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Document fetchClosure
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@ -4,3 +4,10 @@
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* `nix store make-content-addressable` has been renamed to `nix store
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make-content-addressed`.
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* New builtin function `builtins.fetchClosure` that copies a closure
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from a binary cache at evaluation time and rewrites it to
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content-addressed form (if it isn't already). Like
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`builtins.storePath`, this allows importing pre-built store paths;
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the difference is that it doesn't require the user to configure
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binary caches and trusted public keys.
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@ -110,6 +110,39 @@ static RegisterPrimOp primop_fetchClosure({
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.name = "__fetchClosure",
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.args = {"args"},
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.doc = R"(
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Fetch a Nix store closure from a binary cache, rewriting it into
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content-addressed form. For example,
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```nix
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builtins.fetchClosure {
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fromStore = "https://cache.nixos.org";
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fromPath = /nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1;
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toPath = /nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1;
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}
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```
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fetches `/nix/store/r2jd...` from the specified binary cache,
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and rewrites it into the content-addressed store path
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`/nix/store/ldbh...`.
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If `fromPath` is already content-addressed, or if you are
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allowing impure evaluation (`--impure`), then `toPath` may be
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omitted.
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To find out the correct value for `toPath` given a `fromPath`,
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you can use `nix store make-content-addressed`:
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```console
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# nix store make-content-addressed /nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1
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rewrote '/nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1' to '/nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1'
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```
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This function is similar to `builtins.storePath` in that it
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allows you to use a previously built store path in a Nix
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expression. However, it is more reproducible because it requires
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specifying a binary cache from which the path can be fetched.
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Also, requiring a content-addressed final store path avoids the
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need for users to configure binary cache public keys.
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)",
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.fun = prim_fetchClosure,
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});
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