#18387 Steer users away from using multiple interpreter constraints Issue created by huonw Is your feature request related to a problem? Please describe. Pants theoretically supports multiple Python interpreter constraints, e.g.

interpreter_constraints = ["CPython==3.8.*", "CPython==3.9.*"]

. However, it seems like this is (strongly) not recommended, and leads to strange behaviour, and a lot of questions in Slack: 1. https://pantsbuild.slack.com/archives/C046T6T9U/p1677698844617669 2. https://pantsbuild.slack.com/archives/C046T6T9U/p1668095636694669?thread_ts=1668089867.223149&cid=C046T6T9U (particularly subtle issues around appending to the ICs list implicitly!) 3. https://pantsbuild.slack.com/archives/C046T6T9U/p1670512567148199 Background from @enough-analyst-54434 in that last thread:

the affordance for OR was added purely for Twitter internal needs back in the Pants v1 days. They never actually needed the feature and could've spelled what they needed with a range + ,!=X,!=Y,etc. Unfortunately that is still lying around and is really legacy. Although this is certainly a bug, be warned - best to stay away from use of the OR facility. It is non-standard in the Python world and non-standard will always get you in the end.

For instance: •

interpreter_constraints = ["CPython==3.8.*", "CPython==3.9.*"]

should be something like

interpreter_constraints = ["CPython==3.8.*,==3.9.*"]

•

interpreter_constraints = ["CPython==2.7.*", "CPython>=3.7.*"]

should be something like

interpreter_constraints = [">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,!=3.6.*"]

Describe the solution you'd like It seems like the situation could be improved by deprecating setting

interpreter_constraints

to a list with more than one element (and/or not deprecate it, but require opt-in like

allow_non_pypa_multiple_interpreter_constaints = true

or similar), with a warning that suggests how using a single constraint (with exclusions, if required) is better. Preferably, Pants could move towards having

interpreter_constraints

be just a plain string

interpreter_contraints = "CPython==...,==..."

to set the appropriate single IC directly (without the implicit appending that caused the confusion in thread 2 above). Describe alternatives you've considered 🤷‍♂️ Additional context N/A pantsbuild/pants