hasStorePathPrefix

lib.path.hasStorePathPrefix

Docs pulled from | This Revision | about 1 hour ago

Whether a path has a store path as a prefix.

As with all functions of this lib.path library, it does not work on paths in strings, which is how you'd typically get store paths.

Instead, this function only handles path values themselves, which occur when Nix files in the store use relative path expressions.

Inputs

path: 1. Function argument

Type

hasStorePathPrefix :: Path -> Bool

Examples

`hasStorePathPrefix` usage example

# Subpaths of derivation outputs have a store path as a prefix
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo/bar/baz
=> true

# The store directory itself is not a store path
hasStorePathPrefix /nix/store
=> false

# Derivation outputs are store paths themselves
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo
=> true

# Paths outside the Nix store don't have a store path prefix
hasStorePathPrefix /home/user
=> false

# Not all paths under the Nix store are store paths
hasStorePathPrefix /nix/store/.links/10gg8k3rmbw8p7gszarbk7qyd9jwxhcfq9i6s5i0qikx8alkk4hq
=> false

# Store derivations are also store paths themselves
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo.drv
=> true

Noogle detected

Implementation

The following is the current implementation of this function.

hasStorePathPrefix =
    path:
    let
      deconstructed = deconstructPath path;
    in
    assert assertMsg (isPath path)
      "lib.path.hasStorePathPrefix: Argument is of type ${typeOf path}, but a path was expected";
    assert assertMsg
      # This function likely breaks or needs adjustment if used with other filesystem roots, if they ever get implemented.
      # Let's try to error nicely in such a case, though it's unclear how an implementation would work even and whether this could be detected.
      # See also https://github.com/NixOS/nix/pull/6530#discussion_r1422843117
      (deconstructed.root == /. && toString deconstructed.root == "/")
      "lib.path.hasStorePathPrefix: Argument has a filesystem root (${toString deconstructed.root}) that's not /, which is currently not supported.";
    componentsHaveStorePathPrefix deconstructed.components;