Sandbox::https://github.com/github/codeql/blob/main/java/ql/src/Compatibility/JDK9/UnderscoreIdentifier.ql

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/**

* @name Underscore used as identifier

* @description Use of a single underscore character as an identifier

* results in a compiler error with Java source level 9 or later.

* @kind problem

* @problem.severity recommendation

* @precision high

* @id java/underscore-identifier

* @tags quality

* maintainability

* readability

import java

class IdentifierElement extends Element {

IdentifierElement() {

this instanceof CompilationUnit or

this.(RefType).isSourceDeclaration() or

this.(Callable).isSourceDeclaration() or

this instanceof Variable

}

from IdentifierElement e, string msg

where

e.getCompilationUnit().isJavaSourceFile() and

not e.(Constructor).isDefaultConstructor() and

(

e.getName() = "_" and

msg = "."

e.(CompilationUnit).getPackage().getName().splitAt(".") = "_" and

msg = " in package name '" + e.(CompilationUnit).getPackage().getName() + "'."

)

select e, "Use of underscore as a one-character identifier" + msg