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Diffstat (limited to 'lib/asserts.nix')
-rw-r--r-- | lib/asserts.nix | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/lib/asserts.nix b/lib/asserts.nix new file mode 100644 index 00000000000..9ae357cbc93 --- /dev/null +++ b/lib/asserts.nix @@ -0,0 +1,42 @@ +{ lib }: + +rec { + + /* Throw if pred is false, else return pred. + Intended to be used to augment asserts with helpful error messages. + + Example: + assertMsg false "nope" + stderr> error: nope + + assert assertMsg ("foo" == "bar") "foo is not bar, silly"; "" + stderr> error: foo is not bar, silly + + Type: + assertMsg :: Bool -> String -> Bool + */ + # TODO(Profpatsch): add tests that check stderr + assertMsg = pred: msg: + pred || builtins.throw msg; + + /* 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" ] + stderr> error: sslLibrary must be one of [ + stderr> "openssl" + stderr> "bearssl" + stderr> ], 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}"; + +} |