Add a warning for logfiles if the log file does not exist or is not found

[darshie]

I've noticed that there is no warning in the logs if i try to read a log file from disk using logfiles.

f.addStep(ShellCommand(
                        command=["make", "test"],
                        logfiles={"disk_log": "/slavebot/testbuild/test.log"}))

In this case if the file cannot be found, an empty file called test.log will be created and added to the waterfall page.

Would be useful to have a warning in the logs so is possible to know if the file exist or not, and troubleshoot why a log file is not displayed in the waterfall page, instead than just showing an empty file.

Thanks

[callek]

Should this show a warning in waterfall of "log {logfilename} not found [details]" or actually be represented as if it is the logfiles contents?

I think the *way* we expose this data matters, and would be relatively representative of how difficult this is to do.

[verm]

Expressed in the waterfall some how I would think. A 0-byte log file lets the end-user know nothing was logged anything above that may lead to the assumption the correct data was logged rather than a warning/error from buildbot.

[dustin]

This should probably just cause the buildstep to fail, with a suitable error message.