Add a method to the Baggage interface to return the current baggage in the context (#1913)

* Add a method to the Baggage interface to return the current baggage in the context.

* formatting

* Fix tests broken by not clearing state

* don't try to code while overly tired. the result is scopes that aren't closed.

* remove the scope to make sure the root scope has no baggage

api/src/main/java/io/opentelemetry/api/baggage/Baggage.java

@@ -31,6 +31,14 @@ public interface Baggage extends ImplicitContextKeyed {
     return ImmutableBaggage.builder();
   }
 
+  /**
+   * Returns Baggage from the current {@link Context}, falling back to empty Baggage if none is in
+   * the current Context.
+   */
+  static Baggage current() {
+    return BaggageUtils.getCurrentBaggage();
+  }
+
   @Override
   default Context storeInContext(Context context) {
     return BaggageUtils.withBaggage(this, context);

api/src/test/java/io/opentelemetry/api/baggage/BaggageTest.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.api.baggage;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.context.Scope;
+import org.junit.jupiter.api.Test;
+
+class BaggageTest {
+  @Test
+  void current_empty() {
+    try (Scope scope = Context.root().makeCurrent()) {
+      assertThat(Baggage.current()).isEqualTo(Baggage.empty());
+    }
+  }
+
+  @Test
+  void current() {
+    try (Scope scope =
+        Context.root()
+            .with(Baggage.builder().put("foo", "bar").setNoParent().build())
+            .makeCurrent()) {
+      Baggage result = Baggage.current();
+      assertThat(result.getEntryValue("foo")).isEqualTo("bar");
+      assertThat(result).isEqualTo(Baggage.builder().setNoParent().put("foo", "bar").build());
+    }
+  }
+}

api/src/test/java/io/opentelemetry/api/baggage/BaggageUtilsTest.java

@@ -15,41 +15,43 @@ class BaggageUtilsTest {
 
   @Test
   void testGetCurrentBaggage_Default() {
-    Baggage baggage = BaggageUtils.getCurrentBaggage();
-    assertThat(baggage).isSameAs(Baggage.empty());
+    try (Scope s = Context.root().makeCurrent()) {
+      Baggage baggage = BaggageUtils.getCurrentBaggage();
+      assertThat(baggage).isSameAs(Baggage.empty());
+    }
   }
 
   @Test
   void testGetCurrentBaggage_SetCorrContext() {
     Baggage baggage = Baggage.empty();
-    try (Scope ignored = BaggageUtils.withBaggage(baggage, Context.current()).makeCurrent()) {
+    try (Scope ignored = BaggageUtils.withBaggage(baggage, Context.root()).makeCurrent()) {
       assertThat(BaggageUtils.getCurrentBaggage()).isSameAs(baggage);
     }
   }
 
   @Test
   void testGetBaggage_DefaultContext() {
-    Baggage baggage = BaggageUtils.getBaggage(Context.current());
+    Baggage baggage = BaggageUtils.getBaggage(Context.root());
     assertThat(baggage).isSameAs(Baggage.empty());
   }
 
   @Test
   void testGetBaggage_ExplicitContext() {
     Baggage baggage = Baggage.empty();
-    Context context = BaggageUtils.withBaggage(baggage, Context.current());
+    Context context = BaggageUtils.withBaggage(baggage, Context.root());
     assertThat(BaggageUtils.getBaggage(context)).isSameAs(baggage);
   }
 
   @Test
   void testGetBaggageWithoutDefault_DefaultContext() {
-    Baggage baggage = BaggageUtils.getBaggageWithoutDefault(Context.current());
+    Baggage baggage = BaggageUtils.getBaggageWithoutDefault(Context.root());
     assertThat(baggage).isNull();
   }
 
   @Test
   void testGetBaggageWithoutDefault_ExplicitContext() {
     Baggage baggage = Baggage.empty();
-    Context context = BaggageUtils.withBaggage(baggage, Context.current());
+    Context context = BaggageUtils.withBaggage(baggage, Context.root());
     assertThat(BaggageUtils.getBaggage(context)).isSameAs(baggage);
   }
 }

api/src/test/java/io/opentelemetry/api/baggage/ImmutableBaggageTest.java

@@ -96,14 +96,14 @@ class ImmutableBaggageTest {
 
   @Test
   void setParent_fromContext() {
-    Context context = Context.current().with(listToBaggage(T2));
+    Context context = Context.root().with(listToBaggage(T2));
     Baggage baggage = Baggage.builder().setParent(context).build();
     assertThat(baggage.getEntries()).containsExactly(T2);
   }
 
   @Test
   void setParent_fromEmptyContext() {
-    Context emptyContext = Context.current();
+    Context emptyContext = Context.root();
     Baggage parent = listToBaggage(T1);
     try (Scope scope = BaggageUtils.currentContextWith(parent)) {
       Baggage baggage = Baggage.builder().setParent(emptyContext).build();