Update doc/builders/fetchers.chapter.md

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
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Cody Hiar 2022-08-02 10:52:08 -06:00 committed by GitHub
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@ -5,7 +5,11 @@ Building software with Nix often requires downloading source code and other file
## Caveats
Fetchers create [_fixed output derivations_](https://nixos.org/manual/nix/stable/#fixed-output-drvs) that downloaded files. Later, Nix can reuse the downloaded files via their hash. While the caching improves performance, it can lead to some confusion. For example, consider the following fetcher:
Fetchers create [fixed output derivations](https://nixos.org/manual/nix/stable/#fixed-output-drvs) from downloaded files.
Nix can reuse the downloaded files via the hash of the resulting derivation.
The fact that the hash belongs to the Nix derivation output and not the file itself can lead to confusion.
For example, consider the following fetcher:
```nix
fetchurl {