prevent adding two dates at parse time

attempting to add (not subtract) two dates raises an InvalidOperation parse error because there aren't any sane semantics for doing so
while subtraction gives the duration between the dates, there's hardly any good reason to add them

plugin/src/main/java/org/graylog/plugins/pipelineprocessor/parser/PipelineRuleParser.java

@@ -77,6 +77,7 @@
 import org.graylog.plugins.pipelineprocessor.parser.errors.IncompatibleType;
 import org.graylog.plugins.pipelineprocessor.parser.errors.IncompatibleTypes;
 import org.graylog.plugins.pipelineprocessor.parser.errors.InvalidFunctionArgument;
+import org.graylog.plugins.pipelineprocessor.parser.errors.InvalidOperation;
 import org.graylog.plugins.pipelineprocessor.parser.errors.MissingRequiredParam;
 import org.graylog.plugins.pipelineprocessor.parser.errors.NonIndexableType;
 import org.graylog.plugins.pipelineprocessor.parser.errors.OptionalParametersMustBeNamed;
@@ -748,16 +749,21 @@ public void exitComparison(RuleLangParser.ComparisonContext ctx) {
 
         @Override
         public void exitAddition(RuleLangParser.AdditionContext ctx) {
-            final BinaryExpression binaryExpr = (BinaryExpression) parseContext.expressions().get(ctx);
-            final Class leftType = binaryExpr.left().getType();
-            final Class rightType = binaryExpr.right().getType();
+            final AdditionExpression addExpression = (AdditionExpression) parseContext.expressions().get(ctx);
+            final Class leftType = addExpression.left().getType();
+            final Class rightType = addExpression.right().getType();
 
             // special case for DateTime/Period, which are all compatible
             final boolean leftDate = DateTime.class.equals(leftType);
             final boolean rightDate = DateTime.class.equals(rightType);
             final boolean leftPeriod = Period.class.equals(leftType);
             final boolean rightPeriod = Period.class.equals(rightType);
-            if (leftDate && rightDate || leftDate && rightPeriod || leftPeriod && rightDate || leftPeriod && rightPeriod) {
+            if (leftDate && rightDate) {
+                if (addExpression.isPlus()) {
+                    parseContext.addError(new InvalidOperation(ctx, addExpression, "Unable to add two dates"));
+                }
+                return;
+            } else if (leftDate && rightPeriod || leftPeriod && rightDate || leftPeriod && rightPeriod) {
                 return;
             }
             // otherwise check generic binary expression

plugin/src/main/java/org/graylog/plugins/pipelineprocessor/parser/errors/InvalidOperation.java

@@ -0,0 +1,32 @@
+package org.graylog.plugins.pipelineprocessor.parser.errors;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.graylog.plugins.pipelineprocessor.ast.expressions.Expression;
+
+public class InvalidOperation extends ParseError {
+    private final Expression expr;
+
+    private final String message;
+
+    public InvalidOperation(ParserRuleContext ctx, Expression expr, String message) {
+        super("invalid_operation", ctx);
+        this.expr = expr;
+        this.message = message;
+    }
+
+    @JsonProperty("reason")
+    @Override
+    public String toString() {
+        return "Invalid operation: " + message;
+    }
+
+    public Expression getExpression() {
+        return expr;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+}

plugin/src/test/java/org/graylog/plugins/pipelineprocessor/parser/PipelineRuleParserTest.java

@@ -51,6 +51,7 @@
 import org.graylog.plugins.pipelineprocessor.parser.errors.IncompatibleIndexType;
 import org.graylog.plugins.pipelineprocessor.parser.errors.IncompatibleTypes;
 import org.graylog.plugins.pipelineprocessor.parser.errors.InvalidFunctionArgument;
+import org.graylog.plugins.pipelineprocessor.parser.errors.InvalidOperation;
 import org.graylog.plugins.pipelineprocessor.parser.errors.NonIndexableType;
 import org.graylog.plugins.pipelineprocessor.parser.errors.OptionalParametersMustBeNamed;
 import org.graylog.plugins.pipelineprocessor.parser.errors.ParseError;
@@ -388,6 +389,18 @@ public void dateArithmetic() {
 
     }
 
+    @Test
+    public void invalidDateAddition() {
+        try {
+            parseRuleWithOptionalCodegen();
+            fail("Should have thrown parse exception");
+        } catch (ParseException e) {
+            assertEquals(1, e.getErrors().size());
+            assertEquals(InvalidOperation.class, Iterables.getOnlyElement(e.getErrors()).getClass());
+        }
+    }
+
+
     public static class CustomObject {
         private final String id;
 

plugin/src/test/resources/org/graylog/plugins/pipelineprocessor/parser/invalidDateAddition.txt

@@ -0,0 +1,4 @@
+rule "cannot add dates"
+when
+    now() + now() == now()
+end