Support single String argument for varargs invocations in SpEL

Prior to this commit, the Spring Expression Language (SpEL) incorrectly
split single String arguments by comma for Object... varargs method and
constructor invocations.

This commit addresses this by checking if the single argument type is
already "assignable" to the varargs component type instead of "equal"
to the varargs component type.

Closes gh-33013

spring-expression/src/main/java/org/springframework/expression/spel/support/ReflectionHelper.java

@@ -308,11 +308,11 @@ public abstract class ReflectionHelper {
 						conversionOccurred = true;
 					}
 				}
-				// If the argument type is equal to the varargs component type, there is no need to
+				// If the argument type is assignable to the varargs component type, there is no need to
 				// convert it or wrap it in an array. For example, using StringToArrayConverter to
 				// convert a String containing a comma would result in the String being split and
 				// repackaged in an array when it should be used as-is.
-				else if (!sourceType.equals(componentTypeDesc)) {
+				else if (!sourceType.isAssignableTo(componentTypeDesc)) {
 					arguments[varargsPosition] = converter.convertValue(argument, sourceType, targetType);
 				}
 				// Possible outcomes of the above if-else block:
@@ -384,7 +384,7 @@ public abstract class ReflectionHelper {
 			ResolvableType varArgResolvableType = ResolvableType.forClass(varArgClass);
 			TypeDescriptor varArgComponentType = new TypeDescriptor(varArgResolvableType, varArgClass, null);
 			TypeDescriptor componentTypeDesc = varArgComponentType.getElementTypeDescriptor();
-			// TODO Determine why componentTypeDesc is null.
+			// TODO Determine why componentTypeDesc can be null.
 			// Assert.state(componentTypeDesc != null, "Component type must not be null for a varargs array");
 
 			// If the target is varargs and there is just one more argument, then convert it here.
@@ -398,11 +398,11 @@ public abstract class ReflectionHelper {
 						conversionOccurred = true;
 					}
 				}
-				// If the argument type is equal to the varargs component type, there is no need to
+				// If the argument type is assignable to the varargs component type, there is no need to
 				// convert it or wrap it in an array. For example, using StringToArrayConverter to
 				// convert a String containing a comma would result in the String being split and
 				// repackaged in an array when it should be used as-is.
-				else if (!sourceType.equals(componentTypeDesc)) {
+				else if (componentTypeDesc != null && !sourceType.isAssignableTo(componentTypeDesc)) {
 					arguments[varargsPosition] = converter.convertValue(argument, sourceType, varArgComponentType);
 				}
 				// Possible outcomes of the above if-else block:

spring-expression/src/test/java/org/springframework/expression/spel/MethodInvocationTests.java

@@ -293,6 +293,46 @@ class MethodInvocationTests extends AbstractExpressionTests {
 		evaluate("aVarargsMethod3('foo', 'bar,baz')", "foo-bar,baz", String.class);
 	}
 
+	@Test  // gh-33013
+	void testVarargsWithObjectArrayType() {
+		// Calling 'public String formatObjectVarargs(String format, Object... args)' -> String.format(format, args)
+
+		// No var-args and no conversion necessary
+		evaluate("formatObjectVarargs('x')", "x", String.class);
+
+		// No var-args but conversion necessary
+		evaluate("formatObjectVarargs(9)", "9", String.class);
+
+		// No conversion necessary
+		evaluate("formatObjectVarargs('x -> %s', '')", "x -> ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', ' ')", "x ->  ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', 'a')", "x -> a", String.class);
+		evaluate("formatObjectVarargs('x -> %s %s %s', 'a', 'b', 'c')", "x -> a b c", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new Object[]{''})", "x -> ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new String[]{''})", "x -> ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new Object[]{' '})", "x ->  ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new String[]{' '})", "x ->  ", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new Object[]{'a'})", "x -> a", String.class);
+		evaluate("formatObjectVarargs('x -> %s', new String[]{'a'})", "x -> a", String.class);
+		evaluate("formatObjectVarargs('x -> %s %s %s', new Object[]{'a', 'b', 'c'})", "x -> a b c", String.class);
+		evaluate("formatObjectVarargs('x -> %s %s %s', new String[]{'a', 'b', 'c'})", "x -> a b c", String.class);
+
+		// Conversion necessary
+		evaluate("formatObjectVarargs('x -> %s %s', 2, 3)", "x -> 2 3", String.class);
+		evaluate("formatObjectVarargs('x -> %s %s', 'a', 3.0d)", "x -> a 3.0", String.class);
+
+		// Individual string contains a comma with multiple varargs arguments
+		evaluate("formatObjectVarargs('foo -> %s %s', ',', 'baz')", "foo -> , baz", String.class);
+		evaluate("formatObjectVarargs('foo -> %s %s', 'bar', ',baz')", "foo -> bar ,baz", String.class);
+		evaluate("formatObjectVarargs('foo -> %s %s', 'bar,', 'baz')", "foo -> bar, baz", String.class);
+
+		// Individual string contains a comma with single varargs argument.
+		evaluate("formatObjectVarargs('foo -> %s', ',')", "foo -> ,", String.class);
+		evaluate("formatObjectVarargs('foo -> %s', ',bar')", "foo -> ,bar", String.class);
+		evaluate("formatObjectVarargs('foo -> %s', 'bar,')", "foo -> bar,", String.class);
+		evaluate("formatObjectVarargs('foo -> %s', 'bar,baz')", "foo -> bar,baz", String.class);
+	}
+
 	@Test
 	void testVarargsOptionalInvocation() {
 		// Calling 'public String optionalVarargsMethod(Optional<String>... values)'

spring-expression/src/test/java/org/springframework/expression/spel/SpelReproTests.java

@@ -69,6 +69,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatException;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.assertj.core.api.InstanceOfAssertFactories.list;
 
 /**
  * Reproduction tests cornering various reported SpEL issues.
@@ -1436,13 +1437,20 @@ class SpelReproTests extends AbstractExpressionTests {
 		assertThat(expression.getValue(new NamedUser())).isEqualTo(NamedUser.class.getName());
 	}
 
-	@Test
-	void SPR12522() {
+	@Test  // gh-17127, SPR-12522
+	void arraysAsListWithNoArguments() {
+		SpelExpressionParser parser = new SpelExpressionParser();
+		Expression expression = parser.parseExpression("T(java.util.Arrays).asList()");
+		List<?> value = expression.getValue(List.class);
+		assertThat(value).isEmpty();
+	}
+
+	@Test  // gh-33013
+	void arraysAsListWithSingleEmptyStringArgument() {
 		SpelExpressionParser parser = new SpelExpressionParser();
 		Expression expression = parser.parseExpression("T(java.util.Arrays).asList('')");
-		Object value = expression.getValue();
-		assertThat(value).isInstanceOf(List.class);
-		assertThat(((List<?>) value)).isEmpty();
+		List<?> value = expression.getValue(List.class);
+		assertThat(value).asInstanceOf(list(String.class)).containsExactly("");
 	}
 
 	@Test

spring-expression/src/test/java/org/springframework/expression/spel/TestScenarioCreator.java

@@ -100,7 +100,12 @@ class TestScenarioCreator {
 		MethodHandle messageStaticFullyBound = messageStaticPartiallyBound
 				.bindTo(new String[] { "prerecorded", "3", "Oh Hello World", "ignored"});
 		testContext.registerFunction("messageStaticBound", messageStaticFullyBound);
-	}
+
+		// #formatObjectVarargs(format, args...)
+		MethodHandle formatObjectVarargs = MethodHandles.lookup().findStatic(TestScenarioCreator.class,
+				"formatObjectVarargs", MethodType.methodType(String.class, String.class, Object[].class));
+		testContext.registerFunction("formatObjectVarargs", formatObjectVarargs);
+}
 
 	/**
 	 * Register some variables that can be referenced from the tests
@@ -154,4 +159,8 @@ class TestScenarioCreator {
 		return template.formatted((Object[]) args);
 	}
 
+	public static String formatObjectVarargs(String format, Object... args) {
+		return String.format(format, args);
+	}
+
 }

spring-expression/src/test/java/org/springframework/expression/spel/VariableAndFunctionTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.expression.spel;
 
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.expression.spel.standard.SpelExpressionParser;
@@ -101,6 +102,54 @@ class VariableAndFunctionTests extends AbstractExpressionTests {
 		evaluate("#varargsFunction2(9,'a',null,'b')", "9-[a, null, b]", String.class);
 	}
 
+	@Disabled("Disabled until bugs are reported and fixed")
+	@Test
+	void functionWithVarargsViaMethodHandle_CurrentlyFailing() {
+		// Calling 'public static String formatObjectVarargs(String format, Object... args)' -> String.format(format, args)
+
+		// No var-args and no conversion necessary
+		evaluate("#formatObjectVarargs('x')", "x", String.class);
+
+		// No var-args but conversion necessary
+		evaluate("#formatObjectVarargs(9)", "9", String.class);
+
+		// No conversion necessary
+		evaluate("#formatObjectVarargs('x -> %s', new Object[]{''})", "x -> ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', new String[]{''})", "x -> ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', new Object[]{' '})", "x ->  ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', new String[]{' '})", "x ->  ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', new Object[]{'a'})", "x -> a", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', new String[]{'a'})", "x -> a", String.class);
+		evaluate("#formatObjectVarargs('x -> %s %s %s', new Object[]{'a', 'b', 'c'})", "x -> a b c", String.class);
+		evaluate("#formatObjectVarargs('x -> %s %s %s', new String[]{'a', 'b', 'c'})", "x -> a b c", String.class);
+	}
+
+	@Test  // gh-33013
+	void functionWithVarargsViaMethodHandle() {
+		// Calling 'public static String formatObjectVarargs(String format, Object... args)' -> String.format(format, args)
+
+		// No conversion necessary
+		evaluate("#formatObjectVarargs('x -> %s', '')", "x -> ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', ' ')", "x ->  ", String.class);
+		evaluate("#formatObjectVarargs('x -> %s', 'a')", "x -> a", String.class);
+		evaluate("#formatObjectVarargs('x -> %s %s %s', 'a', 'b', 'c')", "x -> a b c", String.class);
+
+		// Conversion necessary
+		evaluate("#formatObjectVarargs('x -> %s %s', 2, 3)", "x -> 2 3", String.class);
+		evaluate("#formatObjectVarargs('x -> %s %s', 'a', 3.0d)", "x -> a 3.0", String.class);
+
+		// Individual string contains a comma with multiple varargs arguments
+		evaluate("#formatObjectVarargs('foo -> %s %s', ',', 'baz')", "foo -> , baz", String.class);
+		evaluate("#formatObjectVarargs('foo -> %s %s', 'bar', ',baz')", "foo -> bar ,baz", String.class);
+		evaluate("#formatObjectVarargs('foo -> %s %s', 'bar,', 'baz')", "foo -> bar, baz", String.class);
+
+		// Individual string contains a comma with single varargs argument.
+		evaluate("#formatObjectVarargs('foo -> %s', ',')", "foo -> ,", String.class);
+		evaluate("#formatObjectVarargs('foo -> %s', ',bar')", "foo -> ,bar", String.class);
+		evaluate("#formatObjectVarargs('foo -> %s', 'bar,')", "foo -> bar,", String.class);
+		evaluate("#formatObjectVarargs('foo -> %s', 'bar,baz')", "foo -> bar,baz", String.class);
+	}
+
 	@Test
 	void functionMethodMustBeStatic() throws Exception {
 		SpelExpressionParser parser = new SpelExpressionParser();

spring-expression/src/test/java/org/springframework/expression/spel/testresources/Inventor.java

@@ -217,6 +217,11 @@ public class Inventor {
 		return str1 + "-" + String.join("-", strings);
 	}
 
+	public String formatObjectVarargs(String format, Object... args) {
+		return String.format(format, args);
+	}
+
+
 	public Inventor(String... strings) {
 		if (strings.length > 0) {
 			this.name = strings[0];