Policy: REQUIRED_USE

Concern: What hard USE constraints does an ebuild impose on itself?

PMS / Portage: REQUIRED_USE is a propositional constraint over IUSE (||, ^^, ??, flag? ( … ), …). Unsatisfied constraints block the build; emerge often suggests USE changes (autounmask).

Literals:

• required(Use) / required(minus(Use))
• blocking(Use) / blocking(minus(Use))
• Choice-group *:validate for REQUIRED_USE cardinality
• Assumptions: assumed(conflict(required,…)), required_use_violation

Owns: Rules/Resolving/use.pl, resolving.pl required/blocking clauses.

Invariants:

• REQUIRED_USE is evaluated against the effective USE for that ebuild (IUSE defaults + config + build_with_use).
• Violations that cannot be repaired by progressive relaxation are negative domain assumptions.
• Actionable USE flips appear as suggestion(use_change, …) when the plan proposes a config change.
• REQUIRED_USE is stricter than soft USE defaults from parents.

Examples: test32, test40, test49, test51, test63.
See also: USE, Assumptions.