Improve diagnostics in SpEL for repeated text

Attempting to create repeated text in a SpEL expression using the
repeat operator can result in errors that are not very helpful to the
user.

This commit improves the diagnostics in SpEL for the repeat operator by
throwing a SpelEvaluationException with a meaningful error message in
order to better assist the user.

Closes gh-30142

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

@@ -21,10 +21,12 @@ import java.math.BigInteger;
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.expression.Expression;
 import org.springframework.expression.spel.ast.Operator;
 import org.springframework.expression.spel.standard.SpelExpression;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.expression.spel.SpelMessage.MAX_REPEATED_TEXT_SIZE_EXCEEDED;
 
 /**
  * Tests the evaluation of expressions using various operators.
@@ -326,11 +328,6 @@ class OperatorTests extends AbstractExpressionTests {
 		evaluate("3.5", 3.5d, Double.class);
 	}
 
-	@Test
-	void multiplyStringInt() {
-		evaluate("'a' * 5", "aaaaa", String.class);
-	}
-
 	@Test
 	void multiplyDoubleDoubleGivesDouble() {
 		evaluate("3.0d * 5.0d", 15.0d, Double.class);
@@ -578,6 +575,19 @@ class OperatorTests extends AbstractExpressionTests {
 		evaluate("'abc' != 'def'", true, Boolean.class);
 	}
 
+	@Test
+	void stringRepeat() {
+		evaluate("'abc' * 0", "", String.class);
+		evaluate("'abc' * 1", "abc", String.class);
+		evaluate("'abc' * 2", "abcabc", String.class);
+
+		Expression expr = parser.parseExpression("'a' * 256");
+		assertThat(expr.getValue(context, String.class)).hasSize(256);
+
+		// 4 is the position of the '*' (repeat operator)
+		evaluateAndCheckError("'a' * 257", String.class, MAX_REPEATED_TEXT_SIZE_EXCEEDED, 4);
+	}
+
 	@Test
 	void longs() {
 		evaluate("3L == 4L", false, Boolean.class);