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<h1 class="post-title-main">Spoon Patterns</h1>
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<div class="post-content">
<p>Spoon patterns enable you to find code elements. A Spoon pattern is based on a one or several AST nodes, which represent the code to match, where some parts of the AST are pattern parameters. When a pattern is matched, one can access to the code matched in each pattern parameter.</p>
<p>The main classes of Spoon patterns are those in package <code class="language-plaintext highlighter-rouge">spoon.pattern</code>:</p>
<ul>
<li>classes: PatternBuilder, Pattern, Match, PatternBuilderHelper, PatternParameterConfigurator, InlinedStatementConfigurator</li>
<li>enums: ConflictResolutionMode, Quantifier</li>
</ul>
<p>See also <a href="https://github.com/SpoonLabs/spoon-examples/blob/master/src/main/java/fr/inria/gforge/spoon/analysis/PatternTest.java">examples in project <code class="language-plaintext highlighter-rouge">spoon-examples</code></a></p>
<h3 id="example-usage">Example usage</h3>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nc">Factory</span> <span class="n">spoonFactory</span> <span class="o">=</span> <span class="o">...</span>
<span class="nc">Pattern</span> <span class="n">pattern</span> <span class="o">=</span> <span class="nc">PatternBuilder</span><span class="o">.</span><span class="na">create</span><span class="o">(</span><span class="n">mainClass</span><span class="o">.</span><span class="na">getMethodsByName</span><span class="o">(</span><span class="s">"m1"</span><span class="o">).</span><span class="na">get</span><span class="o">(</span><span class="mi">0</span><span class="o">).</span><span class="na">getBody</span><span class="o">().</span><span class="na">clone</span><span class="o">()).</span><span class="na">configurePatternParameters</span><span class="o">().</span><span class="na">build</span><span class="o">();</span>
<span class="c1">//search for all occurences of the method in the root package</span>
<span class="n">pattern</span><span class="o">.</span><span class="na">forEachMatch</span><span class="o">(</span><span class="n">spoonFactory</span><span class="o">.</span><span class="na">getRootPackage</span><span class="o">(),</span> <span class="o">(</span><span class="nc">Match</span> <span class="n">match</span><span class="o">)</span> <span class="o">-></span> <span class="o">{</span>
<span class="nc">Map</span><span class="o"><</span><span class="nc">String</span><span class="o">,</span> <span class="nc">Object</span><span class="o">></span> <span class="n">parameters</span> <span class="o">=</span> <span class="n">match</span><span class="o">.</span><span class="na">getParametersAsMap</span><span class="o">();</span>
<span class="nc">CtMethod</span><span class="o"><?></span> <span class="n">matchingMethod</span> <span class="o">=</span> <span class="n">match</span><span class="o">.</span><span class="na">getMatchingElement</span><span class="o">(</span><span class="nc">CtMethod</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
<span class="nc">String</span> <span class="n">aNameOfMatchedMethod</span> <span class="o">=</span> <span class="n">parameters</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"methodName"</span><span class="o">);</span>
<span class="o">...</span>
<span class="o">});</span>
</code></pre></div></div>
<h3 id="patternbuilder">PatternBuilder</h3>
<p>To create a Spoon pattern, one must use <code class="language-plaintext highlighter-rouge">PatternBuilder</code>, which takes AST nodes as input, and <em>pattern parameters</em> can be defined.</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// creates pattern from the body of method "matcher1"</span>
<span class="n">elem</span> <span class="o">=</span> <span class="n">mainClass</span><span class="o">.</span><span class="na">getMethodsByName</span><span class="o">(</span><span class="s">"matcher1"</span><span class="o">).</span><span class="na">get</span><span class="o">(</span><span class="mi">0</span><span class="o">).</span><span class="na">getBody</span><span class="o">().</span><span class="na">clone</span><span class="o">()</span>
<span class="nc">Pattern</span> <span class="n">t</span> <span class="o">=</span> <span class="nc">PatternBuilder</span><span class="o">.</span><span class="na">create</span><span class="o">(</span><span class="n">elem</span><span class="o">)</span>
<span class="o">.</span><span class="na">build</span><span class="o">();</span>
</code></pre></div></div>
<p>If you call <code class="language-plaintext highlighter-rouge">configurePatternParameters()</code>, all variables that are declared outside the AST node are automatically declared a pattern parameter.</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Pattern t = PatternBuilder.create(elem)
.configurePatternParameters()
.build();
</code></pre></div></div>
<p>One can also create specific parameters with <code class="language-plaintext highlighter-rouge">.configureParameters(pb -> pb.parameter("name").byXXXX</code> (see below)</p>
<h3 id="pattern">Pattern</h3>
<p>Once a <code class="language-plaintext highlighter-rouge">PatternBuilder</code> returns a <code class="language-plaintext highlighter-rouge">Pattern</code>, the main methods of <code class="language-plaintext highlighter-rouge">Pattern</code> are <code class="language-plaintext highlighter-rouge">getMatches</code> and <code class="language-plaintext highlighter-rouge">forEachMatch</code>.</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>List<Match> matches = pattern.getMatches(ctClass);
</code></pre></div></div>
<h3 id="match">Match</h3>
<p>A <code class="language-plaintext highlighter-rouge">Match</code> represents a match of a pattern on a code element. The main methods are <code class="language-plaintext highlighter-rouge">getMatchingElement</code> and <code class="language-plaintext highlighter-rouge">getMatchingElements</code>.</p>
<h3 id="patternbuilderhelper">PatternBuilderHelper</h3>
<p><code class="language-plaintext highlighter-rouge">PatternBuilderHelper</code> is useful to select AST nodes that would act as pattern. See method to get the body (method <code class="language-plaintext highlighter-rouge">setBodyOfMethod</code>) or the return expression of a method (method <code class="language-plaintext highlighter-rouge">setReturnExpressionOfMethod</code>).</p>
<h3 id="patternparameterconfigurator">PatternParameterConfigurator</h3>
<p>To create pattern parameters, one uses a <code class="language-plaintext highlighter-rouge">PatternParameterConfigurator</code> as a lambda:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">//a pattern model </span>
<span class="kt">void</span> <span class="nf">method</span><span class="o">(</span><span class="nc">String</span> <span class="n">_x_</span><span class="o">)</span> <span class="o">{</span>
<span class="n">zeroOneOrMoreStatements</span><span class="o">();</span>
<span class="nc">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">_x_</span><span class="o">);</span>
<span class="o">}</span>
<span class="c1">//a pattern definition</span>
<span class="nc">Pattern</span> <span class="n">t</span> <span class="o">=</span> <span class="nc">PatternBuilder</span><span class="o">.</span><span class="na">create</span><span class="o">(...</span><span class="na">select</span> <span class="n">pattern</span> <span class="n">model</span><span class="o">...)</span>
<span class="o">.</span><span class="na">configureParameters</span><span class="o">(</span><span class="n">pb</span> <span class="o">-></span>
<span class="c1">// creating a pattern parameter called "firstParamName"</span>
<span class="n">pb</span><span class="o">.</span><span class="na">parameter</span><span class="o">(</span><span class="s">"firstParamName"</span><span class="o">)</span>
<span class="c1">//...select which AST nodes are parameters...</span>
<span class="c1">//e.g. using parameter selector</span>
<span class="o">.</span><span class="na">bySimpleName</span><span class="o">(</span><span class="s">"stmt"</span><span class="o">)</span>
<span class="c1">//... you can define as many parameters as you need...</span>
<span class="c1">// another parameter (all usages of variable "_x_"</span>
<span class="n">pb</span><span class="o">.</span><span class="na">parameter</span><span class="o">(</span><span class="s">"lastParamName"</span><span class="o">).</span><span class="na">byVariable</span><span class="o">(</span><span class="s">"_x_"</span><span class="o">);</span>
<span class="o">)</span>
<span class="o">.</span><span class="na">build</span><span class="o">();</span>
</code></pre></div></div>
<p><code class="language-plaintext highlighter-rouge">ParametersBuilder</code> has many methods to create the perfect pattern parameters, incl:</p>
<ul>
<li><code class="language-plaintext highlighter-rouge">byType(Class|CtTypeReference|String)</code> - all the references to the type defined by Class,
CtTypeReference or qualified name are considered as pattern parameter</li>
<li><code class="language-plaintext highlighter-rouge">byLocalType(CtType<?> searchScope, String localTypeSimpleName)</code> - all the types defined in <code class="language-plaintext highlighter-rouge">searchScope</code>
and having simpleName equal to <code class="language-plaintext highlighter-rouge">localTypeSimpleName</code> are considered as pattern parameter</li>
<li><code class="language-plaintext highlighter-rouge">byVariable(CtVariable|String)</code> - all read/write variable references to CtVariable
or any variable named with the provided simple name are considered as pattern parameter</li>
<li><code class="language-plaintext highlighter-rouge">byInvocation(CtMethod<?> method)</code> - all invocations of <code class="language-plaintext highlighter-rouge">method</code> are considered as pattern parameter</li>
<li><code class="language-plaintext highlighter-rouge">byVariable(CtVariable|String... variableName)</code> - each <code class="language-plaintext highlighter-rouge">variableName</code> is a name of a variable
which references instance of a class with fields. Each such field is considered as pattern parameter.</li>
<li><code class="language-plaintext highlighter-rouge">byFilter(Filter)</code> - any pattern model element, where <code class="language-plaintext highlighter-rouge">Filter.accept(element)</code> returns true is a pattern parameter.</li>
<li><code class="language-plaintext highlighter-rouge">byRole(CtRole role, Filter filter)</code> - the attribute defined by <code class="language-plaintext highlighter-rouge">role</code> of all
pattern model elements, where <code class="language-plaintext highlighter-rouge">Filter.accept(element)</code> returns true is a pattern parameter. It can be used to define a variable on any CtElement attribute. E.g. method modifiers or throwables, …</li>
<li><code class="language-plaintext highlighter-rouge">byString(String name)</code> - all pattern model string attributes whose value is equal to <code class="language-plaintext highlighter-rouge">name</code> are considered as pattern parameter. This can be used to define full name of the methods and fields, etc.</li>
<li><code class="language-plaintext highlighter-rouge">bySubstring(String stringMarker)</code> - all pattern model string attributes whose value contains
whole string or a substring equal to <code class="language-plaintext highlighter-rouge">stringMarker</code>are pattern parameter. Note: only the <code class="language-plaintext highlighter-rouge">stringMarker</code> substring of the string value is substituted, other parts of string/element name are kept unchanged.</li>
<li><code class="language-plaintext highlighter-rouge">byNamedElement(String name)</code> - any CtNamedElement identified by its simple name is a pattern parameter.</li>
<li><code class="language-plaintext highlighter-rouge">byReferenceName(String name)</code> - any CtReference identified by its simple name is a pattern parameter.</li>
</ul>
<p>Any parameter of a pattern can be configured like this:</p>
<ul>
<li><code class="language-plaintext highlighter-rouge">setMinOccurrence(int)</code> - defines minimal number of occurrences of the value of this parameter during <strong>matching</strong>,
which is needed by matcher to accept that value.
<ul>
<li><code class="language-plaintext highlighter-rouge">setMinOccurrence(0)</code> - defines optional parameter</li>
<li><code class="language-plaintext highlighter-rouge">setMinOccurrence(1)</code> - defines mandatory parameter</li>
<li><code class="language-plaintext highlighter-rouge">setMinOccurrence(n)</code> - defines parameter, whose value must be repeated at least n-times</li>
</ul>
</li>
<li><code class="language-plaintext highlighter-rouge">setMaxOccurrence(int)</code> - defines maximal number of occurrences of the value of this parameter during <strong>matching</strong>,
which is accepted by matcher to accept that value.</li>
<li><code class="language-plaintext highlighter-rouge">setMatchingStrategy(Quantifier)</code> - defines how the matching engine behaves when two pattern nodes may accept the same value.
<ul>
<li><code class="language-plaintext highlighter-rouge">Quantifier#GREEDY</code> - Greedy quantifiers are considered “greedy” because they force the matcher to read in, or eat, the entire input prior to attempting the next match.
If the next match attempt (the entire input) fails, the matcher backs off the input by one and tries again,
repeating the process until a match is found or there are no more elements left to back off from.</li>
<li><code class="language-plaintext highlighter-rouge">Quantifier#RELUCTANT</code> - The reluctant quantifier takes the opposite approach: It starts at the beginning of the input,
then reluctantly eat one character at a time looking for a match.
The last thing it tries is the entire input.</li>
<li><code class="language-plaintext highlighter-rouge">Quantifier#POSSESSIVE</code> - The possessive quantifier always eats the entire input string,
trying once (and only once) for a match. Unlike the greedy quantifiers, possessive quantifiers never back off,
even if doing so would allow the overall match to succeed.</li>
</ul>
</li>
<li><code class="language-plaintext highlighter-rouge">setValueType(Class type)</code> - defines a required type of the value. If defined the pattern matched, will match only values which are assigneable from the provided <code class="language-plaintext highlighter-rouge">type</code></li>
<li><code class="language-plaintext highlighter-rouge">matchCondition(Class<T> type, Predicate<T> matchCondition)</code> - defines a <code class="language-plaintext highlighter-rouge">Predicate</code>, whose method <code class="language-plaintext highlighter-rouge">boolean test(T)</code>,
are called by pattern matcher. Template matcher accepts that value only if <code class="language-plaintext highlighter-rouge">test</code> returns true for the value.
The <code class="language-plaintext highlighter-rouge">setValueType(type)</code> is called internally too, so match condition assures both a type of value and condition on value.</li>
<li><code class="language-plaintext highlighter-rouge">setContainerKind(ContainerKind)</code> - defines what container are used to store the value.
<ul>
<li><code class="language-plaintext highlighter-rouge">ContainerKind#SINGLE</code> - only single value is accepted as a parameter value.
It can be e.g. single String or single CtStatement, etc.</li>
<li><code class="language-plaintext highlighter-rouge">ContainerKind#LIST</code> - The values are always stored as <code class="language-plaintext highlighter-rouge">List</code>.</li>
<li><code class="language-plaintext highlighter-rouge">ContainerKind#SET</code> - The values are always stored as <code class="language-plaintext highlighter-rouge">Set</code>.</li>
<li><code class="language-plaintext highlighter-rouge">ContainerKind#MAP</code> - The values are always stored as <code class="language-plaintext highlighter-rouge">Map</code>.</li>
</ul>
</li>
</ul>
<h3 id="inlinedstatementconfigurator">InlinedStatementConfigurator</h3>
<p>It is possible to match inlined code, e.g.:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nc">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="mi">1</span><span class="o">);</span>
<span class="nc">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="mi">2</span><span class="o">);</span>
<span class="nc">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="mi">3</span><span class="o">);</span>
</code></pre></div></div>
<p>can be matched by</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="o">;</span> <span class="n">i</span><span class="o"><</span><span class="n">n</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
<span class="nc">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">n</span><span class="o">);</span>
<span class="o">}</span>
</code></pre></div></div>
<p>One mark code to be matched inlined using method <code class="language-plaintext highlighter-rouge">configureInlineStatements</code>, which receives a InlinedStatementConfigurator as follows:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nc">Pattern</span> <span class="n">t</span> <span class="o">=</span> <span class="nc">PatternBuilder</span><span class="o">.</span><span class="na">create</span><span class="o">(...</span><span class="na">select</span> <span class="n">pattern</span> <span class="n">model</span><span class="o">...)</span>
<span class="c1">//...configure parameters...</span>
<span class="n">configureInlineStatements</span><span class="o">(</span><span class="n">ls</span> <span class="o">-></span>
<span class="c1">//...select to be inlined statements...</span>
<span class="c1">//e.g. by variable name:</span>
<span class="n">ls</span><span class="o">.</span><span class="na">byVariableName</span><span class="o">(</span><span class="s">"intValues"</span><span class="o">)</span>
<span class="o">).</span><span class="na">build</span><span class="o">();</span>
</code></pre></div></div>
<p>The inlining methods are:</p>
<ul>
<li><code class="language-plaintext highlighter-rouge">inlineIfOrForeachReferringTo(String varName)</code> - all CtForEach and CtIf statements
whose expression references variable named <code class="language-plaintext highlighter-rouge">varName</code> are understood as
inline statements</li>
<li><code class="language-plaintext highlighter-rouge">markAsInlined(CtForEach|CtIf)</code> - provided CtForEach or CtIf statement
is understood as inline statement</li>
</ul>
<h3 id="generator">Generator</h3>
<p>All patterns can be used for code generation. The idea is that one calls <code class="language-plaintext highlighter-rouge">#generator()</code> on a pattern object to get a <code class="language-plaintext highlighter-rouge">Generator</code>. This class contains methods that takes as input a map of string, objects where each string key points to a pattern parameter name and each map value contains the element to be put in place of the pattern parameter.</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nc">Pattern</span> <span class="n">t</span> <span class="o">=</span> <span class="o">....</span>
<span class="nc">Generator</span> <span class="n">gen</span> <span class="o">=</span> <span class="n">t</span><span class="o">.</span><span class="na">generator</span><span class="o">();</span>
<span class="c1">// the parameters to bind in the generator</span>
<span class="n">params</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">HashMap</span><span class="o"><>();</span>
<span class="n">params</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="s">"targetType"</span><span class="o">,</span> <span class="n">aTargetType</span><span class="o">.</span><span class="na">getReference</span><span class="o">());</span>
<span class="c1">// see all methods generate in Generator</span>
<span class="nc">List</span><span class="o"><</span><span class="nc">CtMethod</span><span class="o">></span> <span class="n">aMethods</span> <span class="o">=</span> <span class="n">pattern</span><span class="o">.</span><span class="na">generator</span><span class="o">().</span><span class="na">generate</span><span class="o">(</span><span class="n">params</span><span class="o">);</span>
</code></pre></div></div>
<h3 id="notes-on-patterns">Notes on patterns</h3>
<p>The unique feature of Spoon pattern matching is that we are matching on AST trees and not source code text. It means that:</p>
<ul>
<li>source code formatting is ignored. For example:</li>
</ul>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">void</span> <span class="nf">m</span><span class="o">()</span> <span class="o">{}</span>
<span class="c1">//matches with</span>
<span class="kt">void</span> <span class="nf">m</span><span class="o">(){</span>
<span class="o">}</span>
</code></pre></div></div>
<ul>
<li>comments are ignored. For example:</li>
</ul>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">void</span> <span class="nf">m</span><span class="o">()</span> <span class="o">{}</span>
<span class="c1">//matches with</span>
<span class="cm">/**
javadoc is ignored
*/</span>
<span class="cm">/* was public before */</span> <span class="kt">void</span> <span class="nf">m</span><span class="o">(</span><span class="cm">/*this is ignored too*/</span><span class="o">)</span> <span class="o">{</span>
<span class="c1">//and line comments are ignored too</span>
<span class="o">}</span>
</code></pre></div></div>
<ul>
<li>implicit and explicit elements are considered the same. For example:</li>
</ul>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">if</span> <span class="o">(</span><span class="n">something</span><span class="o">)</span>
<span class="n">list</span> <span class="o">=</span> <span class="o">(</span><span class="nc">List</span><span class="o"><</span><span class="nc">String</span><span class="o">>)</span> <span class="k">new</span> <span class="nc">ArrayList</span><span class="o"><>(</span><span class="no">FIELD_COUNT</span><span class="o">);</span>
<span class="c1">//matches with</span>
<span class="k">if</span> <span class="o">(</span><span class="n">something</span><span class="o">)</span> <span class="o">{</span>
<span class="nc">OuterType</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">list</span> <span class="o">=</span> <span class="o">(</span><span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">List</span><span class="o"><</span><span class="n">java</span><span class="o">.</span><span class="na">lang</span><span class="o">.</span><span class="na">String</span><span class="o">>)</span> <span class="k">new</span> <span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">ArrayList</span><span class="o"><</span><span class="n">java</span><span class="o">.</span><span class="na">lang</span><span class="o">.</span><span class="na">String</span><span class="o">>(</span><span class="nc">Constants</span><span class="o">.</span><span class="na">FIELD_COUNT</span><span class="o">);</span>
<span class="o">}</span>
</code></pre></div></div>
<ul>
<li>casts are skipped. For example:</li>
</ul>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">f</span><span class="o">(</span><span class="n">x</span><span class="o">);</span>
<span class="c1">//matches with</span>
<span class="o">(</span><span class="nc">Object</span><span class="o">)</span> <span class="n">f</span><span class="o">(</span><span class="n">x</span><span class="o">);</span>
</code></pre></div></div>
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