user/src/com/google/gwt/logging/LogImpl.gwt.xml

<module type="fileset">
  <inherits name="com.google.gwt.core.Core"/>

  <source path="impl" />

  <!-- Set up and handle the gwt.logging property
   Setting this value to FALSE will compile out all logging.  Setting it to SEVERE
   or WARNING means that the logging framework will not compile out, but the basic
   logging calls like logger.info() and logger.fine() will compile out if it is below
   the level that is set.  Note that something like logger.log(Level.INFO, "foo", e)
   *will not* compile out at this point.  If you have something that is important to 
   have compiled out, you should put it behind a 
   LogConfiguration.isLoggingEnabled(Level.INFO) guard.
   -->
  <define-property name="gwt.logging.enabled" values="TRUE, FALSE, SEVERE, WARNING" />
  <replace-with class="com.google.gwt.logging.impl.LevelImplRegular">
    <when-type-is class="com.google.gwt.logging.impl.LevelImplNull"/>
    <any>
      <when-property-is name="gwt.logging.enabled" value="TRUE" />
      <when-property-is name="gwt.logging.enabled" value="SEVERE" />
      <when-property-is name="gwt.logging.enabled" value="WARNING" />
    </any>
  </replace-with>

  <replace-with class="com.google.gwt.logging.impl.LoggerImplRegular">
    <when-type-is class="com.google.gwt.logging.impl.LoggerImplNull"/>
    <when-property-is name="gwt.logging.enabled" value="TRUE" />
  </replace-with>
  <replace-with class="com.google.gwt.logging.impl.LoggerImplSevere">
    <when-type-is class="com.google.gwt.logging.impl.LoggerImplNull"/>
    <when-property-is name="gwt.logging.enabled" value="SEVERE" />
  </replace-with>
  <replace-with class="com.google.gwt.logging.impl.LoggerImplWarning">
    <when-type-is class="com.google.gwt.logging.impl.LoggerImplNull"/>
    <when-property-is name="gwt.logging.enabled" value="WARNING" />
  </replace-with>
  
  <set-property name="gwt.logging.enabled" value="FALSE"/> 

  <replace-with class="com.google.gwt.logging.impl.LoggerConfiguratorNull">
    <when-type-is class="com.google.gwt.logging.impl.LoggerConfigurator"/>
  </replace-with>

  <!-- Enable simple console logging by default for superdevmode -->
  <replace-with class="com.google.gwt.logging.impl.LoggerConfiguratorConsole">
    <when-type-is class="com.google.gwt.logging.impl.LoggerConfigurator"/>
    <when-property-is name="superdevmode" value="on"/>
  </replace-with>
  <set-property name="gwt.logging.enabled" value="TRUE">
    <when-property-is name="superdevmode" value="on"/>
  </set-property>
</module>