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Showing content from https://docs.pmd-code.org/pmd-doc-7.3.0/pmd_userdocs_extending_writing_xpath_rules.html below:

Writing XPath rules | PMD Source Code Analyzer

This page describes XPath rule support in more details

Table of Contents

This page describes some points of XPath rule support in more details. See also the tutorial about how to write a first (XPath) rule.

XPath version

PMD uses XPath 3.1 for its XPath rules since PMD 7. Before then, the default version was XPath 1.0, with opt-in support for XPath 2.0.

See the Saxonica documentation for an introduction to new features in XPath 3.1.

The property version of XPathRule is deprecated and has been removed with PMD 7.

DOM representation of ASTs

XPath rules view the AST as an XML-like DOM, which is what the XPath language is defined on. Concretely, this means:

Every AST node is viewed as an XML element
- The element has for local name the value of getXPathNodeName for the given node
Some Java getters are exposed as XML attributes on those elements
- This means, that documentation for attributes can be found in our Javadocs. For example, the attribute @SimpleName of the Java node EnumDeclaration is backed by the Java getter getSimpleName.

Value conversion

To represent attributes, we must map Java values to XPath Data Model (XDM) values. In the following table we refer to the type conversion function as conv, a function from Java types to XDM types.

Java type T XSD type conv(T) int xs:integer long xs:integer double xs:decimal float xs:decimal boolean xs:boolean String xs:string Character xs:string Enum<E> xs:string (uses Object::toString) Collection<E> conv(E)* (a sequence type)

The same conv function is used to translate rule property values to XDM values.

Additionaly, PMDâs own net.sourceforge.pmd.lang.document.Chars is also translated to a xs:string

Rule properties

See Defining rule properties

PMD extension functions

PMD provides some language-specific XPath functions to access semantic information from the AST.

The namespace of custom PMD functions must be explicitly mentioned.

All languages

Functions available to all languages are in the namespace pmd.

Function name Description (click for details) fileName Returns the simple name of the current file

Returns the current simple file name, without path but including the extension. This can be used to write rules that check file naming conventions.

Since

PMD 6.38.0

Remarks

The requires the context node to be an element

Examples

//b[pmd:fileName() = 'Foo.xml']: Matches any  tags in files called Foo.xml.

startLine Returns the start line of the given node

Returns the line where the node starts in the source file. Line numbers are 1-based.

Since

PMD 6.44.0

Remarks

The function is not context-dependent, but takes a node as its first parameter.

Parameters

element as xs:element: Any element node

Examples

//b[pmd:startLine(.) > 5]: Matches any  node which starts after the fifth line.

endLine Returns the end line of the given node

Returns the line where the node ends in the source file. Line numbers are 1-based.

Since

PMD 6.44.0

Remarks

The function is not context-dependent, but takes a node as its first parameter.

Parameters

element as xs:element: Any element node

Examples

//b[pmd:endLine(.) == pmd:startLine(.)]: Matches any  node which doesn't span more than one line.

startColumn Returns the start column of the given node (inclusive) pmd:startColumn(xs:element) as xs:int

Returns the column number where the node starts in the source file. Column numbers are 1-based. The start column is inclusive.

Since

PMD 6.44.0

Remarks

The function is not context-dependent, but takes a node as its first parameter.

Parameters

element as xs:element: Any element node

Examples

//b[pmd:startColumn(.) = 1]: Matches any  node which starts on the first column of a line

endColumn Returns the end column of the given node (exclusive) pmd:endColumn(xs:element) as xs:int

Returns the column number where the node ends in the source file. Column numbers are 1-based. The end column is exclusive.

Since

PMD 6.44.0

Remarks

The function is not context-dependent, but takes a node as its first parameter.

Parameters

element as xs:element: Any element node

Examples

//b[pmd:startLine(.) = pmd:endLine(.) and pmd:endColumn(.) - pmd:startColumn(.) = 1]: Matches any  node which spans exactly one character

Java

Java functions are in the namespace pmd-java.

Function name Description (click for details) nodeIs Tests the runtime type of the node instance

Returns true if the runtime type of the AST node is a subtype of the given class. Contrary to typeIs, this tests the type of the AST node. For example, the AST node for a literal (e.g. 5d) has type ASTNumericLiteral, and this function will ignore the static type of the expression (double)

Remarks

Parameters

nodeClassName as xs:string: Simple name of a class or interface in package net.sourceforge.pmd.lang.java.ast, without the 'AST' prefix

Examples

//*[pmd-java:nodeIs("Expression")]: Matches all nodes that implement ASTExpression
//*[pmd-java:nodeIs("TypeDeclaration")]: Matches all nodes that implement ASTTypeDeclaration
//*[pmd-java:nodeIs("Foo")]: Runtime error, there's no class ASTFoo in the package

typeIs Tests a node's static type

Returns true if the context node's static Java type is a subtype of the given type. This tests for the resolved type of the Java construct, not the type of the AST node. For example, the AST node for a literal (e.g. 5d) has type ASTNumericLiteral, however this function will compare the type of the literal (eg here, double) against the argument.

Remarks

The context node must be a TypeNode

Parameters

javaQualifiedName as xs:string: The qualified name of a Java class, possibly with pairs of brackets to indicate an array type. Can also be a primitive type name.

Examples

//FormalParameter[pmd-java:typeIs("java.lang.String[]")]: Matches formal parameters of type String[] (including vararg parameters)
//VariableId[pmd-java:typeIs("java.lang.List")]: Matches variable declarators of type List or any of its subtypes (including e.g. ArrayList)

typeIsExactly Tests a node's static type, ignoring subtypes

Returns true if the context node's static type is exactly the given type. In particular, returns false if the context node's type is a subtype of the given type.

Remarks

The context node must be a TypeNode

Parameters

javaQualifiedName as xs:string: The qualified name of a Java class, possibly with pairs of brackets to indicate an array type. Can also be a primitive type name.

Examples

//VariableId[pmd-java:typeIsExactly("java.lang.List")]: Matches variable declarators of type List (but not e.g. ArrayList)

metric Computes and returns the value of a metric

Returns the value of the metric as evaluated on the context node. If the metric cannot be computed on that node, returns an empty sequence (which is falsy).

Remarks

Parameters

metricKey as xs:string: The name of a metric in JavaMetrics (or an alias thereof).

Examples

//ClassDeclaration[metric('NCSS') > 200]
//MethodDeclaration[metric('CYCLO') > 10 and metric('NCSS') > 20]
//TypeParameter[metric('idontexist') > 50]: Error: no such metric

hasAnnotation Tests whether an annotation is present on the node

Returns true if the node has an annotation with the given qualified name

Remarks

The context node must be an Annotatable, otherwise this returns false

Parameters

annotationClassName as xs:string: Canonical name of an annotation type

Examples

//MethodDeclaration[pmd-java:hasAnnotation("java.lang.Override")]: Matches all method declarations that are annotated with @Override

modifiers Produce the effective modifiers of a node

Returns a sequence of the effective modifiers of a node as strings. This is documented on getEffectiveModifiers.

Remarks

The context node must be an ModifierOwner, otherwise this returns an empty sequence

Examples

//MethodDeclaration[pmd-java:modifiers() = "native"]: Matches native method declarations
//MethodDeclaration[pmd-java:modifiers() = ("native", "static")]: Matches method declarations that have a 'native' OR a 'static' modifier. This may be counter-intuitive.
//MethodDeclaration[pmd-java:modifiers() = "public"]: Matches method declarations that have a 'public' modifier, explicit or implicit. For example, this would match methods in interfaces, which implicitly have the modifier. Use the explicitModifiers function if you don't want the implicit part. Also note that @Visibility = 'public' is a better use of the API, in this particular instance.

explicitModifiers Produce the explicit modifiers of a node

Returns a sequence of the explicit modifiers of a node as strings. This is documented on getExplicitModifiers.

Remarks

The context node must be an ModifierOwner, otherwise this returns an empty sequence

Examples

//MethodDeclaration[pmd-java:explicitModifiers() = "public"]: Matches method declarations that have an explicit 'public' modifier.

matchesSig Matches the signature called by a method or constructor call

Uses an TypeTestUtil.InvocationMatcher to test the method signature called by the context node. The format of the parameter is described on that class.

Remarks

The context node must be an InvocationNode, otherwise this returns false

Parameters

sig as xs:string: A signature, in the format described on TypeTestUtil.InvocationMatcher

Examples

//MethodCall[pmd-java:matchesSig("_#equals(java.lang.Object)")]: Matches calls to the method equals on any receiver type
//MethodCall[pmd-java:matchesSig("java.lang.Enum#equals(java.lang.Object)")]: Matches calls to the method equals on receiver that is a subtype of Enum
//MethodCall[pmd-java:matchesSig("java.lang.String#toString()")]: Matches calls to the method toString on String receivers
//MethodCall[pmd-java:matchesSig("_#_(int,int)")]: Matches calls to any method with 2 int parameters (!= argument)
//ConstructorCall[pmd-java:matchesSig("java.util.ArrayList#new(int)")]: Matches constructors calls of ArrayList with a single int parameter

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