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Progress on #13405, which asks for an explicit characterisation of the equivalence relation like the one given here. Also progress on #11895, because we're using the term "build trace entry" instead of "realisation". Mention #9259, a future work item. Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
40 lines
1.6 KiB
Markdown
40 lines
1.6 KiB
Markdown
# Derivation "ATerm" file format
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For historical reasons, [store derivations][store derivation] are stored on-disk in "Annotated Term" (ATerm) format
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([guide](https://homepages.cwi.nl/~daybuild/daily-books/technology/aterm-guide/aterm-guide.html),
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[paper](https://doi.org/10.1002/(SICI)1097-024X(200003)30:3%3C259::AID-SPE298%3E3.0.CO;2-Y)).
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## The ATerm format used
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Derivations are serialised in one of the following formats:
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- ```
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Derive(...)
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```
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For all stable derivations.
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- ```
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DrvWithVersion(<version-string>, ...)
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```
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The only `version-string`s that are in use today are for [experimental features](@docroot@/development/experimental-features.md):
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- `"xp-dyn-drv"` for the [`dynamic-derivations`](@docroot@/development/experimental-features.md#xp-feature-dynamic-derivations) experimental feature.
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## Use for encoding to store object
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When derivation is encoded to a [store object] we make the following choices:
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- The store path name is the derivation name with `.drv` suffixed at the end
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Indeed, the ATerm format above does *not* contain the name of the derivation, on the assumption that a store path will also be provided out-of-band.
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- The derivation is content-addressed using the ["Text" method] of content-addressing derivations
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Currently we always encode derivations to store object using the ATerm format (and the previous two choices),
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but we reserve the option to encode new sorts of derivations differently in the future.
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[store derivation]: @docroot@/glossary.md#gloss-store-derivation
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[store object]: @docroot@/glossary.md#gloss-store-object
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["Text" method]: @docroot@/store/store-object/content-address.md#method-text
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