Check for variable referencing order

analyzer/src/main/java/nl/basjes/parse/useragent/analyze/Matcher.java

@@ -229,10 +229,20 @@ public Matcher(Analyzer analyzer,
             }
         }
 
+        // Verify that a variable only contains the variables that have been defined BEFORE it (also not referencing itself).
+        // If all is ok we link them
+        Set<MatcherAction> seenVariables = new HashSet<>(variableActions.size());
         for (MatcherVariableAction variableAction: variableActions) {
+            seenVariables.add(variableAction); // Add myself
             Set<MatcherAction> interestedActions = informMatcherActionsAboutVariables.get(variableAction.getVariableName());
             if (interestedActions != null && !interestedActions.isEmpty()) {
                 variableAction.setInterestedActions(interestedActions);
+                for (MatcherAction interestedAction : interestedActions) {
+                    if (seenVariables.contains(interestedAction)) {
+                        throw new InvalidParserConfigurationException("Syntax error: The line >>" + interestedAction + "<< " +
+                            "is referencing variable @"+variableAction.getVariableName()+ " which is not defined yet.");
+                    }
+                }
             }
         }
 
@@ -399,7 +409,8 @@ public String toString() {
         sb.append("    VARIABLE:\n");
         for (MatcherAction action : dynamicActions) {
             if (action instanceof MatcherVariableAction) {
-                sb.append("        @").append(((MatcherVariableAction) action).getVariableName()).append(":    ").append(action.getMatchExpression()).append("\n");
+                sb.append("        @").append(((MatcherVariableAction) action).getVariableName())
+                    .append(":    ").append(action.getMatchExpression()).append("\n");
                 sb.append("        -->").append(action.getMatches().toStrings()).append("\n");
             }
         }

analyzer/src/test/java/nl/basjes/parse/useragent/TestErrorHandling.java

@@ -114,6 +114,14 @@ public void checkSyntaxErrorExpect() {
         Assert.assertTrue(uaa.runTests(false, false));
     }
 
+    @Test
+    public void checkSyntaxErrorVariableBackReference() {
+        expectedEx.expect(InvalidParserConfigurationException.class);
+        expectedEx.expectMessage(new StringStartsWith("Syntax error"));
+
+        UserAgentAnalyzerTester uaa = new UserAgentAnalyzerTester("classpath*:BadDefinitions/Variable-BackReference.yaml");
+        Assert.assertTrue(uaa.runTests(false, false));
+    }
 
     @Test
     public void methodInputValidation(){

analyzer/src/test/resources/BadDefinitions/Variable-BackReference.yaml

@@ -0,0 +1,25 @@
+#
+# Yet Another UserAgent Analyzer
+# Copyright (C) 2013-2017 Niels Basjes
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an AS IS BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+config:
+
+- matcher:
+    variable:
+    # This must fail because the ordering of the variables is important: First define; then use
+    - 'VariableOne: NormalizeBrand[@VariableTwo.name]'
+    - 'VariableTwo: agent.product.version="3"^'
+    extract:
+    - 'Dummy : 1: "Dummy"'