feat(settings): add feature flags functionality IQSS#9297

src/main/java/edu/harvard/iq/dataverse/settings/FeatureFlags.java

@@ -0,0 +1,45 @@
+package edu.harvard.iq.dataverse.settings;
+
+/**
+ * <p>
+ *     This enum holds so-called "feature flags" aka "feature gates", etc. It can be used throughout the application
+ *     to avoid activating or using experimental functionality or feature previews that are opt-in.
+ * </p><p>
+ *     The current implementation reuses {@link JvmSettings} to interpret any
+ *     <a href="https://download.eclipse.org/microprofile/microprofile-config-3.0/microprofile-config-spec-3.0.html#_built_in_converters">boolean values</a>
+ *     (true == case-insensitive one of "true", "1", "YES", "Y", "ON") and hook into the usual settings system
+ *     (any MicroProfile Config Source available).
+ * </p><p>
+ *     If you add any new flags, please add it here, think of a default status, add some Javadocs about the flagged
+ *     feature and add a "@since" tag to make it easier to identify when a flag has been introduced.
+ * </p><p>
+ *     When removing a flag because of a feature being removed, drop the entry. When a feature matures, drop the flag,
+ *     too! Flags are not meant to be switches for configuration!
+ * </p>
+ *
+ * @see <a href="https://guides.dataverse.org/en/latest/installation/config.html#feature-flags">Configuration Guide</a>
+ * @see <a href="https://guides.dataverse.org/en/latest/developers/configuration.html#adding-a-feature-flag">Developer Guide</a>
+ */
+public enum FeatureFlags {
+
+    /* None yet - please add the first here. Example code:
+     *
+     * MY_FLAG_NAME_HERE("sth-fancy", false),
+     *
+     */
+
+    ;
+
+    final String flag;
+    final boolean defaultStatus;
+
+    FeatureFlags(String flag, boolean defaultStatus) {
+        this.flag = flag;
+        this.defaultStatus = defaultStatus;
+    }
+
+    public boolean enabled() {
+        return JvmSettings.FEATURE_FLAG.lookupOptional(Boolean.class, flag).orElse(defaultStatus);
+    }
+
+}

src/main/java/edu/harvard/iq/dataverse/settings/JvmSettings.java

@@ -64,6 +64,10 @@ public enum JvmSettings {
     SCOPE_API(PREFIX, "api"),
     API_SIGNING_SECRET(SCOPE_API, "signing-secret"),
 
+    // FEATURE FLAGS SETTINGS
+    SCOPE_FLAGS(PREFIX, "feature"),
+    FEATURE_FLAG(SCOPE_FLAGS), // this is a placeholder, to be filled in by FeatureFlag entries
+
     ;
 
     private static final String SCOPE_SEPARATOR = ".";