add isDeclarative

Author: zeitlinger

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/config/internal/InstrumentationConfig.java

@@ -110,9 +110,14 @@ default List<String> getList(String name) {
    */
   Map<String, String> getMap(String name, Map<String, String> defaultValue);
 
+  /** Returns {@code true} if declarative configuration is used in this configuration. */
+  boolean isDeclarative();
+
   /**
-   * Returns a {@link DeclarativeConfigProperties} for the given instrumentation name, or {@code
-   * null} if declarative configuration is <b>not used at all</b>.
+   * Returns a {@link DeclarativeConfigProperties} for the given node name, which is usually an
+   * instrumentation name
+   *
+   * <p>Call {@link #isDeclarative()} first to check if declarative configuration is used.
    *
    * <p>Declarative configuration is used to configure instrumentation properties in a declarative
    * way, such as through YAML or JSON files.
@@ -121,8 +126,8 @@ default List<String> getList(String name) {
    *     "common" for common Java settings that don't apply to other languages.
    * @return the declarative configuration properties for the given node name, or {@code null} if
    *     declarative configuration is <b>not used at all</b>.
+   * @throws IllegalStateException if {@link #isDeclarative()} returns {@code false}
    */
-  @Nullable
   DeclarativeConfigProperties getDeclarativeConfig(String node);
 
   /**

instrumentation/methods/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/methods/MethodInstrumentationModule.java

@@ -10,8 +10,8 @@
 import static java.util.Collections.singletonMap;
 
 import com.google.auto.service.AutoService;
-import io.opentelemetry.api.incubator.config.DeclarativeConfigProperties;
 import io.opentelemetry.api.trace.SpanKind;
+import io.opentelemetry.instrumentation.api.incubator.config.internal.InstrumentationConfig;
 import io.opentelemetry.javaagent.bootstrap.internal.AgentInstrumentationConfig;
 import io.opentelemetry.javaagent.extension.instrumentation.InstrumentationModule;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
@@ -34,10 +34,11 @@ public MethodInstrumentationModule() {
   }
 
   private static List<TypeInstrumentation> createInstrumentations() {
-    DeclarativeConfigProperties methods =
-        AgentInstrumentationConfig.get().getDeclarativeConfig("methods");
+    InstrumentationConfig config = AgentInstrumentationConfig.get();
     List<TypeInstrumentation> list =
-        methods != null ? MethodsConfig.parseDeclarativeConfig(methods) : parseConfigProperties();
+        config.isDeclarative()
+            ? MethodsConfig.parseDeclarativeConfig(config.getDeclarativeConfig("methods"))
+            : parseConfigProperties();
     // ensure that there is at least one instrumentation so that muzzle reference collection could
     // work
     if (list.isEmpty()) {

instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/ConfigPropertiesBridge.java

@@ -111,17 +111,21 @@ public Map<String, String> getMap(String name, Map<String, String> defaultValue)
     }
   }
 
-  @Nullable
+  @Override
+  public boolean isDeclarative() {
+    return false;
+  }
+
   @Override
   public DeclarativeConfigProperties getDeclarativeConfig(String node) {
-    // create a spring boot bridge for DeclarativeConfigProperties
-    return null;
+    throw new IllegalStateException(
+        "Declarative configuration is not supported in spring boot autoconfigure yet");
   }
 
   @Nullable
   @Override
   public ConfigProvider getConfigProvider() {
-    // create a spring boot bridge for ConfigProvider
+    // declarative config support will be added in the future
     return null;
   }
 }

javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/bootstrap/internal/EmptyInstrumentationConfig.java

@@ -61,10 +61,15 @@ public Map<String, String> getMap(String name, Map<String, String> defaultValue)
     return defaultValue;
   }
 
-  @Nullable
+  @Override
+  public boolean isDeclarative() {
+    return false;
+  }
+
   @Override
   public DeclarativeConfigProperties getDeclarativeConfig(String node) {
-    return null;
+    throw new IllegalStateException(
+        "Declarative configuration is not supported in the empty instrumentation config");
   }
 
   @Nullable

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/config/ConfigPropertiesBridge.java

@@ -111,12 +111,15 @@ public Map<String, String> getMap(String name, Map<String, String> defaultValue)
     }
   }
 
-  @Nullable
+  @Override
+  public boolean isDeclarative() {
+    return configProvider != null;
+  }
+
   @Override
   public DeclarativeConfigProperties getDeclarativeConfig(String node) {
-    if (configProvider == null) {
-      // declarative config is not used
-      return null;
+    if (!isDeclarative()) {
+      throw new IllegalStateException("Declarative configuration is not supported");
     }
 
     DeclarativeConfigProperties config =