These are the docs for an older version of OPA. Latest stable release is v0.46.1
Compiler Strict Mode Edit

The Rego compiler supports strict mode, where additional constraints and safety checks are enforced during compilation. Compiler rules that will be enforced by future versions of OPA, but will be a breaking change once introduced, are incubated in strict mode. This creates an opportunity for users to verify that their policies are compatible with the next version of OPA before upgrading.

Compiler Strict mode is supported by the check command, and can be enabled through the -S flag.

-S, --strict enable compiler strict mode

Strict Mode Constraints and Checks

Name Description Enforced by default in OPA version
Duplicate imports Duplicate imports, where one import shadows another, are prohibited. 1.0
Unused local assignments Unused assignments local to a rule, function or comprehension are prohibited 1.0
Unused imports Unused imports are prohibited. 1.0
input and data reserved keywords input and data are reserved keywords, and may not be used as names for rules and variable assignment. 1.0
any() and all() removed The any() and all() built-in functions have been deprecated, and will be removed in OPA 1.0. Use of these functions is prohibited. 1.0