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fetchClosure: Interleave the examples in the docs

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Robert Hensing 2023-07-07 11:40:40 +02:00
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73
src/libexpr/primops/fetchClosure.cc
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@ -211,11 +211,26 @@ static RegisterPrimOp primop_fetchClosure({
.name = "__fetchClosure",
.args = {"args"},
.doc = R"(
Fetch a store path [closure](@docroot@/glossary.md#gloss-closure) from a binary cache.
Fetch a store path [closure](@docroot@/glossary.md#gloss-closure) from a binary cache, and return the store path as a string with context.
This function can be used in three ways:
This function can be invoked in three ways, that we will discuss in order of preference.
- Fetch any store path and rewrite it to a fully content-addressed store path.
**Fetch a content-addressed store path**
Example:
```nix
builtins.fetchClosure {
fromStore = "https://cache.nixos.org";
fromPath = /nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1;
}
```
This is the simplest invocation, and it does not require the user of the expression to configure [`trusted-public-keys`](@docroot@/command-ref/conf-file.md#conf-trusted-public-keys) to ensure their authenticity.
If your store path is [input addressed](@docroot@/glossary.md#gloss-input-addressed-store-object) instead of content addressed, consider the other two invocations.
**Fetch any store path and rewrite it to a fully content-addressed store path**
Example:
@ -227,36 +242,11 @@ static RegisterPrimOp primop_fetchClosure({
}
```
- Fetch a content-addressed store path.
Example:
```nix
builtins.fetchClosure {
fromStore = "https://cache.nixos.org";
fromPath = /nix/store/ldbhlwhh39wha58rm61bkiiwm6j7211j-git-2.33.1;
}
```
- Fetch an [input-addressed store path](@docroot@/glossary.md#gloss-input-addressed-store-object) as is. This depends on user configuration, which is less preferable.
Example:
```nix
builtins.fetchClosure {
fromStore = "https://cache.nixos.org";
fromPath = /nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1;
inputAddressed = true;
}
```
**Rewriting a store path**
This first example fetches `/nix/store/r2jd...` from the specified binary cache,
This example fetches `/nix/store/r2jd...` from the specified binary cache,
and rewrites it into the content-addressed store path
`/nix/store/ldbh...`.
By rewriting the store paths, you can add the contents to any store without requiring that you or perhaps your users configure any extra trust.
Like the previous example, no extra configuration or privileges are required.
To find out the correct value for `toPath` given a `fromPath`,
use [`nix store make-content-addressed`](@docroot@/command-ref/new-cli/nix3-store-make-content-addressed.md):
@ -268,20 +258,25 @@ static RegisterPrimOp primop_fetchClosure({
Alternatively, set `toPath = ""` and find the correct `toPath` in the error message.
**Not rewriting**
**Fetch an input-addressed store path as is**
`toPath` may be omitted when either
- `fromPath` is already content-addressed, or
- `inputAddressed = true;` is set.
Example:
Fetching an [input addressed path](@docroot@/glossary.md#gloss-input-addressed-store-object) is not recommended because it requires that the source be trusted by the Nix configuration.
```nix
builtins.fetchClosure {
fromStore = "https://cache.nixos.org";
fromPath = /nix/store/r2jd6ygnmirm2g803mksqqjm4y39yi6i-git-2.33.1;
inputAddressed = true;
}
```
It is possible to fetch an [input-addressed store path](@docroot@/glossary.md#gloss-input-addressed-store-object) and return it as is.
However, this is the least preferred way of invoking `fetchClosure`, because it requires that the input-addressed paths are trusted by the Nix configuration.
**`builtins.storePath`**
This function is similar to [`builtins.storePath`](#builtins-storePath) in that it
allows you to use a previously built store path in a Nix
expression. However, it is more reproducible because it requires
specifying a binary cache from which the path can be fetched.
`fetchClosure` is similar to [`builtins.storePath`](#builtins-storePath) in that it allows you to use a previously built store path in a Nix expression.
However, `fetchClosure` is more reproducible because it specifies a binary cache from which the path can be fetched.
Also, using content-addressed store paths does not require users to configure [`trusted-public-keys`](@docroot@/command-ref/conf-file.md#conf-trusted-public-keys) to ensure their authenticity.
)",
.fun = prim_fetchClosure,