[Bug] Selections with unions fail if one of the sets is empty

[mroy-seedbox]

Is this a new bug in dbt-core?

• I believe this is a new bug in dbt-core
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

tl;dr: Unions should be able to handle empty sets. There is no programming language which crashes when doing the union of empty arrays/list/sets/etc.

When doing unions in an evolving project, models will come and go (and thus some selections/sets may be empty). However, dbt seems unable to handle this, and returns an error instead.

For example: dbt ls -s something,tag:one something,tag:two ...

If the last tag:one or tag:two model is removed from something, then the entire selection will fail, and as a result the entire job/pipeline will fail also.

Error message:

Compilation Error
  The selection criterion 'something,tag:one|two' does not match any enabled nodes

Expected Behavior

Empty sets are simply ignored.

Or maybe introduce a new parameter in the CLI, something like --ignore-empty-sets, or --ignore-empty-selection. It should be a fairly simple change: if the parameter is set, do not throw this error. It would be the most explicit option, while also preserving backward-compatibility.

Alternatives Considered

• Excluding anything which is neither tag:one or tag:two (i.e. dbt ls -s something --exclude tag:not_one_or_two), but there is no way to do this currently.
• Mixing CLI selection with YAML selectors (i.e. dbt ls -s something,selector:one_or_two), but that is not supported currently (edit: see issue [Feature] add selector: method to combine YAML selectors with command line selection #10992).

Steps To Reproduce

Do a union with an empty set. See above for more details.

Relevant log output

No response

Environment

- OS: Any
- Python: Any
- dbt: 1.8.8 (but happens in any version)

Which database adapter are you using with dbt?

Any.

Additional Context

No response

[mroy-seedbox]

#10992 would offer a clean solution to for this issue.

[mroy-seedbox]

Actually, there is already a solution for this!

We can specify NoNodesForSelectionCriteria in the warn_error_options flag/config (see documentation here).

Closing this issue! 🎉