lib.fileset.difference: init
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Silvan Mosberger
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3 changed files with 231 additions and 0 deletions
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@ -9,6 +9,7 @@ let
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_fileFilter
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_printFileset
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_intersection
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_difference
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;
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inherit (builtins)
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@ -368,6 +369,58 @@ If a directory does not recursively contain any file, it is omitted from the sto
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(elemAt filesets 0)
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(elemAt filesets 1);
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/*
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The file set containing all files from the first file set that are not in the second file set.
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See also [Difference (set theory)](https://en.wikipedia.org/wiki/Complement_(set_theory)#Relative_complement).
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The given file sets are evaluated as lazily as possible,
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with the first argument being evaluated first if needed.
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Type:
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union :: FileSet -> FileSet -> FileSet
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Example:
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# Create a file set containing all files from the current directory,
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# except ones under ./tests
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difference ./. ./tests
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let
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# A set of Nix-related files
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nixFiles = unions [ ./default.nix ./nix ./tests/default.nix ];
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in
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# Create a file set containing all files under ./tests, except ones in `nixFiles`,
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# meaning only without ./tests/default.nix
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difference ./tests nixFiles
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*/
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difference =
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# The positive file set.
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# The result can only contain files that are also in this file set.
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#
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# This argument can also be a path,
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# which gets [implicitly coerced to a file set](#sec-fileset-path-coercion).
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positive:
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# The negative file set.
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# The result will never contain files that are also in this file set.
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#
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# This argument can also be a path,
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# which gets [implicitly coerced to a file set](#sec-fileset-path-coercion).
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negative:
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let
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filesets = _coerceMany "lib.fileset.difference" [
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{
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context = "first argument (positive set)";
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value = positive;
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}
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{
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context = "second argument (negative set)";
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value = negative;
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}
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];
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in
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_difference
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(elemAt filesets 0)
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(elemAt filesets 1);
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/*
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Incrementally evaluate and trace a file set in a pretty way.
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This function is only intended for debugging purposes.
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@ -639,6 +639,86 @@ rec {
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# In all other cases it's the rhs
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rhs;
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# Compute the set difference between two file sets.
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# The filesets must already be coerced and validated to be in the same filesystem root.
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# Type: Fileset -> Fileset -> Fileset
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_difference = positive: negative:
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let
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# The common base components prefix, e.g.
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# (/foo/bar, /foo/bar/baz) -> /foo/bar
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# (/foo/bar, /foo/baz) -> /foo
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commonBaseComponentsLength =
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# TODO: Have a `lib.lists.commonPrefixLength` function such that we don't need the list allocation from commonPrefix here
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length (
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commonPrefix
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positive._internalBaseComponents
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negative._internalBaseComponents
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);
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# We need filesetTree's with the same base to be able to compute the difference between them
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# This here is the filesetTree from the negative file set, but for a base path that matches the positive file set.
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# Examples:
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# For `difference /foo /foo/bar`, `negativeTreeWithPositiveBase = { bar = "directory"; }`
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# because under the base path of `/foo`, only `bar` from the negative file set is included
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# For `difference /foo/bar /foo`, `negativeTreeWithPositiveBase = "directory"`
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# because under the base path of `/foo/bar`, everything from the negative file set is included
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# For `difference /foo /bar`, `negativeTreeWithPositiveBase = null`
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# because under the base path of `/foo`, nothing from the negative file set is included
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negativeTreeWithPositiveBase =
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if commonBaseComponentsLength == length positive._internalBaseComponents then
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# The common prefix is the same as the positive base path, so the second path is equal or longer.
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# We need to _shorten_ the negative filesetTree to the same base path as the positive one
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# E.g. for `difference /foo /foo/bar` the common prefix is /foo, equal to the positive file set's base
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# So we need to shorten the base of the tree for the negative argument from /foo/bar to just /foo
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_shortenTreeBase positive._internalBaseComponents negative
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else if commonBaseComponentsLength == length negative._internalBaseComponents then
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# The common prefix is the same as the negative base path, so the first path is longer.
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# We need to lengthen the negative filesetTree to the same base path as the positive one.
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# E.g. for `difference /foo/bar /foo` the common prefix is /foo, equal to the negative file set's base
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# So we need to lengthen the base of the tree for the negative argument from /foo to /foo/bar
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_lengthenTreeBase positive._internalBaseComponents negative
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else
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# The common prefix is neither the first nor the second path.
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# This means there's no overlap between the two file sets,
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# and nothing from the negative argument should get removed from the positive one
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# E.g for `difference /foo /bar`, we remove nothing to get the same as `/foo`
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null;
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resultingTree =
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_differenceTree
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positive._internalBase
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positive._internalTree
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negativeTreeWithPositiveBase;
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in
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# If the first file set is empty, we can never have any files in the result
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if positive._internalIsEmptyWithoutBase then
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_emptyWithoutBase
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# If the second file set is empty, nothing gets removed, so the result is just the first file set
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else if negative._internalIsEmptyWithoutBase then
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positive
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else
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# We use the positive file set base for the result,
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# because only files from the positive side may be included,
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# which is what base path is for
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_create positive._internalBase resultingTree;
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# Computes the set difference of two filesetTree's
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# Type: Path -> filesetTree -> filesetTree
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_differenceTree = path: lhs: rhs:
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# If the lhs doesn't have any files, or the right hand side includes all files
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if lhs == null || isString rhs then
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# The result will always be empty
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null
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# If the right hand side has no files
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else if rhs == null then
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# The result is always the left hand side, because nothing gets removed
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lhs
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else
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# Otherwise we always have two attribute sets to recurse into
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mapAttrs (name: lhsValue:
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_differenceTree (path + "/${name}") lhsValue (rhs.${name} or null)
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) (_directoryEntries path lhs);
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_fileFilter = predicate: fileset:
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let
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recurse = path: tree:
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@ -677,6 +677,104 @@ tree=(
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)
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checkFileset 'intersection (unions [ ./a/b ./c/d ./c/e ]) (unions [ ./a ./c/d/f ./c/e ])'
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## Difference
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# Subtracting something from itself results in nothing
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tree=(
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[a]=0
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)
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checkFileset 'difference ./. ./.'
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# The tree of the second argument should not be evaluated if not needed
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checkFileset 'difference _emptyWithoutBase (_create ./. (abort "This should not be used!"))'
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checkFileset 'difference (_create ./. null) (_create ./. (abort "This should not be used!"))'
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# Subtracting nothing gives the same thing back
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tree=(
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[a]=1
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)
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checkFileset 'difference ./. _emptyWithoutBase'
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checkFileset 'difference ./. (_create ./. null)'
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# Subtracting doesn't influence the base path
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mkdir a b
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touch {a,b}/x
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expectEqual 'toSource { root = ./a; fileset = difference ./a ./b; }' 'toSource { root = ./a; fileset = ./a; }'
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rm -rf -- *
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# Also not the other way around
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mkdir a
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expectFailure 'toSource { root = ./a; fileset = difference ./. ./a; }' 'lib.fileset.toSource: `fileset` could contain files in '"$work"', which is not under the `root` \('"$work"'/a\). Potential solutions:
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\s*- Set `root` to '"$work"' or any directory higher up. This changes the layout of the resulting store path.
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\s*- Set `fileset` to a file set that cannot contain files outside the `root` \('"$work"'/a\). This could change the files included in the result.'
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rm -rf -- *
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# Difference actually works
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# We test all combinations of ./., ./a, ./a/x and ./b
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tree=(
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[a/x]=0
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[a/y]=0
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[b]=0
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[c]=0
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)
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checkFileset 'difference ./. ./.'
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checkFileset 'difference ./a ./.'
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checkFileset 'difference ./a/x ./.'
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checkFileset 'difference ./b ./.'
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checkFileset 'difference ./a ./a'
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checkFileset 'difference ./a/x ./a'
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checkFileset 'difference ./a/x ./a/x'
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checkFileset 'difference ./b ./b'
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tree=(
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[a/x]=0
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[a/y]=0
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[b]=1
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[c]=1
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)
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checkFileset 'difference ./. ./a'
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tree=(
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[a/x]=1
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[a/y]=1
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[b]=0
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[c]=0
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)
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checkFileset 'difference ./a ./b'
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tree=(
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[a/x]=1
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[a/y]=0
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[b]=0
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[c]=0
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)
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checkFileset 'difference ./a/x ./b'
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tree=(
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[a/x]=0
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[a/y]=1
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[b]=0
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[c]=0
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)
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checkFileset 'difference ./a ./a/x'
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tree=(
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[a/x]=0
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[a/y]=0
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[b]=1
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[c]=0
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)
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checkFileset 'difference ./b ./a'
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checkFileset 'difference ./b ./a/x'
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tree=(
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[a/x]=0
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[a/y]=1
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[b]=1
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[c]=1
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)
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checkFileset 'difference ./. ./a/x'
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tree=(
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[a/x]=1
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[a/y]=1
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[b]=0
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[c]=1
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)
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checkFileset 'difference ./. ./b'
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## File filter
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