dont provide fwd declared params to cg defaults #86580

BoxyUwU · 2021-06-23T18:29:29Z

#![feature(const_evaluatable_checked, const_generics, const_generics_defaults)]
#![allow(incomplete_features)]

pub struct Bar<const N: usize, const M: usize = { N + 1 }>;
pub fn foo<const N1: usize>() -> Bar<N1> { loop {} }

fn main() {}

This PR makes this code no longer ICE, it was ICE'ing previously because when building substs for Bar<N1> we would subst the anon ct: ConstKind::Unevaluated({N + 1}, substs: [N, M]) with substs of [N1]. the anon const has forward declared params supplied though so we end up trying to substitute the provided M param which causes the ICE.

This PR doesn't handle the predicates of the const so

trait Foo<const N: usize> { const Assoc: usize; }
pub struct Bar<const N: usize = { <()>::Assoc }> where (): Foo<N>;

Resolves to <() as Foo<N>>::Assoc which can allow for using fwd declared params indirectly.

trait Foo<const N: usize> {}
struct Bar<const N: usize = { 2 + 3 }> where (): Foo<N>;

This code also ICEs under this PR because instantiating the default's predicates causes an ICE as predicates_of contains predicates with fwd declared params

PR was briefly discussed in this zulip thread

lcnr

while this does work for now, we probably want to implement these changes in generics_of instead to deal with the ParamEnv. We will need to do that to deal with unused substs in general.

I don't have a strong opinion on whether to merge this as is, so r=me if you think that it's desirable

BoxyUwU · 2021-07-09T16:20:43Z

(this PR needs the code to be wrapped in a if tcx.lazy_normalization() or wahtever so that we dont provide these generics without const_generics/const_evaluatable_checked feature gates)

edit: Done, and changes have been moved to generics_of and explicit_predicates_of

BoxyUwU · 2021-07-12T20:45:40Z

r? @nikomatsakis

compiler/rustc_typeck/src/collect.rs

compiler/rustc_typeck/src/outlives/mod.rs

nikomatsakis · 2021-07-20T21:27:45Z

@bors r+

bors · 2021-07-20T21:27:47Z

📌 Commit abfd44d has been approved by nikomatsakis

dont provide fwd declared params to cg defaults Fixes rust-lang#83938 ```rust #![feature(const_evaluatable_checked, const_generics, const_generics_defaults)] #![allow(incomplete_features)] pub struct Bar<const N: usize, const M: usize = { N + 1 }>; pub fn foo<const N1: usize>() -> Bar<N1> { loop {} } fn main() {} ``` This PR makes this code no longer ICE, it was ICE'ing previously because when building substs for `Bar<N1>` we would subst the anon ct: `ConstKind::Unevaluated({N + 1}, substs: [N, M])` with substs of `[N1]`. the anon const has forward declared params supplied though so we end up trying to substitute the provided `M` param which causes the ICE. This PR doesn't handle the predicates of the const so ```rust trait Foo<const N: usize> { const Assoc: usize; } pub struct Bar<const N: usize = { <()>::Assoc }> where (): Foo<N>; ``` Resolves to `<() as Foo<N>>::Assoc` which can allow for using fwd declared params indirectly. ```rust trait Foo<const N: usize> {} struct Bar<const N: usize = { 2 + 3 }> where (): Foo<N>; ``` This code also ICEs under this PR because instantiating the default's predicates causes an ICE as predicates_of contains predicates with fwd declared params PR was briefly discussed [in this zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/260443-project-const-generics/topic/evil.20preds.20in.20param.20env.20.2386580)

bors · 2021-07-21T03:32:01Z

⌛ Testing commit abfd44d with merge deab484024a324406ff1c8984f240ec0334a65a3...

BoxyUwU · 2021-07-21T14:20:10Z

@bors retry

bors · 2021-07-21T22:44:49Z

⌛ Testing commit abfd44d with merge 8e3359c9c54ca446b64a0aa00316f3f42fcda67a...

bors · 2021-07-21T23:18:14Z

💔 Test failed - checks-actions

BoxyUwU · 2021-07-22T20:18:16Z

@bors retry

BoxyUwU · 2021-07-24T18:01:14Z

@bors r=nikomatsakis

bors · 2021-07-24T18:01:15Z

📌 Commit d1e5e72 has been approved by nikomatsakis

bors · 2021-07-24T20:01:57Z

⌛ Testing commit d1e5e72 with merge d9aa287...

bors · 2021-07-24T22:30:51Z

☀️ Test successful - checks-actions
Approved by: nikomatsakis
Pushing d9aa287 to master...

rust-highfive assigned lcnr Jun 23, 2021

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lcnr approved these changes Jun 25, 2021

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BoxyUwU added 2 commits July 10, 2021 16:43

Dont provide all parent generics to cgdefaults

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Moves changes to explicit_preds_of/inferred_outlives_of/generics_of

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BoxyUwU force-pushed the cgd-subst-ice branch from 5a4432e to 57aa26c Compare July 10, 2021 16:36

redo tests

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BoxyUwU force-pushed the cgd-subst-ice branch from 57aa26c to e276b86 Compare July 10, 2021 16:39

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rust-highfive assigned nikomatsakis and unassigned lcnr Jul 12, 2021

lcnr reviewed Jul 13, 2021

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Put checking if anonct is a default into a method on hir map

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BoxyUwU force-pushed the cgd-subst-ice branch from e7c2d8c to 8c40360 Compare July 13, 2021 16:27

nikomatsakis requested changes Jul 15, 2021

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BoxyUwU force-pushed the cgd-subst-ice branch from 9ac61fb to 291aadc Compare July 16, 2021 00:12

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abfd44d

BoxyUwU force-pushed the cgd-subst-ice branch from 32e768d to abfd44d Compare July 17, 2021 11:00

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 20, 2021

Dylan-DPC-zz mentioned this pull request Jul 21, 2021

Rollup of 11 pull requests #87333

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d1e5e72

BoxyUwU force-pushed the cgd-subst-ice branch from c6d09c1 to d1e5e72 Compare July 24, 2021 16:33

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 24, 2021

bors merged commit d9aa287 into rust-lang:master Jul 24, 2021

rustbot added this to the 1.56.0 milestone Jul 24, 2021

lcnr added the A-const-generics Area: const generics (parameters and arguments) label Dec 11, 2021

lcnr mentioned this pull request Dec 11, 2021

Tracking issue for const generics (RFC 2000) #44580

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BoxyUwU mentioned this pull request Jan 22, 2022

Const Default with generic_const_exprs & super trait #93182

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BoxyUwU mentioned this pull request Mar 11, 2022

ICE on stable/nightly: const parameter C/#0 (Const { ty: (), val: Param(C/#0) }/0) out of range when substituting substs=[] #94846

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b-naber mentioned this pull request Aug 30, 2022

Const generics out of range when substituting substs=[] #101036

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This was referenced Jan 17, 2023

Include parent substs in substs argument in nominal_obligations when const param defaults exist #106847

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generic_const_exprs does not work properly with const/type param defaults #106994

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BoxyUwU mentioned this pull request Feb 13, 2023

Add Clause::ConstArgHasType #107965

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matthiaskrgr mentioned this pull request Sep 13, 2023

Compiler error involving HRTBs #115807

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dont provide fwd declared params to cg defaults #86580

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