Improve documentation and test coverage.

src/main/java/ch/njol/skript/structures/StructUsing.java

@@ -62,6 +62,9 @@ public boolean init(Literal<?> @NotNull [] arguments, int pattern, ParseResult r
 	private void enableExperiment(String name) {
 		this.experiment = Skript.experiments().find(name.trim());
 		switch (experiment.phase()) {
+			case MAINSTREAM:
+				Skript.warning("The experimental feature '" + name + "' is now included by default and is no longer required.");
+				break;
 			case DEPRECATED:
 				Skript.warning("The experimental feature '" + name + "' is deprecated and may be removed in future versions.");
 				break;

src/main/java/ch/njol/skript/test/runner/TestFeatures.java

@@ -31,6 +31,7 @@
  */
 public enum TestFeatures implements Experiment {
 	EXAMPLE_FEATURE("example feature", LifeCycle.STABLE),
+	DEPRECATED_FEATURE("deprecated feature", LifeCycle.DEPRECATED),
 	TEST_FEATURE("test", LifeCycle.EXPERIMENTAL, "test[ing]", "fizz[ ]buzz")
 	;
 

src/main/java/org/skriptlang/skript/lang/experiment/Experiment.java

@@ -20,6 +20,7 @@
 
 import ch.njol.skript.patterns.PatternCompiler;
 import ch.njol.skript.patterns.SkriptPattern;
+import org.jetbrains.annotations.ApiStatus;
 
 import java.util.Objects;
 
@@ -31,10 +32,22 @@
  */
 public interface Experiment {
 
+	@ApiStatus.Internal
 	static Experiment unknown(String text) {
 		return new UnmatchedExperiment(text);
 	}
 
+	/**
+	 * A constant experiment provider (designed for the use of addons).
+	 * @param codeName The debug 'code name' of this feature.
+	 * @param phase The stability of this feature.
+	 * @param patterns What the user may write to match the feature. Defaults to the codename if not set.
+	 * @return An experiment flag.
+	 */
+	static Experiment constant(String codeName, LifeCycle phase, String... patterns) {
+		return new ConstantExperiment(codeName, phase, patterns);
+	}
+
 	/**
 	 * @return The patterns that can be written in the `using` structure.
 	 */
@@ -71,21 +84,36 @@ default boolean matches(String text) {
 }
 
 /**
- * The dummy class for an unmatched experiment.
- * This is something that was 'used' by a file but was never registered with Skript.
- * These are kept so that they *can* be tested for (e.g. by a third-party extension that uses a post-registration
- * experiment system).
+ * A class for constant experiments.
  */
-class UnmatchedExperiment implements Experiment {
+class ConstantExperiment implements Experiment {
 
 	private final String codeName;
 	private final String[] patterns;
 	private final SkriptPattern compiledPattern;
+	private final LifeCycle phase;
 
-	UnmatchedExperiment(String codeName) {
+	ConstantExperiment(String codeName, LifeCycle phase) {
+		this(codeName, phase, new String[0]);
+	}
+
+	ConstantExperiment(String codeName, LifeCycle phase, String... patterns) {
 		this.codeName = codeName;
-		this.patterns = new String[] {codeName};
-		this.compiledPattern = PatternCompiler.compile(codeName);
+		this.phase = phase;
+		switch (patterns.length) {
+			case 0:
+				this.patterns = new String[]{codeName};
+				this.compiledPattern = PatternCompiler.compile(codeName);
+				break;
+			case 1:
+				this.patterns = patterns;
+				this.compiledPattern = PatternCompiler.compile(patterns[0]);
+				break;
+			default:
+				this.patterns = patterns;
+				this.compiledPattern = PatternCompiler.compile('(' + String.join("|", patterns) + ')');
+				break;
+		}
 	}
 
 	@Override
@@ -100,19 +128,14 @@ public String[] patterns() {
 
 	@Override
 	public LifeCycle phase() {
-		return LifeCycle.UNKNOWN;
+		return phase;
 	}
 
 	@Override
 	public SkriptPattern compiledPattern() {
 		return compiledPattern;
 	}
 
-	@Override
-	public boolean isKnown() {
-		return false;
-	}
-
 	@Override
 	public boolean matches(String text) {
 		return codeName.equals(text);
@@ -132,3 +155,27 @@ public int hashCode() {
 	}
 
 }
+
+/**
+ * The dummy class for an unmatched experiment.
+ * This is something that was 'used' by a file but was never registered with Skript.
+ * These are kept so that they *can* be tested for (e.g. by a third-party extension that uses a post-registration
+ * experiment system).
+ */
+class UnmatchedExperiment extends ConstantExperiment {
+
+	UnmatchedExperiment(String codeName) {
+		super(codeName, LifeCycle.UNKNOWN);
+	}
+
+	@Override
+	public LifeCycle phase() {
+		return LifeCycle.UNKNOWN;
+	}
+
+	@Override
+	public boolean isKnown() {
+		return false;
+	}
+
+}

src/main/java/org/skriptlang/skript/lang/experiment/ExperimentManager.java

@@ -20,6 +20,7 @@
 
 import ch.njol.skript.Skript;
 import ch.njol.skript.SkriptAddon;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.LinkedHashSet;
 import java.util.Set;
@@ -29,7 +30,7 @@
  *
  * @author moderocky
  */
-public class ExperimentManager {
+public class ExperimentManager implements Experimented {
 
 	private final Skript skript;
 	private final Set<Experiment> experiments;
@@ -39,7 +40,12 @@ public ExperimentManager(Skript skript) {
 		this.experiments = new LinkedHashSet<>();
 	}
 
-	public Experiment find(String text) {
+	/**
+	 * Finds an experiment matching this name. If none exist, an 'unknown' one will be created.
+	 * @param text The text provided by the user.
+	 * @return An experiment.
+	 */
+	public @NotNull Experiment find(String text) {
 		if (experiments.isEmpty())
 			return Experiment.unknown(text);
 		for (Experiment experiment : experiments) {
@@ -48,6 +54,9 @@ public Experiment find(String text) {
 		return Experiment.unknown(text);
 	}
 
+	/**
+	 * @return All currently-registered experiments.
+	 */
 	public Experiment[] registered() {
 		return experiments.toArray(new Experiment[0]);
 	}
@@ -63,4 +72,14 @@ public void register(SkriptAddon addon, Experiment experiment) {
 		this.experiments.add(experiment);
 	}
 
+	@Override
+	public boolean hasExperiment(Experiment experiment) {
+		return experiments.contains(experiment);
+	}
+
+	@Override
+	public boolean hasExperiment(String featureName) {
+		return this.find(featureName).isKnown();
+	}
+
 }

src/main/java/org/skriptlang/skript/lang/experiment/Experimented.java

@@ -23,7 +23,7 @@
 /**
  * Something that can have experimental features enabled for.
  * The only intended implementation of this is the {@link org.skriptlang.skript.lang.script.Script},
- * however it is left open for configuration files, etc. that may use this functionality in future.
+ * however it is left open for configuration files, etc. that may use this functionality in the future.
  *
  * @author moderocky
  */
@@ -41,7 +41,7 @@ public interface Experimented {
 	 * @return Whether this has a feature with the given name.
 	 */
 	default boolean hasExperiment(String featureName) {
-		return this.hasExperiment(Skript.experiments().find(featureName));
+		return Skript.experiments().find(featureName).isKnown();
 	}
 
 }

src/main/java/org/skriptlang/skript/lang/experiment/LifeCycle.java

@@ -39,6 +39,13 @@ public enum LifeCycle {
 	 * Scripts will report a deprecation warning on load if a deprecated feature is used.
 	 */
 	DEPRECATED(true),
+	/**
+	 * Represents a feature that was previously opt-in (or experimental) but is now a part of the default set.
+	 * I.e. it no longer needs to be enabled using a feature flag.
+	 * This will provide a little note to the user on load informing them they no longer need to
+	 * use this feature flag.
+	 */
+	MAINSTREAM(true),
 	/**
 	 * Represents an unregistered, unknown feature.
 	 * This occurs when a user tags a script as {@code using X}, where {@code X} is not a registered

src/test/skript/tests/syntaxes/structures/StructUsing.sk

@@ -1,5 +1,6 @@
 using example feature
 using fizz buzz
+using deprecated feature
 
 test "using":
 	assert the current script is using "example feature" with "using feature failed"