v3.1.0 does not allow empty file names anymore for RollingFileAppender

[mordio]

This works until v3.0.4:

<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
  <lockingModel type="log4net.Appender.FileAppender+MinimalLock"/>
  <file value="logs\"/>
  <encoding value="utf-8" />
  <datePattern value="yyyy-MM-dd'.log'"/>
  <staticLogFileName value="false"/>
  <appendToFile value="true"/>
  <rollingStyle value="Composite"/>
  <maxSizeRollBackups value="10"/>
  <maximumFileSize value="5MB"/>
  <layout type="log4net.Layout.PatternLayout">
    <conversionPattern value="%date [%property{id}] %-5level %logger - %message%newline"/>
  </layout>
</appender>

It creates log files in the subdirectory logs with names consisting of the date + .log like logs\2025-06-25.log.

With v3.1.0 an System.ArgumentException: The path is not of a legal form. is thrown:

log4net:ERROR Could not create Appender [RollingFileAppender] of type [log4net.Appender.RollingFileAppender]. Reported error follows.
System.ArgumentException: The path is not of a legal form.
   at System.IO.Path.NormalizePath(String path, Boolean fullCheck, Int32 maxPathLength, Boolean expandShortPaths)
   at System.IO.Path.InternalGetDirectoryName(String path)
   at log4net.Appender.RollingFileAppender.InitializeFromOneFile(String baseFile, String curFileName)
   at log4net.Appender.RollingFileAppender.InitializeRollBackups(String baseFile, IList`1 arrayFiles)
   at log4net.Appender.RollingFileAppender.DetermineCurSizeRollBackups()
   at log4net.Appender.RollingFileAppender.ExistingInit()
   at log4net.Appender.RollingFileAppender.ActivateOptions()
   at log4net.Repository.Hierarchy.XmlHierarchyConfigurator.ParseAppender(XmlElement appenderElement)
log4net:ERROR Appender named [RollingFileAppender] not found.

Workaround is to set <file> to something like <file value="logs\log_"/> and it creates logs\log_2025-06-25.log. Is there any way to produce file names like before?

Thanks for the good work!

[FreeAndNil]

@gdziadkiewicz this seems related to #257 - can you take a look?

[gdziadkiewicz]

Yes, will add it to tests and fix

[gdziadkiewicz]

It is the same issue as in #244, which was fixed in #251. I'm still adding the test to prevent regression in the future.