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Move object lifetime default computation #97839

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Move object lifetime default computation #97839

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cjgillot
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@cjgillot cjgillot commented Jun 7, 2022

Split from #97393

r? @jackh726

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 7, 2022
@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 7, 2022
cjgillot
cjgillot commented Jun 7, 2022
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compiler/rustc_typeck/src/collect/object_lifetime_defaults.rs
}
ObjectLifetimeDefault::Static => Some(Region::Static),
ObjectLifetimeDefault::Param(def_id) => {
let index = generics.param_def_id_to_index[&def_id];
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I'm not sure this is the right index here.

jackh726
jackh726 reviewed Jun 7, 2022
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Some initial comments.

compiler/rustc_resolve/src/late/lifetimes.rs Outdated
Comment on lines 775 to 777
// use the object lifetime defaulting
// rules. So e.g., `Box<dyn Debug>` becomes
// `Box<dyn Debug + 'static>`.
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This comment should be removed, I think.

compiler/rustc_typeck/src/astconv/mod.rs Show resolved Hide resolved
compiler/rustc_typeck/src/astconv/mod.rs Show resolved Hide resolved
compiler/rustc_typeck/src/collect.rs Outdated
Comment on lines 1351 to 1356
if let hir::LifetimeName::ImplicitObjectLifetimeDefault = lt.name {
return;
}
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Hmm. Is this true? I could imagine a scenario like

struct Foo<'a, T: 'a> {}
trait Bar {}

let _: for<'x> fn(Foo<'x, dyn Bar>);

Does that apply here?

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This code is only used for function item-likes.

I agree, this is slightly wrong. However, this cannot cause a bug: ImplicitObjectLifetimeDefault can only reference a lifetime from an outer & reference, a generic argument, or 'static. So the lifetime this references has already been seen by the visitor.

However, this whole visitor will be useless once #97720 lands. All the lifetimes in a function's signature will be generic parameters, so only the loop in has_late_bound_regions will be required.

compiler/rustc_middle/src/query/mod.rs Outdated
/// Fetch the lifetimes for all the trait objects in an item-like.
query object_lifetime_map(_: LocalDefId) -> FxHashMap<ItemLocalId, Region> {
storage(ArenaCacheSelector<'tcx>)
desc { "looking up lifetime defaults for a region on an item" }
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Is this description correct?

It's probably worth elaborating a bit in a comment what the different between object_lifetime_map and object_lifetime_defaults are.

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It's probably worth elaborating a bit in a comment what the different between object_lifetime_map and object_lifetime_defaults are.

This is still relevant

src/test/ui/issues/issue-41139.rs Outdated
//~^ ERROR expected function, found `&dyn Fn() -> (dyn Trait + 'static)`
//~^ ERROR expected function, found `&dyn Fn() -> dyn Trait`
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Why did this change? Not a huge deal, but would be nice to know why

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This is a bug.

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Wait, do you mean the existing test is a bug? Or the new output is?

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The new output is buggy.

@cjgillot cjgillot force-pushed the object-lifetime-default-small branch from fa5dff6 to fc2713e Compare June 8, 2022 17:56
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@cjgillot cjgillot force-pushed the object-lifetime-default-small branch from fc2713e to 5d5eda8 Compare June 8, 2022 19:43
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Gonna try to take another look at this PR this weekend.

jackh726
jackh726 approved these changes Jun 13, 2022
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Looking pretty good. Just two small comments. Also, can you merge some commits (pacify tidy, fix comments and query description) into other relevant commits. Not required, but would be nice. r=me after review addressed

compiler/rustc_middle/src/query/mod.rs Outdated
/// Fetch the lifetimes for all the trait objects in an item-like.
query object_lifetime_map(_: LocalDefId) -> FxHashMap<ItemLocalId, Region> {
storage(ArenaCacheSelector<'tcx>)
desc { "looking up lifetime defaults for a region on an item" }
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It's probably worth elaborating a bit in a comment what the different between object_lifetime_map and object_lifetime_defaults are.

This is still relevant

compiler/rustc_typeck/src/astconv/mod.rs Outdated
let tcx = self.tcx();
if let hir::LifetimeName::ImplicitObjectLifetimeDefault = lifetime.name {
panic!(
"ImplicitObjectLifetimeDefault should not handled separately from ast_region_to_region."
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s/not/be?

@cjgillot cjgillot force-pushed the object-lifetime-default-small branch from 5d5eda8 to 1f535a0 Compare June 14, 2022 19:23
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@cjgillot cjgillot force-pushed the object-lifetime-default-small branch from 1f535a0 to 37f42cb Compare June 14, 2022 19:44
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I'm having doubts whether this is the right direction. I'm marking this as blocked until I have a proper idea of where we are going.

@cjgillot cjgillot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 14, 2022
@jackh726 jackh726 mentioned this pull request Jun 26, 2022
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bors commented Jul 25, 2022

☔ The latest upstream changes (presumably #97313) made this pull request unmergeable. Please resolve the merge conflicts.

@cjgillot cjgillot closed this Jul 27, 2022
@cjgillot cjgillot deleted the object-lifetime-default-small branch July 27, 2022 20:10
@cjgillot cjgillot mentioned this pull request Jul 27, 2022
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Dylan-DPC added a commit to Dylan-DPC/rust that referenced this pull request Aug 29, 2022
@Dylan-DPC
Rollup merge of rust-lang#99821 - cjgillot:ast-lifetimes-2, r=compile…
8bd80ab 
…r-errors

Remove separate indexing of early-bound regions

~Based on rust-lang#99728

This PR copies some modifications from rust-lang#97839 around object lifetime defaults.
These modifications allow to stop counting generic parameters during lifetime resolution, and rely on the indexing given by `rustc_typeck::collect`.
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this pull request Aug 29, 2022
@Dylan-DPC
Rollup merge of rust-lang#99821 - cjgillot:ast-lifetimes-2, r=compile…
5555e13 
…r-errors

Remove separate indexing of early-bound regions

~Based on rust-lang#99728

This PR copies some modifications from rust-lang#97839 around object lifetime defaults.
These modifications allow to stop counting generic parameters during lifetime resolution, and rely on the indexing given by `rustc_typeck::collect`.
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