Add a system property to configure the daemon log level

[wolfs]

Related to #2688

Currently, the daemon always logs with DEBUG log level in the daemon log. This was fine up to now (mostly), since not much happened between builds.

When file watching is enabled, a lot happens between builds - file changes are collected. In order to prevent the daemon log to overflow, it should be possible to set the log level differently - e.g. to INFO.

This PR introduces a system property org.gradle.daemon.loglevel which the daemon tries to pick up from the current build context and then changes the logging level after the build accordingly.

[lptr]

LGTM. Can't we simulate org.gradle.daemon.disable-output by setting the log level to OFF now?

[wolfs]

No, org.gradle.daemon.disable-output only disables the output to the console while the build is running, not to the daemon log.

[lptr]

In that case I think we should re-initialize the log level before we check that switch.

[wolfs]

If we re-initialize logging before checking org.gradle.daemon.disable-output, then setting the logging doesn't work anymore, since stopping the logging router will reset the logging to the previous state, which is whatever the daemon had at the beginning.

[wolfs]

Switching to info doesn't seem feasible, since then we lose the timestamps in the daemon logs, which seem to be important for users. It seems hard to produce timestamps with info logging in the daemon logs, since the logs are emitted by StyledTextOutputBackedRenderer for all consumers, and those either contain the timestamps (debug log), or they don't. All the meta-data is lost for the downstream consumers of the log messages.

Closing this PR.