Make the Derived Path family of types inductive for dynamic derivations

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>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 5e37f7ecb..8bdf2f367 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -65,7 +65,7 @@ namespace nix {
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath,
     const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
+    : Goal(worker, DerivedPath::Built { .drvPath = makeConstantStorePathRef(drvPath), .outputs = wantedOutputs })
     , useDerivation(true)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)
@@ -74,7 +74,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath,
     state = &DerivationGoal::getDerivation;
     name = fmt(
         "building of '%s' from .drv file",
-        DerivedPath::Built { drvPath, wantedOutputs }.to_string(worker.store));
+        DerivedPath::Built { makeConstantStorePathRef(drvPath), wantedOutputs }.to_string(worker.store));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -84,7 +84,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath,
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
     const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
-    : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
+    : Goal(worker, DerivedPath::Built { .drvPath = makeConstantStorePathRef(drvPath), .outputs = wantedOutputs })
     , useDerivation(false)
     , drvPath(drvPath)
     , wantedOutputs(wantedOutputs)
@@ -95,7 +95,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation
     state = &DerivationGoal::haveDerivation;
     name = fmt(
         "building of '%s' from in-memory derivation",
-        DerivedPath::Built { drvPath, drv.outputNames() }.to_string(worker.store));
+        DerivedPath::Built { makeConstantStorePathRef(drvPath), drv.outputNames() }.to_string(worker.store));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -1490,7 +1490,7 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
 
     for (auto & outputName : outputs->second) {
         auto buildResult = dg->getBuildResult(DerivedPath::Built {
-            .drvPath = dg->drvPath,
+            .drvPath = makeConstantStorePathRef(dg->drvPath),
             .outputs = OutputsSpec::Names { outputName },
         });
         if (buildResult.success()) {