adds EvaluationException when accessing an out-of-bounds array index (#490)

Author: uklimaschewski

src/main/java/com/ezylang/evalex/Expression.java

@@ -196,6 +196,14 @@ private EvaluationValue evaluateArrayIndex(ASTNode startNode) throws EvaluationE
     EvaluationValue index = evaluateSubtree(startNode.getParameters().get(1));
 
     if (array.isArrayValue() && index.isNumberValue()) {
+      if (index.getNumberValue().intValue() < 0
+          || index.getNumberValue().intValue() >= array.getArrayValue().size()) {
+        throw new EvaluationException(
+            startNode.getToken(),
+            String.format(
+                "Index %d out of bounds for array of length %d",
+                index.getNumberValue().intValue(), array.getArrayValue().size()));
+      }
       return array.getArrayValue().get(index.getNumberValue().intValue());
     } else {
       throw EvaluationException.ofUnsupportedDataTypeInOperation(startNode.getToken());

src/main/java/com/ezylang/evalex/parser/Tokenizer.java

@@ -312,6 +312,7 @@ private boolean prefixOperatorAllowed() {
       case INFIX_OPERATOR:
       case COMMA:
       case PREFIX_OPERATOR:
+      case ARRAY_OPEN:
         return true;
       default:
         return false;

src/test/java/com/ezylang/evalex/ExpressionEvaluatorArrayTest.java

@@ -151,4 +151,26 @@ void testThrowsUnsupportedDataTypeForIndex() {
         .isInstanceOf(EvaluationException.class)
         .hasMessage("Unsupported data types in operation");
   }
+
+  @Test
+  void testArrayIndexOutOfBounds() {
+    assertThatThrownBy(
+            () -> {
+              List<?> array = List.of("Hello");
+              createExpression("a[1]").with("a", array).evaluate();
+            })
+        .isInstanceOf(EvaluationException.class)
+        .hasMessage("Index 1 out of bounds for array of length 1");
+  }
+
+  @Test
+  void testArrayNegativeIndex() {
+    assertThatThrownBy(
+            () -> {
+              List<?> array = List.of("Hello");
+              createExpression("a[-1]").with("a", array).evaluate();
+            })
+        .isInstanceOf(EvaluationException.class)
+        .hasMessage("Index -1 out of bounds for array of length 1");
+  }
 }