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tracking issue: remove Value& out parameters #1136

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opened 2026-02-23 22:52:55 +00:00 by pennae · 5 comments
pennae commented 2026-02-23 22:52:55 +00:00
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main has pretty resonable support for returning values directly since pointer tagging happened. we should remove out parameters from all signatures and return proper values instead.

and numerous others probably

`main` has pretty resonable support for returning values directly since pointer tagging happened. we should remove out parameters from all signatures and return proper values instead. - [x] Expr::eval (https://gerrit.lix.systems/c/lix/+/5219) - [x] primops (https://gerrit.lix.systems/c/lix/+/5456) - [x] EvalState::callFunction (https://gerrit.lix.systems/c/lix/+/5253) - [x] EvalState::autoCallFunction (https://gerrit.lix.systems/c/lix/+/5291) - [x] EvalState::concatLists (https://gerrit.lix.systems/c/lix/+/5450) - [x] EvalState::eval\* (https://gerrit.lix.systems/c/lix/+/5254) - [x] EvalState::mk\* (https://gerrit.lix.systems/c/lix/+/5305, https://gerrit.lix.systems/c/lix/+/5303, others) - [x] Evaluator::evalLazily (https://gerrit.lix.systems/c/lix/+/5292) - [x] ~~getDerivation~~ - [x] parseJSON (https://gerrit.lix.systems/c/lix/+/5448) and numerous others probably
lix-bot commented 2026-02-23 23:07:22 +00:00
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This issue was mentioned on Gerrit on the following CLs:

  • comment in cl/5219 ("libexpr: migrate Expr::eval to return a Value, take 2")
  • commit message in cl/5305 ("libexpr: Migrate EvalState::mkOutputString to return a Value")
  • commit message in cl/5307 ("libexpr/primops/fromTOML: Migrate visit lambda to return a value")
  • commit message in cl/5303 ("libexpr: Migrate mkStorePathString to return a Value")
  • commit message in cl/5301 ("libexpr: Migrate makePositionThunks to return Value tuple")
  • commit message in cl/5308 ("libexpr: Migrate EvalState::mkPos to return a Value")
  • commit message in cl/5309 ("libexpr: Migrate emitTreeAttrs to return a Value")
  • commit message in cl/5446 ("libexpr: Migrate EvalPaths::allowAndSetStorePathString to return a Value")
  • commit message in cl/5453 ("libexpr/primops: Migrate helper fn fetch to return a Value")
  • commit message in cl/5452 ("libexpr/primops: Migrate helper fn fetchTree to return a Value")
  • commit message in cl/5451 ("libexpr/primops: Migrate helper fn anyorall to return a Value")
  • commit message in cl/5450 ("libexpr: Migrate EvalState::concatLists to return a Value")
  • commit message in cl/5449 ("libexpr/primops: Migrate helper fn elemAt to return a Value")
  • commit message in cl/5448 ("libexpr/json-to-value: Migrate parseJSON to return a Value")
  • commit message in cl/5447 ("lixexpr/primops: Migrate import helper fn to return a Value")
  • commit message in cl/5456 ("libexpr/primops: Migrate primops to return Values")
  • commit message in cl/5455 ("libexpr/primops: Migrate addPath to return a Value")
  • commit message in cl/5454 ("libexpr/primops: Migrate derivationStrictInternal to return a Value")
  • commit message in cl/5472 ("libexpr: Delete EvalState::mkSingleDerivedPathString dead function with Value& out param")
<!-- GERRIT_LINKBOT: {"cls": [{"backlink": "https://gerrit.lix.systems/c/lix/+/5219", "number": 5219, "kind": "comment"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5305", "number": 5305, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5307", "number": 5307, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5303", "number": 5303, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5301", "number": 5301, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5308", "number": 5308, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5309", "number": 5309, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5446", "number": 5446, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5453", "number": 5453, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5452", "number": 5452, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5451", "number": 5451, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5450", "number": 5450, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5449", "number": 5449, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5448", "number": 5448, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5447", "number": 5447, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5456", "number": 5456, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5455", "number": 5455, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5454", "number": 5454, "kind": "commit message"}, {"backlink": "https://gerrit.lix.systems/c/lix/+/5472", "number": 5472, "kind": "commit message"}], "cl_meta": {"5219": {"change_title": "libexpr: migrate Expr::eval to return a Value, take 2"}, "5305": {"change_title": "libexpr: Migrate EvalState::mkOutputString to return a Value"}, "5307": {"change_title": "libexpr/primops/fromTOML: Migrate `visit` lambda to return a value"}, "5303": {"change_title": "libexpr: Migrate mkStorePathString to return a Value"}, "5301": {"change_title": "libexpr: Migrate makePositionThunks to return Value tuple"}, "5308": {"change_title": "libexpr: Migrate EvalState::mkPos to return a Value"}, "5309": {"change_title": "libexpr: Migrate emitTreeAttrs to return a Value"}, "5446": {"change_title": "libexpr: Migrate EvalPaths::allowAndSetStorePathString to return a Value"}, "5453": {"change_title": "libexpr/primops: Migrate helper fn fetch to return a Value"}, "5452": {"change_title": "libexpr/primops: Migrate helper fn fetchTree to return a Value"}, "5451": {"change_title": "libexpr/primops: Migrate helper fn anyorall to return a Value"}, "5450": {"change_title": "libexpr: Migrate EvalState::concatLists to return a Value"}, "5449": {"change_title": "libexpr/primops: Migrate helper fn elemAt to return a Value"}, "5448": {"change_title": "libexpr/json-to-value: Migrate parseJSON to return a Value"}, "5447": {"change_title": "lixexpr/primops: Migrate import helper fn to return a Value"}, "5456": {"change_title": "libexpr/primops: Migrate primops to return Values"}, "5455": {"change_title": "libexpr/primops: Migrate addPath to return a Value"}, "5454": {"change_title": "libexpr/primops: Migrate derivationStrictInternal to return a Value"}, "5472": {"change_title": "libexpr: Delete EvalState::mkSingleDerivedPathString dead function with Value& out param"}}} --> This issue was mentioned on Gerrit on the following CLs: * comment in [cl/5219](https://gerrit.lix.systems/c/lix/+/5219) ("libexpr: migrate Expr::eval to return a Value, take 2") * commit message in [cl/5305](https://gerrit.lix.systems/c/lix/+/5305) ("libexpr: Migrate EvalState::mkOutputString to return a Value") * commit message in [cl/5307](https://gerrit.lix.systems/c/lix/+/5307) ("libexpr/primops/fromTOML: Migrate `visit` lambda to return a value") * commit message in [cl/5303](https://gerrit.lix.systems/c/lix/+/5303) ("libexpr: Migrate mkStorePathString to return a Value") * commit message in [cl/5301](https://gerrit.lix.systems/c/lix/+/5301) ("libexpr: Migrate makePositionThunks to return Value tuple") * commit message in [cl/5308](https://gerrit.lix.systems/c/lix/+/5308) ("libexpr: Migrate EvalState::mkPos to return a Value") * commit message in [cl/5309](https://gerrit.lix.systems/c/lix/+/5309) ("libexpr: Migrate emitTreeAttrs to return a Value") * commit message in [cl/5446](https://gerrit.lix.systems/c/lix/+/5446) ("libexpr: Migrate EvalPaths::allowAndSetStorePathString to return a Value") * commit message in [cl/5453](https://gerrit.lix.systems/c/lix/+/5453) ("libexpr/primops: Migrate helper fn fetch to return a Value") * commit message in [cl/5452](https://gerrit.lix.systems/c/lix/+/5452) ("libexpr/primops: Migrate helper fn fetchTree to return a Value") * commit message in [cl/5451](https://gerrit.lix.systems/c/lix/+/5451) ("libexpr/primops: Migrate helper fn anyorall to return a Value") * commit message in [cl/5450](https://gerrit.lix.systems/c/lix/+/5450) ("libexpr: Migrate EvalState::concatLists to return a Value") * commit message in [cl/5449](https://gerrit.lix.systems/c/lix/+/5449) ("libexpr/primops: Migrate helper fn elemAt to return a Value") * commit message in [cl/5448](https://gerrit.lix.systems/c/lix/+/5448) ("libexpr/json-to-value: Migrate parseJSON to return a Value") * commit message in [cl/5447](https://gerrit.lix.systems/c/lix/+/5447) ("lixexpr/primops: Migrate import helper fn to return a Value") * commit message in [cl/5456](https://gerrit.lix.systems/c/lix/+/5456) ("libexpr/primops: Migrate primops to return Values") * commit message in [cl/5455](https://gerrit.lix.systems/c/lix/+/5455) ("libexpr/primops: Migrate addPath to return a Value") * commit message in [cl/5454](https://gerrit.lix.systems/c/lix/+/5454) ("libexpr/primops: Migrate derivationStrictInternal to return a Value") * commit message in [cl/5472](https://gerrit.lix.systems/c/lix/+/5472) ("libexpr: Delete EvalState::mkSingleDerivedPathString dead function with Value& out param")
sky1e self-assigned this 2026-04-10 20:48:48 +00:00
ifreilicht commented 2026-04-16 09:43:26 +00:00
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@sky1e Are you still working on this? I have a potential solution for getDerivation and potentially others but don't want to steal your fire if you want to get this over the finish line.

@sky1e Are you still working on this? I have a potential solution for `getDerivation` and potentially others but don't want to steal your fire if you want to get this over the finish line.
sky1e commented 2026-04-16 14:20:49 +00:00
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@ifreilicht wrote in #1136 (comment):

@sky1e Are you still working on this? I have a potential solution for getDerivation and potentially others but don't want to steal your fire if you want to get this over the finish line.

Maybe I'm missing something, but I don't see any Value& out params in any of the getDerivation(s) functions.

https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L405-L410
This one forces v, so it's using the provided value.

https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L428-L435
This one calls the above with its v parameter.

https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L449-L454
This one evaluates its vIn as a function.

https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L555-560
And this one calls the previous with its v.

@ifreilicht wrote in https://git.lix.systems/lix-project/lix/issues/1136#issuecomment-18520: > @sky1e Are you still working on this? I have a potential solution for `getDerivation` and potentially others but don't want to steal your fire if you want to get this over the finish line. Maybe I'm missing something, but I don't see any `Value&` out params in any of the `getDerivation(s)` functions. https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L405-L410 This one forces `v`, so it's using the provided value. https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L428-L435 This one calls the above with its `v` parameter. https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L449-L454 This one evaluates its `vIn` as a function. https://git.lix.systems/lix-project/lix/src/branch/main/lix/libexpr/get-drvs.cc#L555-560 And this one calls the previous with its `v`.
sky1e commented 2026-04-16 14:33:14 +00:00
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I believe with https://gerrit.lix.systems/c/lix/+/5472 that will be all Value& out parameters removed, though I wouldn't mind a second pair of eyes to check if I missed anything.

I believe with https://gerrit.lix.systems/c/lix/+/5472 that will be all `Value&` out parameters removed, though I wouldn't mind a second pair of eyes to check if I missed anything.
ifreilicht commented 2026-04-16 15:14:42 +00:00
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Ah you're right, I didn't understand what forceValue does, I'm still kinda new to the evaluator. That function does still has an out-param in DrvInfos & drvs, but not sure if that's something we also want to fix.

I believe with https://gerrit.lix.systems/c/lix/+/5472 that will be all Value& out parameters removed, though I wouldn't mind a second pair of eyes to check if I missed anything.

That's the only other one I found as well. Wasn't sure if it could be removed. I believe I remember that libexpr was supposed to have a public interface at some point and maybe that's part of it?

Ah you're right, I didn't understand what `forceValue` does, I'm still kinda new to the evaluator. That function does still has an out-param in `DrvInfos & drvs`, but not sure if that's something we also want to fix. > I believe with https://gerrit.lix.systems/c/lix/+/5472 that will be all `Value&` out parameters removed, though I wouldn't mind a second pair of eyes to check if I missed anything. That's the only other one I found as well. Wasn't sure if it could be removed. I believe I remember that `libexpr` was supposed to have a public interface at some point and maybe that's part of it?
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