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60b7121d2c
We want to be able to write down `foo.drv^bar.drv^baz`:
`foo.drv^bar.drv` is the dynamic derivation (since it is itself a
derivation output, `bar.drv` from `foo.drv`).
To that end, we create `Single{Derivation,BuiltPath}` types, that are
very similar except instead of having multiple outputs (in a set or
map), they have a single one. This is for everything to the left of the
rightmost `^`.
`NixStringContextElem` has an analogous change, and now can reuse
`SingleDerivedPath` at the top level. In fact, if we ever get rid of
`DrvDeep`, `NixStringContextElem` could be replaced with
`SingleDerivedPath` entirely!
Important note: some JSON formats have changed.
We already can *produce* dynamic derivations, but we can't refer to them
directly. Today, we can merely express building or example at the top
imperatively over time by building `foo.drv^bar.drv`, and then with a
second nix invocation doing `<result-from-first>^baz`, but this is not
declarative. The ethos of Nix of being able to write down the full plan
everything you want to do, and then execute than plan with a single
command, and for that we need the new inductive form of these types.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
91 lines
3 KiB
C++
91 lines
3 KiB
C++
#pragma once
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///@file
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#include "hash.hh"
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#include "path.hh"
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#include "derived-path.hh"
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namespace nix {
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/**
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* Downstream Placeholders are opaque and almost certainly unique values
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* used to allow derivations to refer to store objects which are yet to
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* be built and for we do not yet have store paths for.
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*
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* They correspond to `DerivedPaths` that are not `DerivedPath::Opaque`,
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* except for the cases involving input addressing or fixed outputs
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* where we do know a store path for the derivation output in advance.
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*
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* Unlike `DerivationPath`, however, `DownstreamPlaceholder` is
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* purposefully opaque and obfuscated. This is so they are hard to
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* create by accident, and so substituting them (once we know what the
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* path to store object is) is unlikely to capture other stuff it
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* shouldn't.
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*
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* We use them with `Derivation`: the `render()` method is called to
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* render an opaque string which can be used in the derivation, and the
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* resolving logic can substitute those strings for store paths when
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* resolving `Derivation.inputDrvs` to `BasicDerivation.inputSrcs`.
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*/
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class DownstreamPlaceholder
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{
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/**
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* `DownstreamPlaceholder` is just a newtype of `Hash`.
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* This its only field.
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*/
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Hash hash;
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/**
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* Newtype constructor
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*/
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DownstreamPlaceholder(Hash hash) : hash(hash) { }
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public:
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/**
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* This creates an opaque and almost certainly unique string
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* deterministically from the placeholder.
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*/
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std::string render() const;
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/**
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* Create a placeholder for an unknown output of a content-addressed
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* derivation.
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*
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* The derivation itself is known (we have a store path for it), but
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* the output doesn't yet have a known store path.
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*
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* @param xpSettings Stop-gap to avoid globals during unit tests.
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*/
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static DownstreamPlaceholder unknownCaOutput(
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const StorePath & drvPath,
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std::string_view outputName,
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const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
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/**
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* Create a placehold for the output of an unknown derivation.
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*
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* The derivation is not yet known because it is a dynamic
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* derivaiton --- it is itself an output of another derivation ---
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* and we just have (another) placeholder for it.
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*
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* @param xpSettings Stop-gap to avoid globals during unit tests.
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*/
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static DownstreamPlaceholder unknownDerivation(
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const DownstreamPlaceholder & drvPlaceholder,
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std::string_view outputName,
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const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
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/**
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* Convenience constructor that handles both cases (unknown
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* content-addressed output and unknown derivation), delegating as
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* needed to `unknownCaOutput` and `unknownDerivation`.
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*
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* Recursively builds up a placeholder from a
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* `SingleDerivedPath::Built.drvPath` chain.
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*/
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static DownstreamPlaceholder fromSingleDerivedPathBuilt(
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const SingleDerivedPath::Built & built);
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};
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}
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