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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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50
src/libstore/remote-store.cc
View file

@ -125,10 +125,26 @@ void write(const Store & store, Sink & out, const DrvOutput & drvOutput)
}
BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
KeyedBuildResult read(const Store & store, Source & from, Phantom<KeyedBuildResult> _)
{
auto path = worker_proto::read(store, from, Phantom<DerivedPath> {});
BuildResult res { .path = path };
auto br = worker_proto::read(store, from, Phantom<BuildResult> {});
return KeyedBuildResult {
std::move(br),
/* .path = */ std::move(path),
};
}
void write(const Store & store, Sink & to, const KeyedBuildResult & res)
{
worker_proto::write(store, to, res.path);
worker_proto::write(store, to, static_cast<const BuildResult &>(res));
}
BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
{
BuildResult res;
res.status = (BuildResult::Status) readInt(from);
from
>> res.errorMsg
@ -142,7 +158,6 @@ BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
void write(const Store & store, Sink & to, const BuildResult & res)
{
worker_proto::write(store, to, res.path);
to
<< res.status
<< res.errorMsg
@ -865,7 +880,7 @@ void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMod
readInt(conn->from);
}
std::vector<BuildResult> RemoteStore::buildPathsWithResults(
std::vector<KeyedBuildResult> RemoteStore::buildPathsWithResults(
const std::vector<DerivedPath> & paths,
BuildMode buildMode,
std::shared_ptr<Store> evalStore)
@ -880,7 +895,7 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
writeDerivedPaths(*this, conn, paths);
conn->to << buildMode;
conn.processStderr();
return worker_proto::read(*this, conn->from, Phantom<std::vector<BuildResult>> {});
return worker_proto::read(*this, conn->from, Phantom<std::vector<KeyedBuildResult>> {});
} else {
// Avoid deadlock.
conn_.reset();
@ -889,21 +904,25 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
// fails, but meh.
buildPaths(paths, buildMode, evalStore);
std::vector<BuildResult> results;
std::vector<KeyedBuildResult> results;
for (auto & path : paths) {
std::visit(
overloaded {
[&](const DerivedPath::Opaque & bo) {
results.push_back(BuildResult {
.status = BuildResult::Substituted,
.path = bo,
results.push_back(KeyedBuildResult {
{
.status = BuildResult::Substituted,
},
/* .path = */ bo,
});
},
[&](const DerivedPath::Built & bfd) {
BuildResult res {
.status = BuildResult::Built,
.path = bfd,
KeyedBuildResult res {
{
.status = BuildResult::Built
},
/* .path = */ bfd,
};
OutputPathMap outputs;
@ -952,12 +971,7 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
writeDerivation(conn->to, *this, drv);
conn->to << buildMode;
conn.processStderr();
BuildResult res {
.path = DerivedPath::Built {
.drvPath = drvPath,
.outputs = OutputsSpec::All { },
},
};
BuildResult res;
res.status = (BuildResult::Status) readInt(conn->from);
conn->from >> res.errorMsg;
if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {