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Make the Derived Path family of types inductive for dynamic derivations

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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>
This commit is contained in:
John Ericson 2023-01-15 17:39:04 -05:00
parent d00fe5f225
commit 60b7121d2c
48 changed files with 1136 additions and 267 deletions
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7
src/libexpr/primops/context.cc
View file

@ -106,7 +106,10 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
contextInfos[std::move(d.drvPath)].allOutputs = true;
},
[&](NixStringContextElem::Built && b) {
contextInfos[std::move(b.drvPath)].outputs.emplace_back(std::move(b.output));
// FIXME should eventually show string context as is, no
// resolving here.
auto drvPath = resolveDerivedPath(*state.store, *b.drvPath);
contextInfos[std::move(drvPath)].outputs.emplace_back(std::move(b.output));
},
[&](NixStringContextElem::Opaque && o) {
contextInfos[std::move(o.path)].path = true;
@ -222,7 +225,7 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
for (auto elem : iter->value->listItems()) {
auto outputName = state.forceStringNoCtx(*elem, iter->pos, "while evaluating an output name within a string context");
context.emplace(NixStringContextElem::Built {
.drvPath = namePath,
.drvPath = makeConstantStorePathRef(namePath),
.output = std::string { outputName },
});
}