Circular import

A stylesheet that imports or includes itself, directly or through a chain of modules that pulls it back, is a static error, and the processor refuses to compile it. Move the shared code into a third module both import.

Incorrect (a.xsl and b.xsl import each other):

<!-- a.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="b.xsl"/>
</xsl:stylesheet>

<!-- b.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="a.xsl"/>
</xsl:stylesheet>

Correct:

<!-- a.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="common.xsl"/>
</xsl:stylesheet>

<!-- b.xsl -->
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:import href="common.xsl"/>
</xsl:stylesheet>

A cycle is reported only when every module in it is among the linted files.