GCI: During reachability analysis don't try to evaluate the initializer of overly generic free const items#153269
GCI: During reachability analysis don't try to evaluate the initializer of overly generic free const items#153269fmease wants to merge 1 commit intorust-lang:mainfrom
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…er of overly generic free const items
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Going off on a tangent, the whole "don't eval the initializer for non-lifetime-parametric free const items" thing doesn't apply to mGCA's type-level consts which I'm pretty sure is very intentional (IINM) and thus fine, it's also not GCI-specific, e.g., trait T { type const K: usize = const { panic!(); }; } (Self in scope).
I'm only concerned about const items with bodies anyway since the whole idea is to prevent const eval's "bespoke" handling of "too generic" consts "being user observable" / load-bearing for program correctness (the other motivation being consts should behave like fns in this specific scenario) or rephrased "type based" > "value based".
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yeah type const stuff is whatever here. those should be handled by whatever normal:tm: thing we do for wfchecks of type system stuff
| Err(ErrorHandled::TooGeneric(_)) => self.visit_const_item_rhs(init), | ||
| // We've checked at the start that there aren't any non-lifetime params | ||
| // in scope. The const initializer can't possibly be too generic. | ||
| Err(ErrorHandled::TooGeneric(_)) => bug!(), |
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I'm unsure if this is true 🤔 I would expect it to be possible to get TooGeneric back when there are trivial bounds on the const item which prevent normalization in the const's body.
I guess that's fine for now anyhow... The whole setup here needs to be completely reworked to not evaluate stuff with false bounds or with generic parameters. And once that's done we should start evaluating with TypingEnv::fully_monomorphized which would fix that 🤔
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I intend to get back to that work.... somewhat soon, I think mGCA stuff is finally calming down so I should be able to put more time towards pushing on that again
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We generally don't want the initializer of free const items to get evaluated if they have any non-lifetime generic parameters. However, while I did account for that in HIR analysis & mono item collection (#136168 & #136429), I didn't account for reachability analysis so far which means that on main we still evaluate such items if they are public for example.
The closed PR #142293 from a year ago did address that as a byproduct but of course it wasn't merged since its primary goal was misguided. This PR extracts & improves upon the relevant parts of that PR which are necessary to fix said issue.
Follow up to #136168 & #136429.
Partially supersedes #142293.
Part of #113521.
r? @BoxyUwU