diff options
| -rw-r--r-- | lib/attrsets.nix | 11 | ||||
| -rw-r--r-- | lib/tests.nix | 10 |
2 files changed, 21 insertions, 0 deletions
diff --git a/lib/attrsets.nix b/lib/attrsets.nix index 22ecc808679..84f6cb3658b 100644 --- a/lib/attrsets.nix +++ b/lib/attrsets.nix @@ -23,6 +23,17 @@ rec { then attrByPath (tail attrPath) default e.${attr} else default; + /* Return if an attribute from nested attribute set exists. + For instance ["x" "y"] applied to some set e returns true, if e.x.y exists. False + is returned otherwise. */ + hasAttrByPath = attrPath: e: + let attr = head attrPath; + in + if attrPath == [] then true + else if e ? ${attr} + then hasAttrByPath (tail attrPath) e.${attr} + else false; + /* Return nested attribute set in which an attribute is set. For instance ["x" "y"] applied with some value v returns `x.y = v;' */ diff --git a/lib/tests.nix b/lib/tests.nix index 1fb2cbf5b53..c3b8839fda9 100644 --- a/lib/tests.nix +++ b/lib/tests.nix @@ -120,4 +120,14 @@ runTests { expected = { success = false; value = false; }; }; + testHasAttrByPathTrue = { + expr = hasAttrByPath ["a" "b"] { a = { b = "yey"; }; }; + expected = true; + }; + + testHasAttrByPathFalse = { + expr = hasAttrByPath ["a" "b"] { a = { c = "yey"; }; }; + expected = false; + }; + } |