perf(core): Short-circuit combined scope breadcrumbs

Avoid allocating and sorting a merged breadcrumb queue when only one component scope has breadcrumbs. This keeps the full merge path for multi-scope breadcrumbs and returns the default write scope queue when all scopes are empty.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: adinauer

sentry/src/main/java/io/sentry/CombinedScopeView.java

@@ -171,10 +171,31 @@ public void setFingerprint(@NotNull List<String> fingerprint) {
 
   @Override
   public @NotNull Queue<Breadcrumb> getBreadcrumbs() {
+    final @NotNull Queue<Breadcrumb> globalBreadcrumbs = globalScope.getBreadcrumbs();
+    final @NotNull Queue<Breadcrumb> isolationBreadcrumbs = isolationScope.getBreadcrumbs();
+    final @NotNull Queue<Breadcrumb> currentBreadcrumbs = scope.getBreadcrumbs();
+
+    final boolean hasGlobalBreadcrumbs = !globalBreadcrumbs.isEmpty();
+    final boolean hasIsolationBreadcrumbs = !isolationBreadcrumbs.isEmpty();
+    final boolean hasCurrentBreadcrumbs = !currentBreadcrumbs.isEmpty();
+
+    if (!hasGlobalBreadcrumbs && !hasIsolationBreadcrumbs && !hasCurrentBreadcrumbs) {
+      return getDefaultWriteScope().getBreadcrumbs();
+    }
+    if (!hasIsolationBreadcrumbs && !hasCurrentBreadcrumbs) {
+      return globalBreadcrumbs;
+    }
+    if (!hasGlobalBreadcrumbs && !hasCurrentBreadcrumbs) {
+      return isolationBreadcrumbs;
+    }
+    if (!hasGlobalBreadcrumbs && !hasIsolationBreadcrumbs) {
+      return currentBreadcrumbs;
+    }
+
     final @NotNull List<Breadcrumb> allBreadcrumbs = new ArrayList<>();
-    allBreadcrumbs.addAll(globalScope.getBreadcrumbs());
-    allBreadcrumbs.addAll(isolationScope.getBreadcrumbs());
-    allBreadcrumbs.addAll(scope.getBreadcrumbs());
+    allBreadcrumbs.addAll(globalBreadcrumbs);
+    allBreadcrumbs.addAll(isolationBreadcrumbs);
+    allBreadcrumbs.addAll(currentBreadcrumbs);
     Collections.sort(allBreadcrumbs);
 
     final @NotNull Queue<Breadcrumb> breadcrumbs =

sentry/src/test/java/io/sentry/CombinedScopeViewTest.kt

@@ -11,6 +11,7 @@ import junit.framework.TestCase.assertTrue
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
+import kotlin.test.assertNotSame
 import kotlin.test.assertNull
 import kotlin.test.assertSame
 import org.junit.Assert.assertNotEquals
@@ -72,6 +73,42 @@ class CombinedScopeViewTest {
     assertEquals("current 2", breadcrumbs.poll().message)
   }
 
+  @Test
+  fun `returns single non-empty breadcrumb queue directly`() {
+    var combined = fixture.getSut()
+    fixture.globalScope.addBreadcrumb(Breadcrumb.info("global"))
+    assertSame(fixture.globalScope.breadcrumbs, combined.breadcrumbs)
+
+    combined = fixture.getSut()
+    fixture.isolationScope.addBreadcrumb(Breadcrumb.info("isolation"))
+    assertSame(fixture.isolationScope.breadcrumbs, combined.breadcrumbs)
+
+    combined = fixture.getSut()
+    fixture.scope.addBreadcrumb(Breadcrumb.info("current"))
+    assertSame(fixture.scope.breadcrumbs, combined.breadcrumbs)
+  }
+
+  @Test
+  fun `returns default write scope breadcrumbs when all scopes are empty`() {
+    val combined = fixture.getSut(SentryOptions().also { it.defaultScopeType = ScopeType.CURRENT })
+
+    assertSame(fixture.scope.breadcrumbs, combined.breadcrumbs)
+  }
+
+  @Test
+  fun `returns merged breadcrumb copy when multiple scopes have breadcrumbs`() {
+    val combined = fixture.getSut()
+
+    fixture.globalScope.addBreadcrumb(Breadcrumb.info("global"))
+    fixture.isolationScope.addBreadcrumb(Breadcrumb.info("isolation"))
+
+    val breadcrumbs = combined.breadcrumbs
+
+    assertNotSame(fixture.globalScope.breadcrumbs, breadcrumbs)
+    assertNotSame(fixture.isolationScope.breadcrumbs, breadcrumbs)
+    assertEquals(2, breadcrumbs.size)
+  }
+
   @Test
   fun `oldest breadcrumbs are dropped first`() {
     val options = SentryOptions().also { it.maxBreadcrumbs = 5 }