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Make KeyedBuildResult, BuildResult like before, and fix bug another way

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In https://github.com/NixOS/nix/pull/6311#discussion_r834863823, I
realized since derivation goals' wanted outputs can "grow" due to
overlapping dependencies (See `DerivationGoal::addWantedOutputs`, called
by `Worker::makeDerivationGoalCommon`), the previous bug fix had an
unfortunate side effect of causing more pointless rebuilds.

In paticular, we have this situation:

1. Goal made from `DerivedPath::Built { foo, {a} }`.

2. Goal gives on on substituting, starts building.

3. Goal made from `DerivedPath::Built { foo, {b} }`, in fact is just
   modified original goal.

4. Though the goal had gotten as far as building, so all outputs were
   going to be produced, `addWantedOutputs` no longer knows that and so
   the goal is flagged to be restarted.

This might sound far-fetched with input-addressed drvs, where we usually
basically have all our goals "planned out" before we start doing
anything, but with CA derivation goals and especially RFC 92, where *drv
resolution* means goals are created after some building is completed, it
is more likely to happen.

So the first thing to do was restore the clearing of `wantedOutputs` we
used to do, and then filter the outputs in `buildPathsWithResults` to
only get the ones we care about.

But fix also has its own side effect in that the `DerivedPath` in the
`BuildResult` in `DerivationGoal` cannot be trusted; it is merely the
*first* `DerivedPath` for which this goal was originally created.

To remedy this, I made `BuildResult` be like it was before, and instead
made `KeyedBuildResult` be a subclass wit the path. Only
`buildPathsWithResults` returns `KeyedBuildResult`s, everything else
just becomes like it was before, where the "key" is unambiguous from
context.

I think separating the "primary key" field(s) from the other fields is
good practical in general anyways. (I would like to do the same thing
for `ValidPathInfo`.) Among other things, it allows constructions like
`std::map<Key, ThingWithKey>` where doesn't contain duplicate keys and
just precludes the possibility of those duplicate keys being out of
sync.

We might leverage the above someday to overload `buildPathsWithResults`
to take a *set* of return a *map* per the above.

-----

Unfortunately, we need to avoid C++20 strictness on designated
initializers.

(BTW
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2287r1.html
this offers some new syntax for this use-case. Hopefully this will be
adopted and we can eventually use it.)

No having that yet, maybe it would be better to not make
`KeyedBuildResult` a subclass to just avoid this.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
This commit is contained in:
John Ericson 2022-03-25 01:26:07 +00:00
parent 9df7f3f537
commit 37fca662b0
11 changed files with 130 additions and 51 deletions
Download patch file Download diff file Expand all files Collapse all files

30
src/libstore/build/derivation-goal.cc
View file

@ -330,6 +330,10 @@ void DerivationGoal::outputsSubstitutionTried()
produced using a substitute. So we have to build instead. */
void DerivationGoal::gaveUpOnSubstitution()
{
/* Make sure checkPathValidity() from now on checks all
outputs. */
wantedOutputs = OutputsSpec::All { };
/* The inputs must be built before we can build this goal. */
inputDrvOutputs.clear();
if (useDerivation)
@ -570,8 +574,6 @@ void DerivationGoal::inputsRealised()
build hook. */
state = &DerivationGoal::tryToBuild;
worker.wakeUp(shared_from_this());
buildResult = BuildResult { .path = buildResult.path };
}
void DerivationGoal::started()
@ -1452,12 +1454,28 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
{
Goal::waiteeDone(waitee, result);
if (waitee->buildResult.success())
if (auto bfd = std::get_if<DerivedPath::Built>(&waitee->buildResult.path))
for (auto & [output, realisation] : waitee->buildResult.builtOutputs)
if (!useDerivation) return;
auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
auto * dg = dynamic_cast<DerivationGoal *>(&*waitee);
if (!dg) return;
auto outputs = fullDrv.inputDrvs.find(dg->drvPath);
if (outputs == fullDrv.inputDrvs.end()) return;
for (auto & outputName : outputs->second) {
auto buildResult = dg->getBuildResult(DerivedPath::Built {
.drvPath = dg->drvPath,
.outputs = OutputsSpec::Names { outputName },
});
if (buildResult.success()) {
for (auto & [output, realisation] : buildResult.builtOutputs) {
inputDrvOutputs.insert_or_assign(
{ bfd->drvPath, output.outputName },
{ dg->drvPath, output.outputName },
realisation.outPath);
}
}
}
}
}