diff options
| -rw-r--r-- | lib/default.nix | 3 | ||||
| -rw-r--r-- | lib/trivial.nix | 20 |
2 files changed, 22 insertions, 1 deletions
diff --git a/lib/default.nix b/lib/default.nix index dd6fcec75e21..fd3be3c6f4bc 100644 --- a/lib/default.nix +++ b/lib/default.nix @@ -59,7 +59,8 @@ let inherit (trivial) id const concat or and bitAnd bitOr bitXor bitNot boolToString mergeAttrs flip mapNullable inNixShell min max importJSON warn info nixpkgsVersion version mod compare - splitByAndCompare functionArgs setFunctionArgs isFunction; + splitByAndCompare functionArgs setFunctionArgs isFunction + assertMsg; inherit (fixedPoints) fix fix' extends composeExtensions makeExtensible makeExtensibleWithCustomName; diff --git a/lib/trivial.nix b/lib/trivial.nix index e702b8cdcc9f..bba284548d98 100644 --- a/lib/trivial.nix +++ b/lib/trivial.nix @@ -188,6 +188,26 @@ rec { warn = msg: builtins.trace "WARNING: ${msg}"; info = msg: builtins.trace "INFO: ${msg}"; + /* 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 + */ + assertMsg = pred: msg: + if pred + then true + else builtins.trace msg false; + ## Function annotations |