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author | Silvan Mosberger <silvan.mosberger@tweag.io> | 2023-06-16 00:19:33 +0200 |
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committer | Silvan Mosberger <silvan.mosberger@tweag.io> | 2023-07-10 21:25:43 +0200 |
commit | 6626d8cc4de80f063da7ab871ecdc66f40f28e0b (patch) | |
tree | 1c4f1874c16d2a62f3736542a896023718ed4862 /lib/path/default.nix | |
parent | 7a49b67eb2dd419d4a6d4ae4e968d64fd051f140 (diff) |
lib.path.removePrefix: init
Diffstat (limited to 'lib/path/default.nix')
-rw-r--r-- | lib/path/default.nix | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/lib/path/default.nix b/lib/path/default.nix index 936e9b0302534..3a871bc05283c 100644 --- a/lib/path/default.nix +++ b/lib/path/default.nix @@ -20,6 +20,7 @@ let concatMap foldl' take + drop ; inherit (lib.strings) @@ -217,6 +218,58 @@ in /* No rec! Add dependencies on this file at the top. */ { second argument: "${toString path2}" with root "${toString path2Deconstructed.root}"''; take (length path1Deconstructed.components) path2Deconstructed.components == path1Deconstructed.components; + /* + Remove the first path as a component-wise prefix from the second path. + The result is a normalised subpath string, see `lib.path.subpath.normalise`. + + Laws: + + - Inverts `append` for normalised subpaths: + + removePrefix p (append p s) == subpath.normalise s + + Type: + removePrefix :: Path -> Path -> String + + Example: + removePrefix /foo /foo/bar/baz + => "./bar/baz" + removePrefix /foo /foo + => "./." + removePrefix /foo/bar /foo + => <error> + removePrefix /. /foo + => "./foo" + */ + removePrefix = + path1: + assert assertMsg + (isPath path1) + "lib.path.removePrefix: First argument is of type ${typeOf path1}, but a path was expected."; + let + path1Deconstructed = deconstructPath path1; + path1Length = length path1Deconstructed.components; + in + path2: + assert assertMsg + (isPath path2) + "lib.path.removePrefix: Second argument is of type ${typeOf path2}, but a path was expected."; + let + path2Deconstructed = deconstructPath path2; + success = take path1Length path2Deconstructed.components == path1Deconstructed.components; + components = + if success then + drop path1Length path2Deconstructed.components + else + throw '' + lib.path.removePrefix: The first path argument "${toString path1}" is not a component-wise prefix of the second path argument "${toString path2}".''; + in + assert assertMsg + (path1Deconstructed.root == path2Deconstructed.root) '' + lib.path.removePrefix: Filesystem roots must be the same for both paths, but paths with different roots were given: + first argument: "${toString path1}" with root "${toString path1Deconstructed.root}" + second argument: "${toString path2}" with root "${toString path2Deconstructed.root}"''; + joinRelPath components; /* Whether a value is a valid subpath string. |