{ lib }: rec { /* Print a trace message if pred is false. Intended to be used to augment asserts with helpful error messages. Example: assertMsg false "nope" => false stderr> trace: nope assert (assertMsg ("foo" == "bar") "foo is not bar, silly"); "" stderr> trace: foo is not bar, silly stderr> assert failed at … Type: assertMsg :: Bool -> String -> Bool */ # TODO(Profpatsch): add tests that check stderr assertMsg = pred: msg: if pred then true else builtins.trace msg false; /* Specialized `assertMsg` for checking if val is one of the elements of a list. Useful for checking enums. Example: let sslLibrary = "libressl" in assertOneOf "sslLibrary" sslLibrary [ "openssl" "bearssl" ] => false stderr> trace: sslLibrary must be one of "openssl", "bearssl", but is: "libressl" Type: assertOneOf :: String -> ComparableVal -> List ComparableVal -> Bool */ assertOneOf = name: val: xs: assertMsg (lib.elem val xs) "${name} must be one of ${ lib.generators.toPretty {} xs}, but is: ${ lib.generators.toPretty {} val}"; }