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Lazily copy trees to the store

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We now mount lazy accessors on top of /nix/store without materializing
them, and only materialize them to the real store if needed (e.g. in
the `derivation` primop).
This commit is contained in:
Eelco Dolstra 2025-04-08 23:32:52 +02:00
parent c891554999
commit febd28db87
14 changed files with 122 additions and 50 deletions
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13
src/libexpr/primops.cc
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@ -14,6 +14,7 @@
#include "nix/expr/value-to-xml.hh"
#include "nix/expr/primops.hh"
#include "nix/fetchers/fetch-to-store.hh"
#include "nix/util/mounted-source-accessor.hh"
#include <boost/container/small_vector.hpp>
#include <nlohmann/json.hpp>
@ -75,7 +76,10 @@ StringMap EvalState::realiseContext(const NixStringContext & context, StorePathS
ensureValid(b.drvPath->getBaseStorePath());
},
[&](const NixStringContextElem::Opaque & o) {
ensureValid(o.path);
// We consider virtual store paths valid here. They'll
// be devirtualized if needed elsewhere.
if (!storeFS->getMount(CanonPath(store->printStorePath(o.path))))
ensureValid(o.path);
if (maybePathsOut)
maybePathsOut->emplace(o.path);
},
@ -1408,6 +1412,8 @@ static void derivationStrictInternal(
/* Everything in the context of the strings in the derivation
attributes should be added as dependencies of the resulting
derivation. */
StringMap rewrites;
for (auto & c : context) {
std::visit(overloaded {
/* Since this allows the builder to gain access to every
@ -1430,11 +1436,13 @@ static void derivationStrictInternal(
drv.inputDrvs.ensureSlot(*b.drvPath).value.insert(b.output);
},
[&](const NixStringContextElem::Opaque & o) {
drv.inputSrcs.insert(o.path);
drv.inputSrcs.insert(state.devirtualize(o.path, &rewrites));
},
}, c.raw);
}
drv.applyRewrites(rewrites);
/* Do we have all required attributes? */
if (drv.builder == "")
state.error<EvalError>("required attribute 'builder' missing")
@ -2500,6 +2508,7 @@ static void addPath(
{}));
if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
// FIXME: make this lazy?
auto dstPath = fetchToStore(
*state.store,
path.resolveSymlinks(),