Revert "Revert "Revert "Adapt scheduler to work with dynamic derivations"""

The bug reappeared after all, and the fix introduced a different bug. I
just reverted on 2.27 first, in #12576, but upon further introspection
and discussion with @roberth, with preparing for and travelling to
Planet Nix I will not be able to fix it on `master` soon enough for a
revert to not be warranted here in the meantime also.

This reverts commit c985252.

Author: Ericson2314

src/libstore/build/derivation-creation-and-realisation-goal.cc

@@ -137,8 +137,21 @@ Goal::Co DerivationGoal::init() {
     trace("init");
 
     if (useDerivation) {
+        /* The first thing to do is to make sure that the derivation
+           exists.  If it doesn't, it may be created through a
+           substitute. */
+
+        if (buildMode != bmNormal || !worker.evalStore.isValidPath(drvPath)) {
+            addWaitee(upcast_goal(worker.makePathSubstitutionGoal(drvPath)));
+            co_await Suspend{};
+        }
+
         trace("loading derivation");
 
+        if (nrFailed != 0) {
+            co_return done(BuildResult::MiscFailure, {}, Error("cannot build missing derivation '%s'", worker.store.printStorePath(drvPath)));
+        }
+
         /* `drvPath' should already be a root, but let's be on the safe
            side: if the user forgot to make it a root, we wouldn't want
            things being garbage collected while we're busy. */
@@ -1540,24 +1553,23 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
     if (!useDerivation || !drv) return;
     auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
 
-    std::optional info = tryGetConcreteDrvGoal(waitee);
-    if (!info) return;
-    const auto & [dg, drvReq] = *info;
+    auto * dg = dynamic_cast<DerivationGoal *>(&*waitee);
+    if (!dg) return;
 
-    auto * nodeP = fullDrv.inputDrvs.findSlot(drvReq.get());
+    auto * nodeP = fullDrv.inputDrvs.findSlot(DerivedPath::Opaque { .path = dg->drvPath });
     if (!nodeP) return;
     auto & outputs = nodeP->value;
 
     for (auto & outputName : outputs) {
-        auto buildResult = dg.get().getBuildResult(DerivedPath::Built {
-            .drvPath = makeConstantStorePathRef(dg.get().drvPath),
+        auto buildResult = dg->getBuildResult(DerivedPath::Built {
+            .drvPath = makeConstantStorePathRef(dg->drvPath),
             .outputs = OutputsSpec::Names { outputName },
         });
         if (buildResult.success()) {
             auto i = buildResult.builtOutputs.find(outputName);
             if (i != buildResult.builtOutputs.end())
                 inputDrvOutputs.insert_or_assign(
-                    { dg.get().drvPath, outputName },
+                    { dg->drvPath, outputName },
                     i->second.outPath);
         }
     }

src/libstore/build/derivation-creation-and-realisation-goal.hh

@@ -57,10 +57,6 @@ struct InitialOutput {
 
 /**
  * A goal for building some or all of the outputs of a derivation.
- *
- * The derivation must already be present, either in the store in a drv
- * or in memory. If the derivation itself needs to be gotten first, a
- * `DerivationCreationAndRealisationGoal` goal must be used instead.
  */
 struct DerivationGoal : public Goal
 {

src/libstore/build/derivation-goal.cc

@@ -1,7 +1,6 @@
 #include "worker.hh"
 #include "substitution-goal.hh"
 #ifndef _WIN32 // TODO Enable building on Windows
-#  include "derivation-creation-and-realisation-goal.hh"
 #  include "derivation-goal.hh"
 #endif
 #include "local-store.hh"
@@ -30,8 +29,8 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
         }
         if (i->exitCode != Goal::ecSuccess) {
 #ifndef _WIN32 // TODO Enable building on Windows
-            if (auto i2 = dynamic_cast<DerivationCreationAndRealisationGoal *>(i.get()))
-                failed.insert(i2->drvReq->to_string(*this));
+            if (auto i2 = dynamic_cast<DerivationGoal *>(i.get()))
+                failed.insert(printStorePath(i2->drvPath));
             else
 #endif
             if (auto i2 = dynamic_cast<PathSubstitutionGoal *>(i.get()))

src/libstore/build/derivation-goal.hh

@@ -175,7 +175,7 @@ Goal::Done Goal::amDone(ExitCode result, std::optional<Error> ex)
     exitCode = result;
 
     if (ex) {
-        if (!preserveException && !waiters.empty())
+        if (!waiters.empty())
             logError(ex->info());
         else
             this->ex = std::move(*ex);

src/libstore/build/entry-points.cc

@@ -50,16 +50,6 @@ enum struct JobCategory {
      * A substitution an arbitrary store object; it will use network resources.
      */
     Substitution,
-    /**
-     * A goal that does no "real" work by itself, and just exists to depend on
-     * other goals which *do* do real work. These goals therefore are not
-     * limited.
-     *
-     * These goals cannot infinitely create themselves, so there is no risk of
-     * a "fork bomb" type situation (which would be a problem even though the
-     * goal do no real work) either.
-     */
-    Administration,
 };
 
 struct Goal : public std::enable_shared_from_this<Goal>
@@ -383,17 +373,6 @@ public:
      */
     BuildResult getBuildResult(const DerivedPath &) const;
 
-    /**
-     * Hack to say that this goal should not log `ex`, but instead keep
-     * it around. Set by a waitee which sees itself as the designated
-     * continuation of this goal, responsible for reporting its
-     * successes or failures.
-     *
-     * @todo this is yet another not-nice hack in the goal system that
-     * we ought to get rid of. See #11927
-     */
-    bool preserveException = false;
-
     /**
      * Exception containing an error message, if any.
      */