Null pointer check in assignment statement (#17736)

* change lexer prio for ID

* update CL

* add NPE check and unit test

* revert change to grammar

changelog/unreleased/issue-7006.toml

@@ -0,0 +1,5 @@
+type = "c"
+message = "Flag an error in rule source editor when variable name is a reserved word."
+
+issues = ["7006"]
+pulls = ["17736"]

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

@@ -294,11 +294,13 @@ public void exitFuncStmt(RuleLangParser.FuncStmtContext ctx) {
 
         @Override
         public void exitVarAssignStmt(RuleLangParser.VarAssignStmtContext ctx) {
-            final String name = unquote(ctx.varName.getText(), '`');
-            final Expression expr = exprs.get(ctx.expression());
-            parseContext.defineVar(name, expr);
-            definedVars.add(name);
-            parseContext.statements.add(new VarAssignStatement(name, expr));
+            if (ctx.varName != null) {
+                final String name = unquote(ctx.varName.getText(), '`');
+                final Expression expr = exprs.get(ctx.expression());
+                parseContext.defineVar(name, expr);
+                definedVars.add(name);
+                parseContext.statements.add(new VarAssignStatement(name, expr));
+            }
         }
 
         @Override

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

@@ -396,6 +396,16 @@ public void issue185() {
         }
     }
 
+    @Test
+    public void invalidIdentifier() {
+        try {
+            parseRuleWithOptionalCodegen();
+            fail("Should have thrown parse exception");
+        } catch (ParseException e) {
+            assertEquals(1, e.getErrors().size());
+            assertEquals(SyntaxError.class, Iterables.getOnlyElement(e.getErrors()).getClass());
+        }
+    }
 
     public static class CustomObject {
         private final String id;

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

@@ -0,0 +1,5 @@
+rule "invalid identifier"
+when true
+then
+    let match=1;
+end