Buildbot WithProperties

Today, I copied an existing command from a Buildbot configuration and then modified it to print a date into a file.:

...
if "cargo" in component:
    cargo_date_cmd = "echo `date +'%Y-%m-%d'` > " + final_dist_dir + "/cargo-build-date.txt"
    f.addStep(MasterShellCommand(name="Write date to cargo-build-date.txt",
                             command=["sh", "-c", WithProperties(cargo_date_cmd)] ))
...

It broke:

Failure: twisted.internet.defer.FirstError: FirstError[#8, [Failure instance: Traceback (failure with no frames): : FirstError[#2, [Failure instance: Traceback: : unsupported format character 'Y' (0x59) at index 14

Why? WithProperties.

It turns out that WithProperties should only be used when you need to interpolate strings into an argument, using either %s, %d, or %(propertyname)s syntax in the string.

The lesson here is Buildbot will happily accept WithProperties("echo 'this command uses no interpolation'") in a command argument, and then blow up at you if you ever change the command to have a % in it.

http://edunham.net/2016/02/19/buildbot_withproperties.html