Throw ParseException for unsupported character in SpEL expression

Prior to this commit, the SpEL Tokenizer threw an IllegalStateException
when an unsupported character was detected in a SpEL expression;
however, the Javadoc for ExpressionParser.parseExpression() states that
it throws a ParseException if an exception occurred during parsing.

This commit addresses that issue by throwing a SpelParseException for
an unsupported character in a SpEL expression, using a new
UNSUPPORTED_CHARACTER enum constant in SpelMessage.

Closes gh-33767

spring-expression/src/main/java/org/springframework/expression/spel/SpelMessage.java

@@ -291,7 +291,11 @@ public enum SpelMessage {
 
 	/** @since 6.0.13 */
 	NEGATIVE_REPEATED_TEXT_COUNT(Kind.ERROR, 1081,
-			"Repeat count ''{0}'' must not be negative");
+			"Repeat count ''{0}'' must not be negative"),
+
+	/** @since 6.1.15 */
+	UNSUPPORTED_CHARACTER(Kind.ERROR, 1082,
+			"Unsupported character ''{0}'' ({1}) encountered in expression");
 
 
 	private final Kind kind;

spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java

@@ -266,9 +266,7 @@ else if (isTwoCharToken(TokenKind.SAFE_NAVI)) {
 						raiseParseException(this.pos, SpelMessage.UNEXPECTED_ESCAPE_CHAR);
 						break;
 					default:
-						throw new IllegalStateException(
-								"Unsupported character '%s' (%d) encountered at position %d in expression."
-										.formatted(ch, (int) ch, (this.pos + 1)));
+						raiseParseException(this.pos + 1, SpelMessage.UNSUPPORTED_CHARACTER, ch, (int) ch);
 				}
 			}
 		}

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

@@ -42,7 +42,7 @@ public abstract class AbstractExpressionTests {
 	protected static final boolean SHOULD_NOT_BE_WRITABLE = false;
 
 
-	protected final ExpressionParser parser = new SpelExpressionParser();
+	protected final SpelExpressionParser parser = new SpelExpressionParser();
 
 	protected final StandardEvaluationContext context = TestScenarioCreator.getTestEvaluationContext();
 

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

@@ -18,12 +18,12 @@
 
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 import org.springframework.expression.spel.standard.SpelExpression;
-import org.springframework.expression.spel.standard.SpelExpressionParser;
 
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
  * Parse some expressions and check we get the AST we expect.
@@ -34,10 +34,7 @@
  * @author Andy Clement
  * @author Sam Brannen
  */
-class ParsingTests {
-
-	private final SpelExpressionParser parser = new SpelExpressionParser();
-
+class ParsingTests extends AbstractExpressionTests {
 
 	@Nested
 	class Miscellaneous {
@@ -104,12 +101,14 @@ void supportedCharactersInIdentifiers() {
 			parseCheck("have乐趣()");
 		}
 
-		@Test
-		void unsupportedCharactersInIdentifiers() {
-			// Invalid syntax
-			assertThatIllegalStateException()
-					.isThrownBy(() -> parser.parseRaw("apple~banana"))
-					.withMessage("Unsupported character '~' (126) encountered at position 6 in expression.");
+		@ParameterizedTest(name = "expression = ''{0}''")
+		@CsvSource(textBlock = """
+			apple~banana, ~, 6
+			map[‘c],      ‘, 5
+			A § B,        §, 3
+			""")
+		void unsupportedCharacter(String expression, char ch, int position) {
+			parseAndCheckError(expression, SpelMessage.UNSUPPORTED_CHARACTER, position, ch, (int) ch);
 		}
 
 		@Test