make sure resource is set when getting it (to help troubleshoot)

Author: zeitlinger

sdk-extensions/incubator/src/main/java/io/opentelemetry/sdk/extension/incubator/fileconfig/DeclarativeConfigContext.java

@@ -26,7 +26,7 @@ class DeclarativeConfigContext {
   private final SpiHelper spiHelper;
   private final List<Closeable> closeables = new ArrayList<>();
   @Nullable private volatile MeterProvider meterProvider;
-  private Resource resource = Resource.empty();
+  @Nullable private Resource resource = null;
 
   // Visible for testing
   DeclarativeConfigContext(SpiHelper spiHelper) {
@@ -61,6 +61,9 @@ public void setMeterProvider(MeterProvider meterProvider) {
 
   Resource getResource() {
     // called via reflection from io.opentelemetry.sdk.autoconfigure.IncubatingUtil
+    if (resource == null) {
+      throw new DeclarativeConfigException("Resource has not been configured yet.");
+    }
     return resource;
   }
 

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/fileconfig/DeclarativeConfigContextTest.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.extension.incubator.fileconfig;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+
+import io.opentelemetry.api.incubator.config.DeclarativeConfigException;
+import io.opentelemetry.common.ComponentLoader;
+import io.opentelemetry.sdk.resources.Resource;
+import org.junit.jupiter.api.Test;
+
+class DeclarativeConfigContextTest {
+
+  private final DeclarativeConfigContext context =
+      DeclarativeConfigContext.create(
+          ComponentLoader.forClassLoader(DeclarativeConfigContextTest.class.getClassLoader()));
+
+  @Test
+  void resourceMustBeSetBeforeUse() {
+    assertThatCode(context::getResource).isInstanceOf(DeclarativeConfigException.class);
+    Resource resource = Resource.empty();
+    context.setResource(resource);
+    assertThat(context.getResource()).isSameAs(resource);
+  }
+}