condition set 1',
'condition_index' => 0,
],
'metadata' => ['id' => 3, 'version' => 1, 'payload' => null],
'failed' => false,
],
],
'errorsWhileComputingFlags' => true,
'requestId' => 'test-request-id',
];

$this->setUp($responseWithFailedFlag, personalApiKey: null);

// The failed flag should be filtered out entirely (null, not false)
$failedResult = PostHog::getFeatureFlag('failed-flag', 'user-id');
$this->assertNull($failedResult);

// A legitimately disabled flag (failed=false) should still return false
$disabledResult = PostHog::getFeatureFlag('disabled-flag', 'user-id');
$this->assertFalse($disabledResult);

// A successfully enabled flag should return its value
$goodResult = PostHog::getFeatureFlag('good-flag', 'user-id');
$this->assertTrue($goodResult);
});
}

public function testGetAllFlagsDoesNotOverwriteLocalResultWithFailedServerFlag()
{
$this->executeAtFrozenDateTime(new \DateTime('2022-05-01'), function () {
// Local flags: simple-flag evaluates locally; ec-flag requires server
// due to experience continuity.
$localFlags = [
'flags' => [
[
"id" => 1,
"name" => "",
"key" => "simple-flag",
"filters" => [
"groups" => [
["properties" => [], "rollout_percentage" => 100]
]
],
"deleted" => false,
"active" => true,
"is_simple_flag" => true,
],
[
"id" => 2,
"name" => "EC Feature",
"key" => "ec-flag",
"filters" => [
"groups" => [
["properties" => [], "rollout_percentage" => 100]
]
],
"ensure_experience_continuity" => true,
"deleted" => false,
"active" => true,
"is_simple_flag" => true,
],
],
];

// Server response (v4): simple-flag failed due to transient error,
// ec-flag evaluated successfully.
$serverResponse = [
'flags' => [
'simple-flag' => [
'key' => 'simple-flag',
'enabled' => false,
'variant' => null,
'reason' => [
'code' => 'database_error',
'description' => 'Database connection error',
'condition_index' => null,
],
'metadata' => ['id' => 1, 'version' => 1, 'payload' => null],
'failed' => true,
],
'ec-flag' => [
'key' => 'ec-flag',
'enabled' => true,
'variant' => null,
'reason' => [
'code' => 'condition_match',
'description' => 'Matched condition set 1',
'condition_index' => 0,
],
'metadata' => ['id' => 2, 'version' => 1, 'payload' => null],
'failed' => false,
],
],
'errorsWhileComputingFlags' => true,
'requestId' => 'test-request-id',
];

$this->http_client = new MockedHttpClient(
host: "app.posthog.com",
flagEndpointResponse: $localFlags,
flagsEndpointResponse: $serverResponse
);
$this->client = new Client(
self::FAKE_API_KEY,
["debug" => true],
$this->http_client,
"test" // personal API key enables local evaluation
);
PostHog::init(null, null, $this->client);

global $errorMessages;
$errorMessages = [];

$flags = PostHog::getAllFlags('distinct-id');

// simple-flag was locally evaluated as true. The server returned it
// as failed (enabled=false, failed=true). The failed server result
// must NOT overwrite the local value via array_merge.
$this->assertTrue($flags['simple-flag']);

// ec-flag could not be evaluated locally (experience continuity),
// so the successful server result should be used.
$this->assertTrue($flags['ec-flag']);
});
}
}