Evaluate char literals in pipeline rules (#24295)

* evaluate char literals in pipeline rules

* CL

---------

Co-authored-by: Maxwell <98284293+kodjo-anipah@users.noreply.github.com>

changelog/unreleased/issue-24247.toml

@@ -0,0 +1,5 @@
+type = "f"
+message = "Honor character literals in pipeline rules."
+
+pulls = ["24295"]
+issues = ["24247"]

graylog2-server/src/main/java/org/graylog/plugins/pipelineprocessor/parser/PipelineRuleParser.java

@@ -511,10 +511,18 @@ public class PipelineRuleParser {
             exprs.put(ctx, expr);
         }
 
+        /**
+         * Handle chars like strings.
+         * There is no dedicated char type for Graylog rules and, strictly speaking, we should error out. But we have
+         * been silently allowing (and ignoring) chars for 10 years.To not break existing rules, we continue to allow
+         * them. Except now we actually honor the expression value.
+         */
         @Override
         public void exitChar(RuleLangParser.CharContext ctx) {
-            // TODO
-            super.exitChar(ctx);
+            final String text = unescape(unquote(ctx.getText(), '\''));
+            final StringExpression expr = new StringExpression(ctx.getStart(), text);
+            log.trace("CHAR: ctx {} => {}", ctx, expr);
+            exprs.put(ctx, expr);
         }
 
         @Override

graylog2-server/src/test/java/org/graylog/plugins/pipelineprocessor/parser/PipelineRuleParserTest.java

@@ -266,6 +266,16 @@ class PipelineRuleParserTest extends BaseParserTest {
         assertTrue(actionsTriggered.get());
     }
 
+    @Test
+    void charLiteral() {
+        final Rule rule = parseRuleWithOptionalCodegen();
+        Message message = messageFactory.createMessage("hello test", "source", DateTime.now(DateTimeZone.UTC));
+        final Message processedMsg = evaluateRule(rule, message);
+
+        assertNotNull(processedMsg);
+        assertEquals("x", processedMsg.getField("x"));
+    }
+
     @Test
     void typedFieldAccess() throws Exception {
         final Rule rule = parseRuleWithOptionalCodegen();

graylog2-server/src/test/resources/org/graylog/plugins/pipelineprocessor/parser/charLiteral.txt

@@ -0,0 +1,6 @@
+rule "char_literal"
+when
+    true
+then
+    set_field(field: "x", value: 'x');
+end