I'd like to propose adding two new operators, or rather extending the existing USE dependency operators with an 'arrow' syntax to allow dependee flag name to be different. Killer rationale: we have 2-style and 4-style USE dependencies. We inevitably need to have 8-style USE dependencies, and then we're good till EAPI 16. New syntax ========== The new USE dependency syntax I'd like to see is (square brackets indicate optional parts): [!]a?>[-]b meaning 'if a is enabled (disabled) on this package, require b to be enabled (disabled) on the other package', and: [!]a=>[-]b meaning the above + 'and vice versa'. Expanded forms ============== a?>b <=> a? ( ...[b] ) !a?>b <=> !a? ( ...[b] ) a?>-b <=> a? ( ...[-b] ) !a?->-b <=> !a? ( ...[-b] ) a=>b <=> a? ( ...[b] ) !a? ( ...[-b] ) !a=>b <=> !a? ( ...[b] ) a? ( ...[-b] ) a=>-b <=> a? ( ...[-b] ) !a? ( ...[b] ) !a=>-b <=> !a? ( ...[-b] ) a? ( ...[b] ) Naturally, the => forms are equivalent in pairs. Equivalent same-flag forms ========================== a? <=> a?>a !a? <=> !a?>-a a= <=> a=>a !a= <=> !a=>-a While they're obviously redundant, I believe that at least '!a?' is less readable (counter-intuitive) than the expanded form. Use cases ========= I can think of two primary USE cases for it. Firstly, python-single-r1 ebuilds with new API could be simplified. Currently, they do: pst1? ( ...[pt1] ) pst2? ( ...[pt2] ) ... With the new syntax, they could generate a PYTHON_MULTI_USEDEP having: pst1?>pt1,pst2?>pt2,... Secondly, static-enabled ebuilds. They currently do, usually via a gross hack: dev-libs/foo static? ( dev-libs/foo[static-libs(+)] ) The new syntax would allow: dev-libs/foo[static?>static-libs(+)]
