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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
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29
src/libstore/build/entry-points.cc
View file

@ -39,7 +39,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
}
}
std::vector<BuildResult> Store::buildPathsWithResults(
std::vector<KeyedBuildResult> Store::buildPathsWithResults(
const std::vector<DerivedPath> & reqs,
BuildMode buildMode,
std::shared_ptr<Store> evalStore)
@ -47,15 +47,23 @@ std::vector<BuildResult> Store::buildPathsWithResults(
Worker worker(*this, evalStore ? *evalStore : *this);
Goals goals;
for (const auto & br : reqs)
goals.insert(worker.makeGoal(br, buildMode));
std::vector<std::pair<const DerivedPath &, GoalPtr>> state;
for (const auto & req : reqs) {
auto goal = worker.makeGoal(req, buildMode);
goals.insert(goal);
state.push_back({req, goal});
}
worker.run(goals);
std::vector<BuildResult> results;
std::vector<KeyedBuildResult> results;
for (auto & i : goals)
results.push_back(i->buildResult);
for (auto & [req, goalPtr] : state)
results.emplace_back(KeyedBuildResult {
goalPtr->getBuildResult(req),
/* .path = */ req,
});
return results;
}
@ -68,15 +76,14 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
try {
worker.run(Goals{goal});
return goal->buildResult;
return goal->getBuildResult(DerivedPath::Built {
.drvPath = drvPath,
.outputs = OutputsSpec::All {},
});
} catch (Error & e) {
return BuildResult {
.status = BuildResult::MiscFailure,
.errorMsg = e.msg(),
.path = DerivedPath::Built {
.drvPath = drvPath,
.outputs = OutputsSpec::All { },
},
};
};
}