[JENKINS-74933] Allow ConfigurationContext to use a specific mergeStr…

…ategy (#2602)

Co-authored-by: Tim Jacomb <[email protected]>

plugin/src/main/java/io/jenkins/plugins/casc/ConfigurationContext.java

@@ -45,13 +45,19 @@ public class ConfigurationContext implements ConfiguratorRegistry {
     private transient SecretSourceResolver secretSourceResolver;
 
     public ConfigurationContext(ConfiguratorRegistry registry) {
+        this(registry, null);
+    }
+
+    public ConfigurationContext(ConfiguratorRegistry registry, String mergeStrategy) {
         this.registry = registry;
         String prop = getPropertyOrEnv(CASC_YAML_MAX_ALIASES_ENV, CASC_YAML_MAX_ALIASES_PROPERTY);
         yamlMaxAliasesForCollections = NumberUtils.toInt(prop, 50);
         prop = getPropertyOrEnv(CASC_YAML_CODE_POINT_LIMIT_ENV, CASC_YAML_CODE_POINT_LIMIT_PROPERTY);
         yamlCodePointLimit = NumberUtils.toInt(prop, 3) * 1024 * 1024;
         secretSourceResolver = new SecretSourceResolver(this);
-        mergeStrategy = getPropertyOrEnv(CASC_MERGE_STRATEGY_ENV, CASC_MERGE_STRATEGY_PROPERTY);
+        this.mergeStrategy = mergeStrategy != null
+                ? mergeStrategy
+                : getPropertyOrEnv(CASC_MERGE_STRATEGY_ENV, CASC_MERGE_STRATEGY_PROPERTY);
     }
 
     private String getPropertyOrEnv(String envKey, String proKey) {

plugin/src/test/java/io/jenkins/plugins/casc/yaml/CustomMergeStrategyTest.java

@@ -0,0 +1,70 @@
+package io.jenkins.plugins.casc.yaml;
+
+import static io.jenkins.plugins.casc.ConfigurationContext.CASC_MERGE_STRATEGY_ENV;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertThrows;
+
+import io.jenkins.plugins.casc.ConfigurationContext;
+import io.jenkins.plugins.casc.ConfiguratorException;
+import io.jenkins.plugins.casc.ConfiguratorRegistry;
+import java.util.List;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.contrib.java.lang.system.EnvironmentVariables;
+import org.jvnet.hudson.test.JenkinsSessionRule;
+import org.jvnet.hudson.test.TestExtension;
+import org.yaml.snakeyaml.nodes.Node;
+
+public class CustomMergeStrategyTest {
+
+    @Rule
+    public JenkinsSessionRule session = new JenkinsSessionRule();
+
+    @Rule
+    public final EnvironmentVariables environment = new EnvironmentVariables();
+
+    @Test
+    public void customMergeStrategy_withoutEnvironment() throws Throwable {
+        session.then(r -> {
+            assertThat(System.getenv(CASC_MERGE_STRATEGY_ENV), nullValue());
+            customMergeStrategy();
+        });
+    }
+
+    @Test
+    public void customMergeStrategy_withEnvironment() throws Throwable {
+        environment.set(CASC_MERGE_STRATEGY_ENV, "override");
+        session.then(r -> {
+            assertThat(System.getenv(CASC_MERGE_STRATEGY_ENV), is("override"));
+            customMergeStrategy();
+        });
+    }
+
+    private void customMergeStrategy() {
+        ConfiguratorRegistry registry = ConfiguratorRegistry.get();
+        ConfigurationContext customContext = new ConfigurationContext(registry, "custom-test");
+        String normalSource = getClass().getResource("normal.yml").toExternalForm();
+        String overwriteSource = getClass().getResource("overwrite.yml").toExternalForm();
+
+        List<YamlSource> list = List.of(YamlSource.of(normalSource), YamlSource.of(overwriteSource));
+
+        ConfiguratorException exception =
+                assertThrows(ConfiguratorException.class, () -> YamlUtils.merge(list, customContext));
+        assertThat(exception.getMessage(), is("custom-test merge strategy"));
+    }
+
+    @TestExtension
+    public static class CustomTestMergeStrategy implements MergeStrategy {
+        @Override
+        public void merge(Node firstNode, Node secondNode, String source) throws ConfiguratorException {
+            throw new ConfiguratorException("custom-test merge strategy");
+        }
+
+        @Override
+        public String getName() {
+            return "custom-test";
+        }
+    }
+}