[Question] LOGBACK-1731 using variables in path names

[rPraml]

Hello, we are facing the same issue mentioned in https://jira.qos.ch/browse/LOGBACK-1731 and we hoped, it will be fixed in 1.4.12 (as it is listed in fix-versions)

It seems that there was a change in when we migrated from 1.2 to 1.4
Using scope="system" seems to work in spring.

It seems that there is some logical order problem
As far as I could debug the issue, logback builds a "Model" which represents the complete config (with all included files)
and then, the properties are evolved. So due this order problem, it is not possible to use parameters in include tags. (Note: I'm not very familiar with the architecture in logback, so this is just a guess, what I've ssen in debugger)

When you apply scope="system" - logback puts the value in the system-properties. As spring reloads the logback config at least once, the next run can access the value from the previous run.

Note: we do not really rely on this issue if our use cases could be solved in an other way

Our use cases

1. We want to include an optional properties file (which might not exist)

Preferred solution:

<property file="config/application-local.properties" optional="true"/>

This does not work, because there is no optional support for property and the produced error will prevent spring to run the application

Current solution:

<!-- We define a property, that evaluates to "true", if the file exists -->
<define name="APPLICATION_LOCAL_EXISTS" class="ch.qos.logback.core.property.FileExistsPropertyDefiner" scope="system">
	<path>config/application-local.properties</path>
</define>
<!-- if file exists, we include  application-local.properties-true.inc.xml. 
     If the property file does not exist, no XML is found. 
     This works, because 'include' supports 'optional=true' -->
<include resource="logback/application-local.properties-${APPLICATION_LOCAL_EXISTS}.inc.xml" optional="true"/>

<!-- content of application-local.properties-true.inc.xml -->
<included>
	<property file="config/application-local.properties"/>
</included>

Yes this is a workaround, and I'm sure it was not intended to use it this way, but it did work with 1.2

possible fix
Add 'optional' to 'property'

2. We want to include different appenders.

<property name="consoleAppender" value="${de.foconis.log.console.appender:-CONSOLE}" scope="system"/>
<root>
	<appender-ref ref="${consoleAppender}"/>
</root>

By default we want to use the CONSOLE appender, we have also other appenders like CONSOLE_ANSI, CONSOLE_JSON which formats the output to console in a different way.

If we put all appenders "ready for use" in the logback.xml we get warnings like Appender named [CONSOLE_ANSI] not referenced. Skipping further processing. - so we split them up into a CONSOLE.appender.inc.xml, CONSOLE_ANSI.appender.inc.xml, CONSOLE_JSON.inc.xml and include the dedicated file with

<include optional="true" resource="logback/${consoleAppender}.appender.inc.xml"/>

possible fix
Add 'optionalUse' to 'appender'. If this is set, no warnings are printed, if appender is not in use.

[rPraml]

Use case 1 would be solved by #511