Use builder method for Expression return type

src/main/java/ch/njol/skript/Skript.java

@@ -1574,7 +1574,8 @@ public static <E extends Expression<T>, T> void registerExpression(
 		Class<E> expressionType, Class<T> returnType, ExpressionType type, String... patterns
 	) throws IllegalArgumentException {
 		checkAcceptRegistrations();
-		skriptRegistry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionType, returnType)
+		skriptRegistry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionType)
+				.returnType(returnType)
 				.priority(type.priority())
 				.origin(getSyntaxOrigin(JavaPlugin.getProvidingPlugin(expressionType)))
 				.addPatterns(patterns)

src/main/java/ch/njol/skript/expressions/base/EventValueExpression.java

@@ -88,10 +88,11 @@ public class EventValueExpression<T> extends SimpleExpression<T> implements Defa
 	 */
 	@ApiStatus.Experimental
 	public static <T> void register(SyntaxRegistry registry, Class<? extends EventValueExpression<T>> expressionClass, Class<T> type, String pattern) {
-		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass, type)
-			.priority(DEFAULT_PRIORITY)
-			.addPattern("[the] " + pattern)
-			.build()
+		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass)
+				.returnType(type)
+				.priority(DEFAULT_PRIORITY)
+				.addPattern("[the] " + pattern)
+				.build()
 		);
 	}
 

src/main/java/ch/njol/skript/expressions/base/PropertyExpression.java

@@ -65,7 +65,8 @@ public abstract class PropertyExpression<F, T> extends SimpleExpression<T> {
 	 */
 	@ApiStatus.Experimental
 	public static <T> void register(SyntaxRegistry registry, Class<? extends Expression<T>> expressionClass, Class<T> type, String property, String fromType) {
-		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass, type)
+		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass)
+				.returnType(type)
 				.priority(DEFAULT_PRIORITY)
 				.addPatterns(
 						"[the] " + property + " of %" + fromType + "%",
@@ -101,7 +102,8 @@ public static <T> void register(Class<? extends Expression<T>> expressionClass,
 	 */
 	@ApiStatus.Experimental
 	public static <T> void registerDefault(SyntaxRegistry registry, Class<? extends Expression<T>> expressionClass, Class<T> type, String property, String fromType) {
-		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass, type)
+		registry.register(SyntaxRegistry.EXPRESSION, SyntaxInfo.Expression.builder(expressionClass)
+				.returnType(type)
 				.priority(DEFAULT_PRIORITY)
 				.addPatterns(
 						"[the] " + property + " [of %" + fromType + "%]",

src/main/java/org/skriptlang/skript/registration/DefaultSyntaxInfos.java

@@ -37,13 +37,12 @@ interface Expression<E extends ch.njol.skript.lang.Expression<R>, R> extends Syn
 		/**
 		 * Constructs a builder for an expression syntax info.
 		 * @param expressionClass The Expression class the info will represent.
-		 * @return An Expression-specific builder for creating a syntax info representing <code>type</code>.
+		 * @return An Expression-specific builder for creating a syntax info representing <code>expressionClass</code>.
 		 * @param <E> The class providing the implementation of the Expression this info represents.
-		 * @param <R> The type of the return type of the Expression.
 		 */
-		@Contract("_, _ -> new")
-		static <E extends ch.njol.skript.lang.Expression<R>, R> Builder<? extends Builder<?, E, R>, E, R> builder(Class<E> expressionClass, Class<R> returnType) {
-			return new ExpressionImpl.BuilderImpl<>(expressionClass, returnType);
+		@Contract("_ -> new")
+		static <E extends ch.njol.skript.lang.Expression<R>, R> Builder<? extends Builder<?, E, R>, E, R> builder(Class<E> expressionClass) {
+			return new ExpressionImpl.BuilderImpl<>(expressionClass);
 		}
 
 		/**
@@ -53,13 +52,22 @@ static <E extends ch.njol.skript.lang.Expression<R>, R> Builder<? extends Builde
 
 		/**
 		 * An Expression-specific builder is used for constructing a new Expression syntax info.
-		 * @see #builder(Class, Class)
+		 * @see #builder(Class)
 		 * @param <B> The type of builder being used.
 		 * @param <E> The Expression class providing the implementation of the syntax info being built.
 		 * @param <R> The type of the return type of the Expression.
 		 */
 		interface Builder<B extends Builder<B, E, R>, E extends ch.njol.skript.lang.Expression<R>, R> extends SyntaxInfo.Builder<B, E> {
 
+			/**
+			 * Sets the class representing the supertype of all values the Expression may return.
+			 * @param returnType The class to use as the return type.
+			 * @return This builder.
+			 * @see Expression#returnType()
+			 */
+			@Contract("_ -> this")
+			B returnType(Class<R> returnType);
+
 			/**
 			 * {@inheritDoc}
 			 */
@@ -118,7 +126,7 @@ public boolean canBeSection() {
 		/**
 		 * Constructs a builder for a structure syntax info.
 		 * @param structureClass The Structure class the info will represent.
-		 * @return A Structure-specific builder for creating a syntax info representing <code>type</code>.
+		 * @return A Structure-specific builder for creating a syntax info representing <code>structureClass</code>.
 		 * @param <E> The class providing the implementation of the Structure this info represents.
 		 */
 		@Contract("_ -> new")

src/main/java/org/skriptlang/skript/registration/DefaultSyntaxInfosImpl.java

@@ -19,6 +19,7 @@
 package org.skriptlang.skript.registration;
 
 import com.google.common.base.MoreObjects;
+import com.google.common.base.Preconditions;
 import org.jetbrains.annotations.Nullable;
 import org.skriptlang.skript.lang.entry.EntryValidator;
 import org.skriptlang.skript.util.Priority;
@@ -39,9 +40,10 @@ public static class ExpressionImpl<E extends ch.njol.skript.lang.Expression<R>,
 
 		ExpressionImpl(
 			SyntaxOrigin origin, Class<E> type, @Nullable Supplier<E> supplier,
-			Collection<String> patterns, Priority priority, Class<R> returnType
+			Collection<String> patterns, Priority priority, @Nullable Class<R> returnType
 		) {
 			super(origin, type, supplier, patterns, priority);
+			Preconditions.checkArgument(returnType != null, "An expression syntax info must have a return type.");
 			this.returnType = returnType;
 		}
 
@@ -77,15 +79,21 @@ public String toString() {
 		/**
 		 * {@inheritDoc}
 		 */
+		@SuppressWarnings("unchecked")
 		static final class BuilderImpl<B extends Expression.Builder<B, E, R>, E extends ch.njol.skript.lang.Expression<R>, R>
 			extends SyntaxInfoImpl.BuilderImpl<B, E>
 			implements Expression.Builder<B, E, R> {
 
-			private final Class<R> returnType;
+			private @Nullable Class<R> returnType;
 
-			BuilderImpl(Class<E> expressionClass, Class<R> returnType) {
+			BuilderImpl(Class<E> expressionClass) {
 				super(expressionClass);
+			}
+
+			@Override
+			public B returnType(Class<R> returnType) {
 				this.returnType = returnType;
+				return (B) this;
 			}
 
 			public Expression<E, R> build() {