Make buildPathsWithResults() only return info on wanted outputs #6311
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This avoids an infinite loop in the final test in tests/binary-cache.sh. I think this was only not triggered previously by accident (because we were clearing wantedOutputs in between).
edolstra
commented
Mar 24, 2022
| /* At least one of the output paths could not be | ||
| produced using a substitute. So we have to build instead. */ | ||
| void DerivationGoal::gaveUpOnSubstitution() | ||
| { | ||
| /* Make sure checkPathValidity() from now on checks all | ||
| outputs. */ | ||
| wantedOutputs.clear(); |
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I couldn't see any reason why checkPathValidity() needs to check all outputs. In any case, messing with wantedOutputs seems dirty...
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I agree it is dirty, but the idea I think (I did not write that but remember reading it IIRC) that since we are now doing the build, we will be making all afresh outputs, and we should fail if the derivation did not produce all the outputs even if we already had the missing outputs before.
Without this, we run the risk of some wonky non-deterministic derivation that produces a different subset of the outputs each time not failing as it should.
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Oh, another reason is that if during a build we discover we in fact need other outputs, it is nice to know we don't need to restart a build that got so upgraded. See DerivationGoal::addWantedOutputs
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A consequence of this is that I think buildPathsWithResults is going to need to filter the results based on the derived path. I will make a PR removing the derived path from the build result stored by the derivation goal, because I no longer think it is correct.
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From what I can tell, what outputs get build/registered (or whose absence causes the build to fail) is unaffected by wantedOutputs or initialOutputs.*.wanted. So I think it should be okay. Restarts are only needed in the substitution case, not when we're actually building.
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@edolstra On what basis do you think this?
See Worker::makeDerivationGoalCommon. If a new goal needs to be created that overlaps with an existing goal, this function is called. This may occur at any point over the derivation goal's lifecycle.
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I will fix this in the other PR too, sigh.
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Think what? I'm not sure I understand the problem...
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See the long PR description in #6312
Ericson2314
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Mar 25, 2022
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In NixOS#6311 (comment), I realized since derivation goals' wanted outputs can "grow" due to overlapping dependencies (See `DerivationGoal::addWantedOutputs`), 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 to someday overload `buildPathsWithResults` to take a *set* of return a *map* per the above.
Ericson2314
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In NixOS#6311 (comment), I realized since derivation goals' wanted outputs can "grow" due to overlapping dependencies (See `DerivationGoal::addWantedOutputs`), 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 to someday overload `buildPathsWithResults` to take a *set* of return a *map* per the above.
Ericson2314
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In NixOS#6311 (comment), I realized since derivation goals' wanted outputs can "grow" due to overlapping dependencies (See `DerivationGoal::addWantedOutputs`), 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.
Merged
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Co-authored-by: John Ericson <git@JohnEricson.me>
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…er way In NixOS#6311 (comment), 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 content addressed 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.
Ericson2314
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Mar 25, 2022
…er way In NixOS#6311 (comment), 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.
Merged
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: https://discourse.nixos.org/t/tweag-nix-dev-update-27/18433/1 |
This was referenced Apr 25, 2022
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Ericson2314
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…er way In NixOS#6311 (comment), 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.
Ericson2314
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…er way In NixOS#6311 (comment), 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>
Ericson2314
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…er way In NixOS#6311 (comment), 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>
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This fixes a regression in
nix build(mentioned here) where it would print all outputs when building, but only the wanted outputs otherwise. Now it only prints the wanted outputs, as before.It also fixes a potential infinite loop when retrying substitutions after an incomplete closure.