Support const args in type dependent paths #71154
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cc @eddyb |
eddyb
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Apr 14, 2020
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I've converted the PR to a draft, and I will not be able to review it too soon. |
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Now also supports struct A;
impl A {
fn foo<const N: usize>() -> usize { N + 1 }
}
fn main() {
assert_eq!(A::foo::<7>(), 8);
} |
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☔ The latest upstream changes (presumably #71049) made this pull request unmergeable. Please resolve the merge conflicts. |
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Please keep it draft as per #71154 (comment). |
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☀️ Try build successful - checks-azure |
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Queued 2e0ee43e993a0a97edc6a0af1116bfbccdf1dd36 with parent a647c0c, future comparison URL. |
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Finished benchmarking try commit (2e0ee43e993a0a97edc6a0af1116bfbccdf1dd36): comparison url. |
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☔ The latest upstream changes (presumably #73830) made this pull request unmergeable. Please resolve the merge conflicts. |
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Will open a new PR in the next few weeks as I have to rewrite most of this anyways |
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in the next few weeks i guess time is relative #74113 |
bors
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Jul 15, 2020
Support const args in type dependent paths (Take 2) once more, except it is sound this time 🥰 previously rust-lang#71154 ----- ```rust #![feature(const_generics)] struct A; impl A { fn foo<const N: usize>(&self) -> usize { N } } struct B; impl B { fn foo<const N: usize>(&self) -> usize { 42 } } fn main() { let a = A; a.foo::<7>(); } ``` When calling `type_of` for generic const arguments, we now use the `TypeckTables` of the surrounding body to get the expected type. This alone causes cycle errors though, as we now have `typeck_tables_of(main)` -> `...` -> `type_of(main_ANON0 := 7)` -> `typeck_tables_of(main)` ⚡ (see rust-lang#68400 (comment)) To prevent this we must not call `type_of(const_arg)` during `typeck_tables_of`. This is achieved by calling `type_of(param_def_id)` instead. We have to somehow remember the `DefId` of the param through all of typeck, which is done using the struct `ty::WithOptConstParam<DefId>`, which replaces `DefId` where needed and contains an `Option<DefId>` to be able to store the const parameter in case it exists. Queries which are currently cached on disk are split into two variants: `query_name`(cached) and `query_name_(of|for)_const_arg`(not cached), with `query_name_of_const_arg` taking a pair `(did, param_did): (LocalDefId, DefId)`. For some queries a method `query_name_of_opt_const_arg` is added to `TyCtxt` which takes a `ty::WithOptConstParam` and either calls `query_name` or `query_name_of_const_arg` depending on the value of `const_param_did`. r? @eddyb @varkor
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When calling
type_offor generic const arguments, we now use theTypeckTablesof the surrounding body to get the expected type.This alone causes cycle errors though, as we now have
typeck_tables_of(main)->...->type_of(main_ANON0 := 7)->typeck_tables_of(main)⚡ (see #68400 (comment))To prevent this we must not call
type_of(const_arg)duringtypeck_tables_of. This is achieved bycalling
type_of(param_def_id)instead. As thisDefIdcan't always be easily known, I changed someDefIds toty::WithOptParam<DefId>which contains the relevant param id. This also changes some queries which may be called during typeck.To prevent us from computing these queries twice,
WithOptParammust always use the correctDefIdof the parameter. This means that it is either constructed using the new methodtcx.with_opt_param(def_id)or manually if and only if a paramDefIdis available.To simplify
WithOptParamcreation, I changedIntoQueryParamfrom private topub(crate).I only use the existing definition of
LocalDefId -> DefId.const_param_ofrequires the HIR, meaning that it can only return the correct parameterDefIdwhile compiling the crate containing the const argument.To fix this,
const_param_ofis called for all const arguments during analysis. (I currently usepar_body_ownerhere, as all const arguments should be a body afaik)This PR may have missed some
type_of(const_arg)during typeck. While this is unfortunate, these cases should only introduce cycle errors and not lead to miscompilations.We should not have to worry about these cases while merging this IMO.
r? @varkor
fixes #70507, fixes #69816, fixes #63695, fixes #61936, fixes #71516