23dd8067c5
Given a path (which points to a directory and a list of paths which
are below that path, build a “sparse” version of that directory, so
that it only contains the listed paths (and their children):
$ nix-build -E 'with import ./. {}; nix.sparseTree ./. [
./default.nix
./nix/readTree
./nix/buildLisp
./third_party/nixpkgs
./third_party/overlays
]'
/nix/store/0ynj0gc613fs6mfp9snqcvdj5gfxbdzg-sparse-depot
$ lr -t 'type == d' result/
result/
result/nix
result/nix/buildLisp
result/nix/buildLisp/example
result/nix/readTree
result/nix/readTree/tests
[…]
result/third_party
result/third_party/nixpkgs
result/third_party/overlays
result/third_party/overlays/haskell
result/third_party/overlays/haskell/patches
result/third_party/overlays/patches
This is useful if a derivation depends on depot.path (e. g. if it wants
to import depot at runtime). Usually this means that on every depot
commit (or even worse, every change of .git on a local machine), this
derivation has to be rebuild. By using sparseTree you can instead depend
on a stripped down version of depot which only contains the bits you
actually depend on, avoiding unrelated rebuilds.
Change-Id: I127b108c8b177c657fb46786d0a6256516fd2c52
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3503
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
62 lines
1.8 KiB
Nix
62 lines
1.8 KiB
Nix
# Build a “sparse” version of a given directory, only including contained files
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# and directories if they are listed in a supplied list:
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#
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# # A very minimal depot
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# sparseTree ./depot [
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# ./default.nix
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# ./depot/nix/readTree/default.nix
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# ./third_party/nixpkgs
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# ./third_party/overlays
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# ]
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{ pkgs, lib, ... }:
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# root path to use as a reference point
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root:
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# list of paths below `root` that should be
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# included in the resulting directory
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paths:
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let
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rootLength = builtins.stringLength (toString root);
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# Count slashes in a path.
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#
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# Type: path -> int
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depth = path: lib.pipe path [
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toString
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(builtins.split "/")
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(builtins.filter builtins.isList)
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builtins.length
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];
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# (Parent) directories will be created from deepest to shallowest
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# which should mean no conflicts are caused unless both a child
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# and its parent directory are in the list of paths.
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# TODO(sterni): improve error messages in such cases
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fromDeepest = lib.sort (a: b: depth a < depth b) paths;
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# Create a set which contains the source path to copy / symlink and
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# it's destination, so the path below the destination root including
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# a leading slash. Additionally some sanity checking is done.
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makeSymlink = path:
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let
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strPath = toString path;
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contextPath = "${path}";
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belowRoot = builtins.substring rootLength (-1) strPath;
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prefix = builtins.substring 0 rootLength strPath;
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in assert toString root == prefix; {
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src = contextPath;
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dst = belowRoot;
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};
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symlinks = builtins.map makeSymlink fromDeepest;
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in
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# TODO(sterni): teach readTree to also read symlinked directories,
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# so we ln -sT instead of cp -aT.
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pkgs.runCommandNoCC "sparse-${builtins.baseNameOf root}" {} (
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lib.concatMapStrings ({ src, dst }: ''
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mkdir -p "$(dirname "$out${dst}")"
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cp -aT --reflink=auto "${src}" "$out${dst}"
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'') symlinks
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)
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