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<h2>CodeNarc - Creating a Rule<a name="CodeNarc_-_Creating_a_Rule"></a></h2><!-- ~~~~~~~~~~~~~~~~~~~~~~~~~ -->
<p><b>CodeNarc</b> includes many predefined rules, but you can also create your own custom rules. See the site navigation menu for a list of rules provided out of the box by <b>CodeNarc</b>. <b>CodeNarc</b> provides abstract superclasses and helper classes for creating new rules.</p>
<p>See this <a class="externalLink" href="http://www.youtube.com/watch?v=ZPu8FaZZwRw">screencast</a> showing how easy it is to create a new rule.</p>
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<h3>The Rule Interface<a name="The_Rule_Interface"></a></h3><!-- ~~~~~~~~~~~~~~~~~~~ -->
<p>All rules must implement the <tt>org.codenarc.rule.Rule</tt> interface. This interface specifies that all rules must define a <i>name</i>, a <i>priority</i> (from 1 to 3), and also implement the <tt>List applyTo(SourceCode sourceCode)</tt> method. The method returns the <i>List</i> of <tt>Violation</tt> objects that result from applying the rule to a single source file.</p></div>
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<h3>The AbstractRule Class<a name="The_AbstractRule_Class"></a></h3><!-- ~~~~~~~~~~~~~~~~~~~~~~~ -->
<p>The <tt>org.codenarc.rule.AbstractRule</tt> class is the abstract superclass (or ancestor) for all rules provided with <b>CodeNarc</b>. It provides many standard properties and helper methods for subclasses, as described in <a href="./codenarc-configuring-rules.html#Standard_Properties_for_Configuring_Rules"> Standard Properties for Configuring Rules</a>.</p>
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<h4><a name="A_Sample_Rule_Subclass_of_AbstractRule">A Sample Rule Subclass of AbstractRule</a></h4><!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
<p>Here is an example rule class that is a subclass of <tt>AbstractRule</tt>:</p>
<div class="source">
<pre>import org.codenarc.rule.AbstractRule
import org.codenarc.source.SourceCode
/**
* Sample rule. Checks for static fields.
*/
class MyStaticFieldRule extends AbstractRule {
String name = 'MyStaticField'
int priority = 2
void applyTo(SourceCode sourceCode, List violations) {
sourceCode.ast.classes.each { clazz ->
clazz.fields.each { fieldNode ->
if (fieldNode.static) {
violations << createViolation(sourceCode, fieldNode)
}
}
}
}
}
</pre></div>
<p>Things to note about <tt>MyStaticFieldRule</tt> class:</p>
<ul>
<li>It extends <tt>AbstractRule</tt>.</li>
<li>It provides <i>name</i> and <i>priority</i> properties as mandated by the <tt>Rule</tt> interface.</li>
<li>It implements the <tt>void applyTo(SourceCode sourceCode, List violations)</tt> method which is declared <i>abstract</i> in the <tt>AbstractRule</tt> superclass.</li>
<li>It accesses the AST for the source code, which is an instance of the <tt>org.codehaus.groovy.ast.ModuleNode</tt> class from Groovy.</li>
<li>It uses the <tt>createViolation()</tt> helper method from <tt>AbstractRule</tt>.</li></ul>
<p>See the <b>CodeNarc</b> source code for other examples (look for rule classes that are direct subclasses of <tt>AbstractRule</tt>).</p></div></div>
<div class="section">
<h3>The AbstractAstVisitorRule and AbstractAstVisitor Classes<a name="The_AbstractAstVisitorRule_and_AbstractAstVisitor_Classes"></a></h3><!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
<p>Many of the rules included with <b>CodeNarc</b> are implemented using the <i>Visitor</i> pattern, as supported by the Groovy AST (Abstract Syntax Tree). See the <tt>ClassCodeVisitorSupport</tt> class within the Groovy distribution (<a class="externalLink" href="http://groovy.codehaus.org/api/index.html">Javadocs</a>).</p>
<div class="section">
<h4>A Sample Rule Using AbstractAstVisitorRule and AbstractAstVisitor<a name="A_Sample_Rule_Using_AbstractAstVisitorRule_and_AbstractAstVisitor"></a></h4><!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
<p>Here is an example rule class that is a subclass of <tt>AbstractAstVisitorRule</tt> that uses an associated AST <i>Visitor</i> class that is a subclass of <tt>AbstractAstVisitor</tt>. This is the code for the <b>EmptyTryBlock</b> rule included with <b>CodeNarc</b>.</p>
<div class="source">
<pre>import org.codenarc.rule.AbstractAstVisitor
import org.codenarc.rule.AbstractAstVisitorRule
import org.codehaus.groovy.ast.stmt.TryCatchStatement
import org.codenarc.util.AstUtil
class EmptyTryBlockRule extends AbstractAstVisitorRule {
String name = 'EmptyTryBlock'
int priority = 2
Class astVisitorClass = EmptyTryBlockAstVisitor
}
class EmptyTryBlockAstVisitor extends AbstractAstVisitor {
void visitTryCatchFinally(TryCatchStatement tryCatchStatement) {
if (AstUtil.isEmptyBlock(tryCatchStatement.tryStatement)) {
addViolation(tryCatchStatement)
}
super.visitTryCatchFinally(tryCatchStatement)
}
}
</pre></div>
<p>Things to note about this example:</p>
<ul>
<li>This file contains two classes. The <tt>EmptyTryBlockRule</tt> class extends <tt>AbstractAstVisitorRule</tt>. The <tt>EmptyTryBlockAstVisitor</tt> extends <tt>AbstractAstVisitor</tt>.</li>
<li><tt>EmptyTryBlockRule</tt> includes an <i>astVisitorClass</i> property that specifies that it uses the <tt>EmptyTryBlockAstVisitor</tt> class.</li>
<li><tt>EmptyTryBlockAstVisitor</tt> implements the <tt>void visitTryCatchFinally(TryCatchStatement)</tt> <i>visitor</i> method defined by the <tt>ClassCodeVisitorSupport</tt> so that it will <i>visit</i> every try/catch statement within the source code.</li>
<li>It uses the <tt>AstUtil</tt> utility class.</li></ul>
<p>See the <b>CodeNarc</b> source code and javadocs for more information and further examples.</p></div></div>
<div class="section">
<h3>Creating a Rule Script<a name="Creating_a_Rule_Script"></a></h3><!-- ~~~~~~~~~~~~~~~~~~~~~~~ -->
<p>You can also create a new rule using a Groovy script file (typically a .groovy file). The script must still define a class that implements the <tt>org.codenarc.rule.Rule</tt> interface.</p>
<p>The main advantage is that the rule does not have to be compiled into a <b>.class</b> file first, so you can avoid the compile/build phase, and its associated hassles. The Groovy script file is parsed (and compiled) at runtime.</p>
<div class="section">
<h4>A Sample Rule Script<a name="A_Sample_Rule_Script"></a></h4><!-- ~~~~~~~~~~~~~~~~~~~~~~ -->
<p>Here is an example rule script. Note that this is the same source code as in the sample rule class shown <a href="#A_Sample_Rule_Subclass_of_AbstractRule">above</a>.</p>
<div class="source">
<pre>import org.codenarc.rule.AbstractRule
import org.codenarc.source.SourceCode
/**
* Sample rule script. Checks for static fields.
*/
class MyStaticFieldRule extends AbstractRule {
String name = 'MyStaticField'
int priority = 2
void applyTo(SourceCode sourceCode, List violations) {
sourceCode.ast.classes.each { clazz ->
clazz.fields.each { fieldNode ->
if (fieldNode.static) {
violations << createViolation(sourceCode, fieldNode)
}
}
}
}
}
</pre></div></div></div></div>
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