# Extending PMD

Use XPath to define a new rule for PMD to prevent complex code. The rule should detect the use of three or more nested `if` statements in Java programs so it can detect patterns like the following:

```Java
if (...) {
    ...
    if (...) {
        ...
        if (...) {
            ....
        }
    }

}
```
Notice that the nested `if`s may not be direct children of the outer `if`s. They may be written, for example, inside a `for` loop or any other statement.
Write below the XML definition of your rule.

You can find more information on extending PMD in the following link: https://pmd.github.io/latest/pmd_userdocs_extending_writing_rules_intro.html, as well as help for using `pmd-designer` [here](https://gitlab2.istic.univ-rennes1.fr/VV-2025-2026/VV-ISTIC-TP2/-/blob/main/exercises/designer-help.md).

Use your rule with different projects and describe you findings below. See the [instructions](../sujet.md) for suggestions on the projects to use.

## Answer



```xml
<?xml version="1.0" encoding="UTF-8"?>
<ruleset name="Nested If Ruleset"
         xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">
    <description>
        Ruleset pour détecter 3 niveaux (ou plus) de if imbriqués.
    </description>
    <rule name="nestedIfRule"
        language="java"
        message="nested If"
        class="net.sourceforge.pmd.lang.rule.xpath.XPathRule">
        <description>
            Three or more nested `if` !
        </description>
        <priority>3</priority>
        <properties>
            <property
                name="xpath"
                value ="    //IfStatement[
                                descendant::IfStatement[
                                    descendant::IfStatement
                                ]
                            ]"
            />
        </properties>
    </rule>
</ruleset>
```

en testant un programme Java, il détecte bien les imbrications de 'if' même s'ils ne sont pas directement imbriqués, séparés par un while par exemple