AddToTagVisitor: skip insert when a semantically-equal child exists

Make `AddToTagVisitor` idempotent: if `scope` already contains a
`SemanticallyEqual` child, return without mutating the tree. This
preserves reference identity on no-op runs so that "did this recipe
change anything" checks (and dependent dirty-tracking) stay accurate.

Comments and attribute order are ignored by the equality check, so
re-running a recipe over input it has already processed no longer
produces a duplicate child.

Author: steve-aom-elliott

rewrite-xml/src/main/java/org/openrewrite/xml/AddToTagVisitor.java

@@ -46,6 +46,13 @@ public AddToTagVisitor(Xml.Tag scope, Xml.Tag tagToAdd, @Nullable Comparator<Con
     @Override
     public Xml visitTag(Xml.Tag t, P p) {
         if (scope.isScope(t)) {
+            if (t.getContent() != null) {
+                for (Content existing : t.getContent()) {
+                    if (existing instanceof Xml.Tag && SemanticallyEqual.areEqual(existing, tagToAdd)) {
+                        return super.visitTag(t, p);
+                    }
+                }
+            }
             assert getCursor().getParent() != null;
             if (t.getClosing() == null) {
                 t = t.withClosing(autoFormat(new Xml.Tag.Closing(Tree.randomId(), "\n",

rewrite-xml/src/test/java/org/openrewrite/xml/AddToTagTest.java

@@ -143,6 +143,73 @@ public Xml visitDocument(Xml.Document x, ExecutionContext ctx) {
         );
     }
 
+    @Test
+    void doesNotAddSemanticallyEqualDuplicate() {
+        rewriteRun(
+          spec -> spec.recipe(toRecipe(() -> new XmlVisitor<>() {
+              @Override
+              public Xml visitDocument(Xml.Document x, ExecutionContext ctx) {
+                  doAfterVisit(new AddToTagVisitor<>(x.getRoot(), Xml.Tag.build("<bean id=\"myBean\"/>")));
+                  return super.visitDocument(x, ctx);
+              }
+          })),
+          xml(
+            """
+              <beans>
+                <bean id="myBean"/>
+              </beans>
+              """
+          )
+        );
+    }
+
+    @Test
+    void doesNotAddDuplicateIgnoringAttributeOrder() {
+        rewriteRun(
+          spec -> spec.recipe(toRecipe(() -> new XmlVisitor<>() {
+              @Override
+              public Xml visitDocument(Xml.Document x, ExecutionContext ctx) {
+                  doAfterVisit(new AddToTagVisitor<>(x.getRoot(),
+                          Xml.Tag.build("<bean class=\"C\" id=\"myBean\"/>")));
+                  return super.visitDocument(x, ctx);
+              }
+          })),
+          xml(
+            """
+              <beans>
+                <bean id="myBean" class="C"/>
+              </beans>
+              """
+          )
+        );
+    }
+
+    @Test
+    void addsWhenChildrenShareNameButDifferentAttributes() {
+        rewriteRun(
+          spec -> spec.recipe(toRecipe(() -> new XmlVisitor<>() {
+              @Override
+              public Xml visitDocument(Xml.Document x, ExecutionContext ctx) {
+                  doAfterVisit(new AddToTagVisitor<>(x.getRoot(), Xml.Tag.build("<bean id=\"myBean2\"/>")));
+                  return super.visitDocument(x, ctx);
+              }
+          })),
+          xml(
+            """
+              <beans>
+                <bean id="myBean"/>
+              </beans>
+              """,
+            """
+              <beans>
+                <bean id="myBean"/>
+                <bean id="myBean2"/>
+              </beans>
+              """
+          )
+        );
+    }
+
     @Issue("https://github.com/openrewrite/rewrite/issues/1392")
     @Test
     void preserveNonTagContent() {