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Merge pull request #257356 from tweag/fileset.intersect

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`lib.fileset.intersection`: init
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Silvan Mosberger 2023-10-11 17:33:32 +02:00 committed by GitHub
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35
lib/fileset/README.md
View file

@ -58,7 +58,8 @@ An attribute set with these values:
- `_internalBase` (path):
Any files outside of this path cannot influence the set of files.
This is always a directory.
This is always a directory and should be as long as possible.
This is used by `lib.fileset.toSource` to check that all files are under the `root` argument
- `_internalBaseRoot` (path):
The filesystem root of `_internalBase`, same as `(lib.path.splitRoot _internalBase).root`.
@ -143,9 +144,37 @@ Arguments:
- (-) Leaves us with no identity element for `union` and no reasonable return value for `unions []`.
From a set theory perspective, which has a well-known notion of empty sets, this is unintuitive.
### No intersection for lists
While there is `intersection a b`, there is no function `intersections [ a b c ]`.
Arguments:
- (+) There is no known use case for such a function, it can be added later if a use case arises
- (+) There is no suitable return value for `intersections [ ]`, see also "Nullary intersections" [here](https://en.wikipedia.org/w/index.php?title=List_of_set_identities_and_relations&oldid=1177174035#Definitions)
- (-) Could throw an error for that case
- (-) Create a special value to represent "all the files" and return that
- (+) Such a value could then not be used with `fileFilter` unless the internal representation is changed considerably
- (-) Could return the empty file set
- (+) This would be wrong in set theory
- (-) Inconsistent with `union` and `unions`
### Intersection base path
The base path of the result of an `intersection` is the longest base path of the arguments.
E.g. the base path of `intersection ./foo ./foo/bar` is `./foo/bar`.
Meanwhile `intersection ./foo ./bar` returns the empty file set without a base path.
Arguments:
- Alternative: Use the common prefix of all base paths as the resulting base path
- (-) This is unnecessarily strict, because the purpose of the base path is to track the directory under which files _could_ be in the file set. It should be as long as possible.
All files contained in `intersection ./foo ./foo/bar` will be under `./foo/bar` (never just under `./foo`), and `intersection ./foo ./bar` will never contain any files (never under `./.`).
This would lead to `toSource` having to unexpectedly throw errors for cases such as `toSource { root = ./foo; fileset = intersect ./foo base; }`, where `base` may be `./bar` or `./.`.
- (-) There is no benefit to the user, since base path is not directly exposed in the interface
### Empty directories
File sets can only represent a _set_ of local files, directories on their own are not representable.
File sets can only represent a _set_ of local files.
Directories on their own are not representable.
Arguments:
- (+) There does not seem to be a sensible set of combinators when directories can be represented on their own.
@ -161,7 +190,7 @@ Arguments:
- `./.` represents all files in `./.` _and_ the directory itself, but not its subdirectories, meaning that at least `./.` will be preserved even if it's empty.
In that case, `intersect ./. ./foo` should only include files and no directories themselves, since `./.` includes only `./.` as a directory, and same for `./foo`, so there's no overlap in directories.
In that case, `intersection ./. ./foo` should only include files and no directories themselves, since `./.` includes only `./.` as a directory, and same for `./foo`, so there's no overlap in directories.
But intuitively this operation should result in the same as `./foo` – everything else is just confusing.
- (+) This matches how Git only supports files, so developers should already be used to it.
- (-) Empty directories (even if they contain nested directories) are neither representable nor preserved when coercing from paths.

41
lib/fileset/default.nix
View file

@ -7,6 +7,7 @@ let
_toSourceFilter
_unionMany
_printFileset
_intersection
;
inherit (builtins)
@ -18,6 +19,7 @@ let
;
inherit (lib.lists)
elemAt
imap0
;
@ -276,6 +278,45 @@ If a directory does not recursively contain any file, it is omitted from the sto
_unionMany
];
/*
The file set containing all files that are in both of two given file sets.
See also [Intersection (set theory)](https://en.wikipedia.org/wiki/Intersection_(set_theory)).
The given file sets are evaluated as lazily as possible,
with the first argument being evaluated first if needed.
Type:
intersection :: FileSet -> FileSet -> FileSet
Example:
# Limit the selected files to the ones in ./., so only ./src and ./Makefile
intersection ./. (unions [ ../LICENSE ./src ./Makefile ])
*/
intersection =
# The first file set.
# This argument can also be a path,
# which gets [implicitly coerced to a file set](#sec-fileset-path-coercion).
fileset1:
# The second file set.
# This argument can also be a path,
# which gets [implicitly coerced to a file set](#sec-fileset-path-coercion).
fileset2:
let
filesets = _coerceMany "lib.fileset.intersection" [
{
context = "first argument";
value = fileset1;
}
{
context = "second argument";
value = fileset2;
}
];
in
_intersection
(elemAt filesets 0)
(elemAt filesets 1);
/*
Incrementally evaluate and trace a file set in a pretty way.
This function is only intended for debugging purposes.

115
lib/fileset/internal.nix
View file

@ -461,6 +461,43 @@ rec {
else
nonEmpty;
# Transforms the filesetTree of a file set to a shorter base path, e.g.
# _shortenTreeBase [ "foo" ] (_create /foo/bar null)
# => { bar = null; }
_shortenTreeBase = targetBaseComponents: fileset:
let
recurse = index:
# If we haven't reached the required depth yet
if index < length fileset._internalBaseComponents then
# Create an attribute set and recurse as the value, this can be lazily evaluated this way
{ ${elemAt fileset._internalBaseComponents index} = recurse (index + 1); }
else
# Otherwise we reached the appropriate depth, here's the original tree
fileset._internalTree;
in
recurse (length targetBaseComponents);
# Transforms the filesetTree of a file set to a longer base path, e.g.
# _lengthenTreeBase [ "foo" "bar" ] (_create /foo { bar.baz = "regular"; })
# => { baz = "regular"; }
_lengthenTreeBase = targetBaseComponents: fileset:
let
recurse = index: tree:
# If the filesetTree is an attribute set and we haven't reached the required depth yet
if isAttrs tree && index < length targetBaseComponents then
# Recurse with the tree under the right component (which might not exist)
recurse (index + 1) (tree.${elemAt targetBaseComponents index} or null)
else
# For all values here we can just return the tree itself:
# tree == null -> the result is also null, everything is excluded
# tree == "directory" -> the result is also "directory",
# because the base path is always a directory and everything is included
# isAttrs tree -> the result is `tree`
# because we don't need to recurse any more since `index == length longestBaseComponents`
tree;
in
recurse (length fileset._internalBaseComponents) fileset._internalTree;
# Computes the union of a list of filesets.
# The filesets must already be coerced and validated to be in the same filesystem root
# Type: [ Fileset ] -> Fileset
@ -497,11 +534,7 @@ rec {
# So the tree under `/foo/bar` gets nested under `{ bar = ...; ... }`,
# while the tree under `/foo/baz` gets nested under `{ baz = ...; ... }`
# Therefore allowing combined operations over them.
trees = map (fileset:
setAttrByPath
(drop (length commonBaseComponents) fileset._internalBaseComponents)
fileset._internalTree
) filesetsWithBase;
trees = map (_shortenTreeBase commonBaseComponents) filesetsWithBase;
# Folds all trees together into a single one using _unionTree
# We do not use a fold here because it would cause a thunk build-up
@ -533,4 +566,76 @@ rec {
# The non-null elements have to be attribute sets representing partial trees
# We need to recurse into those
zipAttrsWith (name: _unionTrees) withoutNull;
# Computes the intersection of a list of filesets.
# The filesets must already be coerced and validated to be in the same filesystem root
# Type: Fileset -> Fileset -> Fileset
_intersection = fileset1: fileset2:
let
# The common base components prefix, e.g.
# (/foo/bar, /foo/bar/baz) -> /foo/bar
# (/foo/bar, /foo/baz) -> /foo
commonBaseComponentsLength =
# TODO: Have a `lib.lists.commonPrefixLength` function such that we don't need the list allocation from commonPrefix here
length (
commonPrefix
fileset1._internalBaseComponents
fileset2._internalBaseComponents
);
# To be able to intersect filesetTree's together, they need to have the same base path.
# Base paths can be intersected by taking the longest one (if any)
# The fileset with the longest base, if any, e.g.
# (/foo/bar, /foo/bar/baz) -> /foo/bar/baz
# (/foo/bar, /foo/baz) -> null
longestBaseFileset =
if commonBaseComponentsLength == length fileset1._internalBaseComponents then
# The common prefix is the same as the first path, so the second path is equal or longer
fileset2
else if commonBaseComponentsLength == length fileset2._internalBaseComponents then
# The common prefix is the same as the second path, so the first path is longer
fileset1
else
# The common prefix is neither the first nor the second path
# This means there's no overlap between the two sets
null;
# Whether the result should be the empty value without a base
resultIsEmptyWithoutBase =
# If either fileset is the empty fileset without a base, the intersection is too
fileset1._internalIsEmptyWithoutBase
|| fileset2._internalIsEmptyWithoutBase
# If there is no overlap between the base paths
|| longestBaseFileset == null;
# Lengthen each fileset's tree to the longest base prefix
tree1 = _lengthenTreeBase longestBaseFileset._internalBaseComponents fileset1;
tree2 = _lengthenTreeBase longestBaseFileset._internalBaseComponents fileset2;
# With two filesetTree's with the same base, we can compute their intersection
resultTree = _intersectTree tree1 tree2;
in
if resultIsEmptyWithoutBase then
_emptyWithoutBase
else
_create longestBaseFileset._internalBase resultTree;
# The intersection of two filesetTree's with the same base path
# The second element is only evaluated as much as necessary.
# Type: filesetTree -> filesetTree -> filesetTree
_intersectTree = lhs: rhs:
if isAttrs lhs && isAttrs rhs then
# Both sides are attribute sets, we can recurse for the attributes existing on both sides
mapAttrs
(name: _intersectTree lhs.${name})
(builtins.intersectAttrs lhs rhs)
else if lhs == null || isString rhs then
# If the lhs is null, the result should also be null
# And if the rhs is the identity element
# (a string, aka it includes everything), then it's also the lhs
lhs
else
# In all other cases it's the rhs
rhs;
}

95
lib/fileset/tests.sh
View file

@ -587,6 +587,97 @@ done
# So, just using 1000 files for now.
checkFileset 'unions (mapAttrsToList (name: _: ./. + "/${name}/a") (builtins.readDir ./.))'
## lib.fileset.intersection
# Different filesystem roots in root and fileset are not supported
mkdir -p {foo,bar}/mock-root
expectFailure 'with ((import <nixpkgs/lib>).extend (import <nixpkgs/lib/fileset/mock-splitRoot.nix>)).fileset;
toSource { root = ./.; fileset = intersection ./foo/mock-root ./bar/mock-root; }
' 'lib.fileset.intersection: Filesystem roots are not the same:
\s*first argument: root "'"$work"'/foo/mock-root"
\s*second argument: root "'"$work"'/bar/mock-root"
\s*Different roots are not supported.'
rm -rf -- *
# Coercion errors show the correct context
expectFailure 'toSource { root = ./.; fileset = intersection ./a ./.; }' 'lib.fileset.intersection: first argument \('"$work"'/a\) does not exist.'
expectFailure 'toSource { root = ./.; fileset = intersection ./. ./b; }' 'lib.fileset.intersection: second argument \('"$work"'/b\) does not exist.'
# The tree of later arguments should not be evaluated if a former argument already excludes all files
tree=(
[a]=0
)
checkFileset 'intersection _emptyWithoutBase (_create ./. (abort "This should not be used!"))'
# We don't have any combinators that can explicitly remove files yet, so we need to rely on internal functions to test this for now
checkFileset 'intersection (_create ./. { a = null; }) (_create ./. { a = abort "This should not be used!"; })'
# If either side is empty, the result is empty
tree=(
[a]=0
)
checkFileset 'intersection _emptyWithoutBase _emptyWithoutBase'
checkFileset 'intersection _emptyWithoutBase (_create ./. null)'
checkFileset 'intersection (_create ./. null) _emptyWithoutBase'
checkFileset 'intersection (_create ./. null) (_create ./. null)'
# If the intersection base paths are not overlapping, the result is empty and has no base path
mkdir a b c
touch {a,b,c}/x
expectEqual 'toSource { root = ./c; fileset = intersection ./a ./b; }' 'toSource { root = ./c; fileset = _emptyWithoutBase; }'
rm -rf -- *
# If the intersection exists, the resulting base path is the longest of them
mkdir a
touch x a/b
expectEqual 'toSource { root = ./a; fileset = intersection ./a ./.; }' 'toSource { root = ./a; fileset = ./a; }'
expectEqual 'toSource { root = ./a; fileset = intersection ./. ./a; }' 'toSource { root = ./a; fileset = ./a; }'
rm -rf -- *
# Also finds the intersection with null'd filesetTree's
tree=(
[a]=0
[b]=1
[c]=0
)
checkFileset 'intersection (_create ./. { a = "regular"; b = "regular"; c = null; }) (_create ./. { a = null; b = "regular"; c = "regular"; })'
# Actually computes the intersection between files
tree=(
[a]=0
[b]=0
[c]=1
[d]=1
[e]=0
[f]=0
)
checkFileset 'intersection (unions [ ./a ./b ./c ./d ]) (unions [ ./c ./d ./e ./f ])'
tree=(
[a/x]=0
[a/y]=0
[b/x]=1
[b/y]=1
[c/x]=0
[c/y]=0
)
checkFileset 'intersection ./b ./.'
checkFileset 'intersection ./b (unions [ ./a/x ./a/y ./b/x ./b/y ./c/x ./c/y ])'
# Complicated case
tree=(
[a/x]=0
[a/b/i]=1
[c/d/x]=0
[c/d/f]=1
[c/x]=0
[c/e/i]=1
[c/e/j]=1
)
checkFileset 'intersection (unions [ ./a/b ./c/d ./c/e ]) (unions [ ./a ./c/d/f ./c/e ])'
## Tracing
# The second trace argument is returned
@ -609,6 +700,10 @@ rm -rf -- *
# The empty file set without a base also prints as empty
expectTrace '_emptyWithoutBase' '(empty)'
expectTrace 'unions [ ]' '(empty)'
mkdir foo bar
touch {foo,bar}/x
expectTrace 'intersection ./foo ./bar' '(empty)'
rm -rf -- *
# If a directory is fully included, print it as such
touch a