fix(flipt): Fix FliptProvider to honor server default variant when match is false (#1776)

Signed-off-by: Dariusz Szyszlak <dariusz.szyszlak@gmail.com>

Author: Openroads

providers/flipt/src/main/java/dev/openfeature/contrib/providers/flipt/FliptProvider.java

@@ -178,8 +178,9 @@ private <T> ProviderEvaluation<Value> evaluateVariant(
             log.error("Error evaluating variant", e);
             throw new GeneralError(e.getMessage());
         }
-
-        if (!response.isMatch()) {
+        boolean hasVariantKey =
+                response.getVariantKey() != null && !response.getVariantKey().isEmpty();
+        if (!response.isMatch() && !hasVariantKey) {
             log.debug("non matching variant for {} : {}", key, response.getReason());
             return ProviderEvaluation.<Value>builder()
                     .value(defaultValue)
@@ -201,7 +202,10 @@ private <T> ProviderEvaluation<Value> evaluateVariant(
         return ProviderEvaluation.<Value>builder()
                 .value(value)
                 .variant(response.getVariantKey())
-                .reason(TARGETING_MATCH.name())
+                .reason(
+                        response.isMatch()
+                                ? TARGETING_MATCH.name()
+                                : response.getReason().toString())
                 .flagMetadata(flagMetadataBuilder.build())
                 .build();
     }

providers/flipt/src/test/java/dev/openfeature/contrib/providers/flipt/FliptProviderTest.java

@@ -110,6 +110,25 @@ void getStringVariantEvaluation() {
         assertEquals("fallback_str", client.getStringValue("non-existing", "fallback_str", evaluationContext));
     }
 
+    @Test
+    void getStringVariantEvaluation_usesServerDefaultVariantWhenNoMatch() {
+        // Flipt returns match=false but still returns a variantKey (server default variant).
+        mockFliptAPI("/evaluate/v1/variant", "variant-default-nomatch.json", VARIANT_FLAG_NAME);
+
+        MutableContext evaluationContext = new MutableContext();
+        evaluationContext.setTargetingKey(TARGETING_KEY);
+
+        // SDK defaultValue should NOT be used in this case; server default variant should win.
+        ProviderEvaluation<String> evaluation =
+                fliptProvider.getStringEvaluation(VARIANT_FLAG_NAME, "sdk-fallback", evaluationContext);
+
+        assertEquals("server-default", evaluation.getValue());
+        assertEquals("server-default", evaluation.getVariant());
+
+        // Also verify the OpenFeature client path.
+        assertEquals("server-default", client.getStringValue(VARIANT_FLAG_NAME, "sdk-fallback", evaluationContext));
+    }
+
     @Test
     void getIntegerEvaluation() {
         mockFliptAPI("/evaluate/v1/variant", "variant-int.json", INT_FLAG_NAME);

providers/flipt/src/test/resources/variant-default-nomatch.json

@@ -0,0 +1,10 @@
+{
+  "match": false,
+  "reason": "DEFAULT_EVALUATION_REASON",
+  "requestDurationMillis": 1,
+  "requestId": "string",
+  "segmentKeys": [],
+  "timestamp": "2022-12-03T10:15:30+01:00",
+  "variantAttachment": "",
+  "variantKey": "server-default"
+}