32 lines
1.2 KiB
Markdown
32 lines
1.2 KiB
Markdown
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## `invalidateFetcherByDrvHash` {#sec-pkgs-invalidateFetcherByDrvHash}
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Use the derivation hash to invalidate the output via name, for testing.
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Type: `(a@{ name, ... } -> Derivation) -> a -> Derivation`
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Normally, fixed output derivations can and should be cached by their output
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hash only, but for testing we want to re-fetch everytime the fetcher changes.
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Changes to the fetcher become apparent in the drvPath, which is a hash of
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how to fetch, rather than a fixed store path.
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By inserting this hash into the name, we can make sure to re-run the fetcher
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every time the fetcher changes.
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This relies on the assumption that Nix isn't clever enough to reuse its
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database of local store contents to optimize fetching.
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You might notice that the "salted" name derives from the normal invocation,
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not the final derivation. `invalidateFetcherByDrvHash` has to invoke the fetcher
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function twice: once to get a derivation hash, and again to produce the final
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fixed output derivation.
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Example:
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tests.fetchgit = invalidateFetcherByDrvHash fetchgit {
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name = "nix-source";
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url = "https://github.com/NixOS/nix";
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rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
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sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
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};
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