Fix invalid shaded helper package names

dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/AdviceShader.java

@@ -1,5 +1,6 @@
 package datadog.trace.agent.tooling;
 
+import static java.lang.Integer.toHexString;
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
 
@@ -84,9 +85,10 @@ public byte[] shadeClass(byte[] bytecode) {
   public String uniqueHelper(String dottedName) {
     int packageEnd = dottedName.lastIndexOf('.');
     if (packageEnd > 0) {
+      // Hex encoding keeps negative hashes valid in Java package names.
       return dottedName.substring(0, packageEnd + 1)
           + "shaded"
-          + relocations.hashCode()
+          + toHexString(relocations.hashCode())
           + dottedName.substring(packageEnd);
     }
     return dottedName;

dd-java-agent/agent-tooling/src/test/java/datadog/trace/agent/tooling/AdviceShaderTest.java

@@ -0,0 +1,62 @@
+package datadog.trace.agent.tooling;
+
+import static java.util.Collections.singletonMap;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+import org.tabletest.junit.TableTest;
+
+class AdviceShaderTest {
+  private static final String HELPER = "datadog.trace.instrumentation.jms.DatadogMessageListener";
+
+  @TableTest({
+    "scenario         | relocation         ",
+    "zero hash        | ''                 ",
+    "positive hash    | a                  ",
+    "minimum int hash | min-hash-7052265601"
+  })
+  void helperPackageIsAJavaIdentifierForEveryHashSign(String relocation) {
+    AdviceShader shader = AdviceShader.with(singletonMap("", relocation));
+
+    assertValidClassName(shader.uniqueHelper(HELPER));
+  }
+
+  @Test
+  void jakartaJmsHelperNamesAndReferencesMatch() {
+    InstrumenterModule module =
+        new InstrumenterModule("test-jakarta-jms") {
+          @Override
+          public Map<String, String> adviceShading() {
+            return singletonMap("javax", "jakarta");
+          }
+
+          @Override
+          public String[] helperClassNames() {
+            return new String[] {HELPER};
+          }
+        };
+    AdviceShader shader = AdviceShader.with(module);
+    String shadedHelper = shader.uniqueHelper(HELPER);
+
+    assertTrue(module.adviceShading().hashCode() < 0);
+    assertValidClassName(shadedHelper);
+    assertNotEquals(HELPER, shadedHelper);
+    assertEquals(shadedHelper, shader.shadeClassName(HELPER));
+    assertEquals(
+        "L" + shadedHelper.replace('.', '/') + ";",
+        shader.shadeTypeDescriptor("L" + HELPER.replace('.', '/') + ";"));
+    assertEquals("jakarta.jms.MessageListener", shader.shadeClassName("javax.jms.MessageListener"));
+  }
+
+  private static void assertValidClassName(String className) {
+    for (String segment : className.split("\\.")) {
+      assertTrue(Character.isJavaIdentifierStart(segment.charAt(0)), className);
+      for (int i = 1; i < segment.length(); i++) {
+        assertTrue(Character.isJavaIdentifierPart(segment.charAt(i)), className);
+      }
+    }
+  }
+}