Obviously they are very useful. I still don't think they should exist in this usage of yaml.
Once you allow setting and reading of variables in a configuration file, you lose the safety that makes the format useful. You might as well be using a bash script at that point.
You already can set and read variables. The `matrix` section is often used to test against multiple versions of software. Environment variables can be referenced. And the project configuration supports both secrets and variables configured at the project level.
Once you allow setting and reading of variables in a configuration file, you lose the safety that makes the format useful. You might as well be using a bash script at that point.