UndefinedVariable does not contain externalInfoUrl in output

[yykamei]

• PHPMD version: 2.8.1
• PHP Version: 7.4.1
• Installation type: composer
• Operating System / Distribution & Version: Debian Buster

Current Behavior

The violation UndefinedVariable does not contain externalInfoUrl in its element like this:

<pmd version="@project.version@" timestamp="2020-01-08T10:31:06+00:00">
  <file name="/tmp/test.php">
    <violation beginline="3" endline="3" rule="UndefinedVariable" ruleset="Clean Code Rules" priority="3">
      Avoid using undefined variables such as '$x' which will lead to PHP notices.
    </violation>
  </file>
</pmd>

Expected Behavior

I expect the output below:

<?xml version="1.0" encoding="UTF-8" ?>
<pmd version="@project.version@" timestamp="2020-01-08T10:31:15+00:00">
  <file name="/tmp/test.php">
    <violation beginline="3" endline="3" rule="UndefinedVariable" ruleset="Clean Code Rules" externalInfoUrl="https://phpmd.org/rules/cleancode.html#undefinedvariable" priority="3">
      Avoid using undefined variables such as '$x' which will lead to PHP notices.
    </violation>
  </file>
</pmd>

Steps To Reproduce:

Prepare the file test.php:

<?php
function printX() {
    echo $x;
}

And, then run the following command:

$ phpmd test.php xml cleancode

Checks before submitting

• Be sure that there isn't already an issue about this. See: Issues list
• Be sure that there isn't already a pull request about this. See: Pull requests
• I have added every step to reproduce the bug.
• If possible I added relevant code examples.
• This issue is about 1 bug and nothing more.
• The issue has a descriptive title. For example: "JSON rendering failed on Windows for filenames with space".

---

I think the following patch resolves the issue, but I'm not sure this exactly works.

diff --git a/src/main/resources/rulesets/cleancode.xml b/src/main/resources/rulesets/cleancode.xml
index 3f01727..4a81006 100644
--- a/src/main/resources/rulesets/cleancode.xml
+++ b/src/main/resources/rulesets/cleancode.xml
@@ -182,7 +182,7 @@ function make() {
           since="2.8.0"
           message="Avoid using undefined variables such as '{0}' which will lead to PHP notices."
           class="PHPMD\Rule\CleanCode\UndefinedVariable"
-          externalInfoUrl="">
+          externalInfoUrl="https://phpmd.org/rules/cleancode.html#undefinedvariable">
         <description>
             Detects when a variable is used that has not been defined before.
         </description>