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Diffstat (limited to 'nix/utils/default.nix')
| -rw-r--r-- | nix/utils/default.nix | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/nix/utils/default.nix b/nix/utils/default.nix new file mode 100644 index 000000000000..f65d4712a03d --- /dev/null +++ b/nix/utils/default.nix @@ -0,0 +1,180 @@ +{ depot, lib, ... }: + +let + /* Get the basename of a store path without + the leading hash. + + Type: (path | drv | string) -> string + + Example: + storePathName ./foo.c + => "foo.c" + + storePathName (writeText "foo.c" "int main() { return 0; }") + => "foo.c" + + storePathName "${hello}/bin/hello" + => "hello" + */ + storePathName = p: + if lib.isDerivation p + then p.name + else if builtins.isPath p + then builtins.baseNameOf p + else if builtins.isString p + then + let + # strip leading storeDir and trailing slashes + noStoreDir = lib.removeSuffix "/" + (lib.removePrefix "${builtins.storeDir}/" p); + # a basename of a child of a store path isn't really + # referring to a store path, so removing the string + # context is safe (e. g. "hello" for "${hello}/bin/hello"). + basename = builtins.unsafeDiscardStringContext + (builtins.baseNameOf p); + in + # If p is a direct child of storeDir, we need to remove + # the leading hash as well to make sure that: + # `storePathName drv == storePathName (toString drv)`. + if noStoreDir == basename + then builtins.substring 33 (-1) basename + else basename + else builtins.throw "Don't know how to get (base)name of " + + lib.generators.toPretty {} p; + + /* Query the type of a path exposing the same information as would be by + `builtins.readDir`, but for a single, specific target path. + + The information is returned as a tagged value, i. e. an attribute set with + exactly one attribute where the type of the path is encoded in the name + of the single attribute. The allowed tags and values are as follows: + + * `regular`: is a regular file, always `true` if returned + * `directory`: is a directory, always `true` if returned + * `missing`: path does not exist, always `true` if returned + * `symlink`: path is a symlink, value is a string describing the type + of its realpath which may be either: + + * `"directory"`: realpath of the symlink is a directory + * `"regular-or-missing`": realpath of the symlink is either a regular + file or does not exist. Due to limitations of the Nix expression + language, we can't tell which. + + Type: path(-like) -> tag + + `tag` refers to the attribute set format of `//nix/tag`. + + Example: + pathType ./foo.c + => { regular = true; } + + pathType /home/lukas + => { directory = true; } + + pathType ./result + => { symlink = "directory"; } + + pathType ./link-to-file + => { symlink = "regular-or-missing"; } + + pathType /does/not/exist + => { missing = true; } + + # Check if a path exists + !(pathType /file ? missing) + + # Check if a path is a directory or a symlink to a directory + # A handy shorthand for this is provided as `realPathIsDirectory`. + pathType /path ? directory || (pathType /path).symlink or null == "directory" + + # Match on the result using //nix/tag + nix.tag.match (nix.utils.pathType ./result) { + symlink = v: "symlink to ${v}"; + directory = _: "directory"; + regular = _: "regular"; + missing = _: "path does not exist"; + } + => "symlink to directory" + + # Query path type + nix.tag.tagName (pathType /path) + */ + pathType = path: + let + # baseNameOf is very annoyed if we proceed with string context. + # We need to call toString to prevent unsafeDiscardStringContext + # from importing a path into store which messes with base- and + # dirname of course. + path'= builtins.unsafeDiscardStringContext (toString path); + # To read the containing directory we absolutely need + # to keep the string context, otherwise a derivation + # would not be realized before our check (at eval time) + containingDir = builtins.readDir (builtins.dirOf path); + # Construct tag to use for the value + thisPathType = containingDir.${builtins.baseNameOf path'} or "missing"; + # Trick to check if the symlink target exists and is a directory: + # if we append a "/." to the string version of the path, Nix won't + # canocalize it (which would strip any "/." in the path), so if + # path' + "/." exists, we know that the symlink points to an existing + # directory. If not, either the target doesn't exist or is a regular file. + # TODO(sterni): is there a way to check reliably if the symlink target exists? + isSymlinkDir = builtins.pathExists (path' + "/."); + in { + ${thisPathType} = + /**/ if thisPathType != "symlink" then true + else if isSymlinkDir then "directory" + else "regular-or-missing"; + }; + + pathType' = path: + let + p = pathType path; + in + if p ? missing + then builtins.throw "${lib.generators.toPretty {} path} does not exist" + else p; + + /* Check whether the given path is a directory. + Throws if the path in question doesn't exist. + + Type: path(-like) -> bool + */ + isDirectory = path: pathType' path ? directory; + + /* Checks whether the given path is a directory or + a symlink to a directory. Throws if the path in + question doesn't exist. + + Warning: Does not throw if the target file or + directory doesn't exist, but the symlink does. + + Type: path(-like) -> bool + */ + realPathIsDirectory = path: let + pt = pathType' path; + in pt ? directory || pt.symlink or null == "directory"; + + /* Check whether the given path is a regular file. + Throws if the path in question doesn't exist. + + Type: path(-like) -> bool + */ + isRegularFile = path: pathType' path ? regular; + + /* Check whether the given path is a symbolic link. + Throws if the path in question doesn't exist. + + Type: path(-like) -> bool + */ + isSymlink = path: pathType' path ? symlink; + +in { + inherit + storePathName + pathType + isDirectory + realPathIsDirectory + isRegularFile + isSymlink + ; +} |