nixpkgs/lib/path/default.nix

561 lines
18 KiB
Nix

/* Functions for working with path values. */
# See ./README.md for internal docs
{ lib }:
let
inherit (builtins)
isString
isPath
split
match
typeOf
;
inherit (lib.lists)
length
head
last
genList
elemAt
all
concatMap
foldl'
take
drop
;
inherit (lib.strings)
concatStringsSep
substring
;
inherit (lib.asserts)
assertMsg
;
inherit (lib.path.subpath)
isValid
;
# Return the reason why a subpath is invalid, or `null` if it's valid
subpathInvalidReason = value:
if ! isString value then
"The given value is of type ${builtins.typeOf value}, but a string was expected"
else if value == "" then
"The given string is empty"
else if substring 0 1 value == "/" then
"The given string \"${value}\" starts with a `/`, representing an absolute path"
# We don't support ".." components, see ./path.md#parent-directory
else if match "(.*/)?\\.\\.(/.*)?" value != null then
"The given string \"${value}\" contains a `..` component, which is not allowed in subpaths"
else null;
# Split and normalise a relative path string into its components.
# Error for ".." components and doesn't include "." components
splitRelPath = path:
let
# Split the string into its parts using regex for efficiency. This regex
# matches patterns like "/", "/./", "/././", with arbitrarily many "/"s
# together. These are the main special cases:
# - Leading "./" gets split into a leading "." part
# - Trailing "/." or "/" get split into a trailing "." or ""
# part respectively
#
# These are the only cases where "." and "" parts can occur
parts = split "/+(\\./+)*" path;
# `split` creates a list of 2 * k + 1 elements, containing the k +
# 1 parts, interleaved with k matches where k is the number of
# (non-overlapping) matches. This calculation here gets the number of parts
# back from the list length
# floor( (2 * k + 1) / 2 ) + 1 == floor( k + 1/2 ) + 1 == k + 1
partCount = length parts / 2 + 1;
# To assemble the final list of components we want to:
# - Skip a potential leading ".", normalising "./foo" to "foo"
# - Skip a potential trailing "." or "", normalising "foo/" and "foo/." to
# "foo". See ./path.md#trailing-slashes
skipStart = if head parts == "." then 1 else 0;
skipEnd = if last parts == "." || last parts == "" then 1 else 0;
# We can now know the length of the result by removing the number of
# skipped parts from the total number
componentCount = partCount - skipEnd - skipStart;
in
# Special case of a single "." path component. Such a case leaves a
# componentCount of -1 due to the skipStart/skipEnd not verifying that
# they don't refer to the same character
if path == "." then []
# Generate the result list directly. This is more efficient than a
# combination of `filter`, `init` and `tail`, because here we don't
# allocate any intermediate lists
else genList (index:
# To get to the element we need to add the number of parts we skip and
# multiply by two due to the interleaved layout of `parts`
elemAt parts ((skipStart + index) * 2)
) componentCount;
# Join relative path components together
joinRelPath = components:
# Always return relative paths with `./` as a prefix (./path.md#leading-dots-for-relative-paths)
"./" +
# An empty string is not a valid relative path, so we need to return a `.` when we have no components
(if components == [] then "." else concatStringsSep "/" components);
# Type: Path -> { root :: Path, components :: [ String ] }
#
# Deconstruct a path value type into:
# - root: The filesystem root of the path, generally `/`
# - components: All the path's components
#
# This is similar to `splitString "/" (toString path)` but safer
# because it can distinguish different filesystem roots
deconstructPath =
let
recurse = components: base:
# If the parent of a path is the path itself, then it's a filesystem root
if base == dirOf base then { root = base; inherit components; }
else recurse ([ (baseNameOf base) ] ++ components) (dirOf base);
in recurse [];
in /* No rec! Add dependencies on this file at the top. */ {
/*
Append a subpath string to a path.
Like `path + ("/" + string)` but safer, because it errors instead of returning potentially surprising results.
More specifically, it checks that the first argument is a [path value type](https://nixos.org/manual/nix/stable/language/values.html#type-path"),
and that the second argument is a [valid subpath string](#function-library-lib.path.subpath.isValid).
Laws:
- Not influenced by subpath [normalisation](#function-library-lib.path.subpath.normalise):
append p s == append p (subpath.normalise s)
Type:
append :: Path -> String -> Path
Example:
append /foo "bar/baz"
=> /foo/bar/baz
# subpaths don't need to be normalised
append /foo "./bar//baz/./"
=> /foo/bar/baz
# can append to root directory
append /. "foo/bar"
=> /foo/bar
# first argument needs to be a path value type
append "/foo" "bar"
=> <error>
# second argument needs to be a valid subpath string
append /foo /bar
=> <error>
append /foo ""
=> <error>
append /foo "/bar"
=> <error>
append /foo "../bar"
=> <error>
*/
append =
# The absolute path to append to
path:
# The subpath string to append
subpath:
assert assertMsg (isPath path) ''
lib.path.append: The first argument is of type ${builtins.typeOf path}, but a path was expected'';
assert assertMsg (isValid subpath) ''
lib.path.append: Second argument is not a valid subpath string:
${subpathInvalidReason subpath}'';
path + ("/" + subpath);
/*
Whether the first path is a component-wise prefix of the second path.
Laws:
- `hasPrefix p q` is only true if [`q == append p s`](#function-library-lib.path.append) for some [subpath](#function-library-lib.path.subpath.isValid) `s`.
- `hasPrefix` is a [non-strict partial order](https://en.wikipedia.org/wiki/Partially_ordered_set#Non-strict_partial_order) over the set of all path values.
Type:
hasPrefix :: Path -> Path -> Bool
Example:
hasPrefix /foo /foo/bar
=> true
hasPrefix /foo /foo
=> true
hasPrefix /foo/bar /foo
=> false
hasPrefix /. /foo
=> true
*/
hasPrefix =
path1:
assert assertMsg
(isPath path1)
"lib.path.hasPrefix: First argument is of type ${typeOf path1}, but a path was expected";
let
path1Deconstructed = deconstructPath path1;
in
path2:
assert assertMsg
(isPath path2)
"lib.path.hasPrefix: Second argument is of type ${typeOf path2}, but a path was expected";
let
path2Deconstructed = deconstructPath path2;
in
assert assertMsg
(path1Deconstructed.root == path2Deconstructed.root) ''
lib.path.hasPrefix: Filesystem roots must be the same for both paths, but paths with different roots were given:
first argument: "${toString path1}" with root "${toString path1Deconstructed.root}"
second argument: "${toString path2}" with root "${toString path2Deconstructed.root}"'';
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](#function-library-lib.path.subpath.normalise).
Laws:
- Inverts [`append`](#function-library-lib.path.append) for [normalised subpath string](#function-library-lib.path.subpath.normalise):
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;
/*
Split the filesystem root from a [path](https://nixos.org/manual/nix/stable/language/values.html#type-path).
The result is an attribute set with these attributes:
- `root`: The filesystem root of the path, meaning that this directory has no parent directory.
- `subpath`: The [normalised subpath string](#function-library-lib.path.subpath.normalise) that when [appended](#function-library-lib.path.append) to `root` returns the original path.
Laws:
- [Appending](#function-library-lib.path.append) the `root` and `subpath` gives the original path:
p ==
append
(splitRoot p).root
(splitRoot p).subpath
- Trying to get the parent directory of `root` using [`readDir`](https://nixos.org/manual/nix/stable/language/builtins.html#builtins-readDir) returns `root` itself:
dirOf (splitRoot p).root == (splitRoot p).root
Type:
splitRoot :: Path -> { root :: Path, subpath :: String }
Example:
splitRoot /foo/bar
=> { root = /.; subpath = "./foo/bar"; }
splitRoot /.
=> { root = /.; subpath = "./."; }
# Nix neutralises `..` path components for all path values automatically
splitRoot /foo/../bar
=> { root = /.; subpath = "./bar"; }
splitRoot "/foo/bar"
=> <error>
*/
splitRoot =
# The path to split the root off of
path:
assert assertMsg
(isPath path)
"lib.path.splitRoot: Argument is of type ${typeOf path}, but a path was expected";
let
deconstructed = deconstructPath path;
in {
root = deconstructed.root;
subpath = joinRelPath deconstructed.components;
};
/*
Whether a value is a valid subpath string.
A subpath string points to a specific file or directory within an absolute base directory.
It is a stricter form of a relative path that excludes `..` components, since those could escape the base directory.
- The value is a string.
- The string is not empty.
- The string doesn't start with a `/`.
- The string doesn't contain any `..` path components.
Type:
subpath.isValid :: String -> Bool
Example:
# Not a string
subpath.isValid null
=> false
# Empty string
subpath.isValid ""
=> false
# Absolute path
subpath.isValid "/foo"
=> false
# Contains a `..` path component
subpath.isValid "../foo"
=> false
# Valid subpath
subpath.isValid "foo/bar"
=> true
# Doesn't need to be normalised
subpath.isValid "./foo//bar/"
=> true
*/
subpath.isValid =
# The value to check
value:
subpathInvalidReason value == null;
/*
Join subpath strings together using `/`, returning a normalised subpath string.
Like `concatStringsSep "/"` but safer, specifically:
- All elements must be [valid subpath strings](#function-library-lib.path.subpath.isValid).
- The result gets [normalised](#function-library-lib.path.subpath.normalise).
- The edge case of an empty list gets properly handled by returning the neutral subpath `"./."`.
Laws:
- Associativity:
subpath.join [ x (subpath.join [ y z ]) ] == subpath.join [ (subpath.join [ x y ]) z ]
- Identity - `"./."` is the neutral element for normalised paths:
subpath.join [ ] == "./."
subpath.join [ (subpath.normalise p) "./." ] == subpath.normalise p
subpath.join [ "./." (subpath.normalise p) ] == subpath.normalise p
- Normalisation - the result is [normalised](#function-library-lib.path.subpath.normalise):
subpath.join ps == subpath.normalise (subpath.join ps)
- For non-empty lists, the implementation is equivalent to [normalising](#function-library-lib.path.subpath.normalise) the result of `concatStringsSep "/"`.
Note that the above laws can be derived from this one:
ps != [] -> subpath.join ps == subpath.normalise (concatStringsSep "/" ps)
Type:
subpath.join :: [ String ] -> String
Example:
subpath.join [ "foo" "bar/baz" ]
=> "./foo/bar/baz"
# normalise the result
subpath.join [ "./foo" "." "bar//./baz/" ]
=> "./foo/bar/baz"
# passing an empty list results in the current directory
subpath.join [ ]
=> "./."
# elements must be valid subpath strings
subpath.join [ /foo ]
=> <error>
subpath.join [ "" ]
=> <error>
subpath.join [ "/foo" ]
=> <error>
subpath.join [ "../foo" ]
=> <error>
*/
subpath.join =
# The list of subpaths to join together
subpaths:
# Fast in case all paths are valid
if all isValid subpaths
then joinRelPath (concatMap splitRelPath subpaths)
else
# Otherwise we take our time to gather more info for a better error message
# Strictly go through each path, throwing on the first invalid one
# Tracks the list index in the fold accumulator
foldl' (i: path:
if isValid path
then i + 1
else throw ''
lib.path.subpath.join: Element at index ${toString i} is not a valid subpath string:
${subpathInvalidReason path}''
) 0 subpaths;
/*
Split [a subpath](#function-library-lib.path.subpath.isValid) into its path component strings.
Throw an error if the subpath isn't valid.
Note that the returned path components are also [valid subpath strings](#function-library-lib.path.subpath.isValid), though they are intentionally not [normalised](#function-library-lib.path.subpath.normalise).
Laws:
- Splitting a subpath into components and [joining](#function-library-lib.path.subpath.join) the components gives the same subpath but [normalised](#function-library-lib.path.subpath.normalise):
subpath.join (subpath.components s) == subpath.normalise s
Type:
subpath.components :: String -> [ String ]
Example:
subpath.components "."
=> [ ]
subpath.components "./foo//bar/./baz/"
=> [ "foo" "bar" "baz" ]
subpath.components "/foo"
=> <error>
*/
subpath.components =
# The subpath string to split into components
subpath:
assert assertMsg (isValid subpath) ''
lib.path.subpath.components: Argument is not a valid subpath string:
${subpathInvalidReason subpath}'';
splitRelPath subpath;
/*
Normalise a subpath. Throw an error if the subpath isn't [valid](#function-library-lib.path.subpath.isValid).
- Limit repeating `/` to a single one.
- Remove redundant `.` components.
- Remove trailing `/` and `/.`.
- Add leading `./`.
Laws:
- Idempotency - normalising multiple times gives the same result:
subpath.normalise (subpath.normalise p) == subpath.normalise p
- Uniqueness - there's only a single normalisation for the paths that lead to the same file system node:
subpath.normalise p != subpath.normalise q -> $(realpath ${p}) != $(realpath ${q})
- Don't change the result when [appended](#function-library-lib.path.append) to a Nix path value:
append base p == append base (subpath.normalise p)
- Don't change the path according to `realpath`:
$(realpath ${p}) == $(realpath ${subpath.normalise p})
- Only error on [invalid subpaths](#function-library-lib.path.subpath.isValid):
builtins.tryEval (subpath.normalise p)).success == subpath.isValid p
Type:
subpath.normalise :: String -> String
Example:
# limit repeating `/` to a single one
subpath.normalise "foo//bar"
=> "./foo/bar"
# remove redundant `.` components
subpath.normalise "foo/./bar"
=> "./foo/bar"
# add leading `./`
subpath.normalise "foo/bar"
=> "./foo/bar"
# remove trailing `/`
subpath.normalise "foo/bar/"
=> "./foo/bar"
# remove trailing `/.`
subpath.normalise "foo/bar/."
=> "./foo/bar"
# Return the current directory as `./.`
subpath.normalise "."
=> "./."
# error on `..` path components
subpath.normalise "foo/../bar"
=> <error>
# error on empty string
subpath.normalise ""
=> <error>
# error on absolute path
subpath.normalise "/foo"
=> <error>
*/
subpath.normalise =
# The subpath string to normalise
subpath:
assert assertMsg (isValid subpath) ''
lib.path.subpath.normalise: Argument is not a valid subpath string:
${subpathInvalidReason subpath}'';
joinRelPath (splitRelPath subpath);
}