RecipeMarketplace.Category.merge: copy unmatched source children

rewrite-core/src/main/java/org/openrewrite/marketplace/RecipeMarketplace.java

@@ -84,11 +84,11 @@ public void merge(Category category) {
                         break;
                     }
                 }
-                if (existingSubCategory != null) {
-                    existingSubCategory.merge(subCategory);
-                } else {
-                    categories.add(subCategory);
+                if (existingSubCategory == null) {
+                    existingSubCategory = new Category(subCategory.getDisplayName(), subCategory.getDescription());
+                    categories.add(existingSubCategory);
                 }
+                existingSubCategory.merge(subCategory);
             }
         }
 

rewrite-core/src/test/java/org/openrewrite/marketplace/RecipeMarketplaceMergeTest.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2026 the original author or authors.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.marketplace;
+
+import org.intellij.lang.annotations.Language;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RecipeMarketplaceMergeTest {
+
+    @Test
+    void mergeAllocatesFreshCategoriesOnTarget() {
+        // The receiver must own every Category instance it holds. If `merge` adopts
+        // the source's child by reference, a subsequent merge that name-matches
+        // into the receiver recurses into and mutates the original source.
+        @Language("csv") String csv = """
+          name,category1,ecosystem,packageName
+          org.example.A,Testing,maven,org.example:test
+          """;
+        RecipeMarketplace source = new RecipeMarketplaceReader().fromCsv(csv);
+        RecipeMarketplace target = new RecipeMarketplace();
+
+        target.getRoot().merge(source.getRoot());
+
+        RecipeMarketplace.Category sourceTesting = findCategory(source.getRoot(), "Testing");
+        RecipeMarketplace.Category targetTesting = findCategory(target.getRoot(), "Testing");
+        assertThat(targetTesting).isNotSameAs(sourceTesting);
+    }
+
+    @Test
+    void mergeIntoFreshTargetDoesNotMutateSource() {
+        // Layering universal + org into a fresh result must leave both inputs
+        // untouched — otherwise long-lived (cached) sources accumulate recipes
+        // from every previous merge they were a layer of.
+        @Language("csv") String universalCsv = """
+          name,category1,ecosystem,packageName
+          org.example.universalA,Testing,maven,org.example:test
+          org.example.universalB,Testing,maven,org.example:test
+          """;
+        @Language("csv") String orgCsv = """
+          name,category1,ecosystem,packageName
+          org.example.orgC,Testing,maven,org.example:test
+          """;
+        RecipeMarketplace universal = new RecipeMarketplaceReader().fromCsv(universalCsv);
+        RecipeMarketplace org = new RecipeMarketplaceReader().fromCsv(orgCsv);
+
+        var universalNamesBefore = universal.getAllRecipes().stream()
+                .map(RecipeListing::getName).sorted().toList();
+        var orgNamesBefore = org.getAllRecipes().stream()
+                .map(RecipeListing::getName).sorted().toList();
+
+        RecipeMarketplace result = new RecipeMarketplace();
+        result.getRoot().merge(universal.getRoot());
+        result.getRoot().merge(org.getRoot());
+
+        assertThat(universal.getAllRecipes().stream().map(RecipeListing::getName).sorted().toList())
+                .as("universal must not gain recipes from later merges")
+                .isEqualTo(universalNamesBefore);
+        assertThat(org.getAllRecipes().stream().map(RecipeListing::getName).sorted().toList())
+                .as("org must not gain recipes from earlier merges")
+                .isEqualTo(orgNamesBefore);
+        assertThat(result.getAllRecipes()).extracting(RecipeListing::getName)
+                .containsExactlyInAnyOrder(
+                        "org.example.universalA",
+                        "org.example.universalB",
+                        "org.example.orgC");
+    }
+
+    private static RecipeMarketplace.Category findCategory(
+            RecipeMarketplace.Category parent, String displayName) {
+        for (RecipeMarketplace.Category c : parent.getCategories()) {
+            if (c.getDisplayName().equalsIgnoreCase(displayName)) {
+                return c;
+            }
+        }
+        throw new AssertionError("Category not found: " + displayName);
+    }
+}