travis-ci/travis-core — pull request #289 by drogus (2013-11-13 11:01:51+00:00)
Title: Config should raise an error if both file and env configs are available

We use file configs for some apps and ENV config for the others. When
both configs are available (for example because someone accidentally set
an ENV config where file config is already set), Travis.config will
silently prefer ENV over file config.

I have tested this on staging and it raises on such situation properly.