instantiate_value_path: on `SelfCtor`, avoid unconstrained tyvars #69340

Centril · 2020-02-21T04:16:38Z

On Self(...) (that is, a Res::SelfCtor), do not use self.impl_self_ty(...). The problem with that method is that it creates unconstrained inference variables for type parameters in the impl (e.g. impl<T> S0<T>). These variables then eventually get substituted for something else when they come in contact with the expected type (e.g. S0<u8>) or merely the arguments passed to the tuple constructor (e.g. the 0 in Self(0)).

Instead of using self.impl_self_ty(...), we instead merely use let ty = self.normalize_ty(span, tcx.at(span).type_of(impl_def_id)); to get the rewritten res.

r? @eddyb

eddyb · 2020-02-21T14:01:15Z

... do not use self.impl_self_ty ...
The problem with that method is that it creates unconstrained inference variables for type parameters in the impl

Wait what? That's not what the name would suggest... If it creates inference variables it should have instantiate in the name IMO.

eddyb · 2020-02-21T14:17:14Z

src/librustc_typeck/check/mod.rs

@@ -5465,9 +5465,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
            .unwrap_or(false);

        let (res, self_ctor_substs) = if let Res::SelfCtor(impl_def_id) = res {
-            let ty = self.impl_self_ty(span, impl_def_id).ty;


Okay, I see, the .ty should've been a big warning flag (the other field is... substs).

Can you also change the call sites in check::method::suggest to just use tcx.type_of(impl_def_id)?
(EDIT: okay that wouldn't do the same thing, but I'm curious if that's necessary or if it actually makes things worse?)

And then maybe inline impl_self_ty into the only remaining use site (which is in check::method::confirm?).

If impl_self_ty was used more widely in check::method I'd suggest renaming it to instantiate_impl_self_ty and make it private to check::method. But it's not, so might as well get rid of it before this happens again.

I would prefer not dealing with it in this PR. I've filed #69489 for the follow-up.

eddyb · 2020-02-21T14:17:54Z

@bors try (I believe this deserves a check-only crater run)

bors · 2020-02-21T14:18:11Z

⌛ Trying commit 6cdb2d92aa973eaf4e84f5bf1846f0dba0540e1c with merge 9ff4d07208097950831ed4ea9d76feb1eafc8baa...

Centril · 2020-02-21T16:29:53Z

Note to self: Investigate whether this should be self.normalize_ty(tcx.type_of(...)) so that if the Self type is a projection or some such, we normalize it before seeing whether the normalized type is an ADT. (Also add a test case.)

EDIT: fixed.

bors · 2020-02-21T16:52:58Z

☀️ Try build successful - checks-azure
Build commit: 9ff4d07208097950831ed4ea9d76feb1eafc8baa (9ff4d07208097950831ed4ea9d76feb1eafc8baa)

Centril · 2020-02-21T17:02:56Z

@craterbot check

craterbot · 2020-02-21T17:03:00Z

👌 Experiment pr-69340 created and queued.
🤖 Automatically detected try build 9ff4d07208097950831ed4ea9d76feb1eafc8baa
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2020-02-21T17:03:04Z

🚧 Experiment pr-69340 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2020-02-24T05:39:27Z

🎉 Experiment pr-69340 is completed!
📊 21 regressed and 1 fixed (90999 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Centril · 2020-02-24T15:58:14Z

Crater triage:

There are 6 root regressions.
- 1 was in my own crate and has already been fixed (with a point release).
- 4 has already merged regression fixes.
- The 1 remaining has a PR open fixing the problem.

Centril · 2020-02-26T18:31:24Z

I added a call to normalize_ty as well to handle projections, as this was previously allowed, and is allowed when using Self { ... }.

I believe this should be ready to go as there's a single remaining regression which has an open PR.
r? @petrochenkov

pnkfelix · 2020-02-27T15:20:17Z

discussed at T-compiler meeting. Delaying question of whether to beta backport to next week's meeting.

nikomatsakis · 2020-02-27T15:22:11Z

@bors r+

My two cents:

The change would be difficult, from a technical perspective, to do a future-compatibility warning for.

The impact is non-trivial but manageable, and @Centril did a great job of opening PRs (which have been merged). However, this doesn't mean we're "all set", as those changes still have to make their way into new releases (ideally, point releases), and that usually takes some time.

I'm inclined to approve this, but I think we want to be on the lookout for bug reports from folks that are affected "in the wild".

I'm somewhat inclined not to backport, so as to give people a bit more time to adapt before it reaches a stable release, but it depends on how many regression reports we receive after landing.

bors · 2020-02-27T15:23:29Z

📌 Commit 6672a04 has been approved by nikomatsakis

Centril · 2020-02-27T15:25:55Z

r? @nikomatsakis

@ghost

Rollup of 10 pull requests Successful merges: - #68989 (Update RELEASES.md for 1.42.0) - #69340 (instantiate_value_path: on `SelfCtor`, avoid unconstrained tyvars) - #69384 (parser: `token` -> `normalized_token`, `nonnormalized_token` -> `token`) - #69452 (typeck: use `Pattern` obligation cause more for better diagnostics) - #69481 (use char instead of &str for single char patterns) - #69522 (error_derive_forbidden_on_non_adt: be more graceful) - #69538 (Stabilize `boxed_slice_try_from`) - #69539 (late resolve, visit_fn: bail early if there's no body.) - #69541 (Remove unneeded calls to format!()) - #69547 (remove redundant clones, references to operands, explicit boolean comparisons and filter(x).next() calls.) Failed merges: r? @ghost

pnkfelix · 2020-03-05T15:30:40Z

discussed in T-compiler meeting. declined for beta-backport.

Pkgsrc changes: * Bump rust bootstrap version to 1.42.0, except for Darwin/i686 where the bootstrap is not (yet?) available. Upstream changes: Version 1.43.0 (2020-04-23) ========================== Language -------- - [Fixed using binary operations with `&{number}` (e.g. `&1.0`) not having the type inferred correctly.][68129] - [Attributes such as `#[cfg()]` can now be used on `if` expressions.][69201] **Syntax only changes** - [Allow `type Foo: Ord` syntactically.][69361] - [Fuse associated and extern items up to defaultness.][69194] - [Syntactically allow `self` in all `fn` contexts.][68764] - [Merge `fn` syntax + cleanup item parsing.][68728] - [`item` macro fragments can be interpolated into `trait`s, `impl`s, and `extern` blocks.][69366] For example, you may now write: ```rust macro_rules! mac_trait { ($i:item) => { trait T { $i } } } mac_trait! { fn foo() {} } ``` These are still rejected *semantically*, so you will likely receive an error but these changes can be seen and parsed by macros and conditional compilation. Compiler -------- - [You can now pass multiple lint flags to rustc to override the previous flags.][67885] For example; `rustc -D unused -A unused-variables` denies everything in the `unused` lint group except `unused-variables` which is explicitly allowed. However, passing `rustc -A unused-variables -D unused` denies everything in the `unused` lint group **including** `unused-variables` since the allow flag is specified before the deny flag (and therefore overridden). - [rustc will now prefer your system MinGW libraries over its bundled libraries if they are available on `windows-gnu`.][67429] - [rustc now buffers errors/warnings printed in JSON.][69227] Libraries --------- - [`Arc<[T; N]>`, `Box<[T; N]>`, and `Rc<[T; N]>`, now implement `TryFrom<Arc<[T]>>`,`TryFrom<Box<[T]>>`, and `TryFrom<Rc<[T]>>` respectively.][69538] **Note** These conversions are only available when `N` is `0..=32`. - [You can now use associated constants on floats and integers directly, rather than having to import the module.][68952] e.g. You can now write `u32::MAX` or `f32::NAN` with no imports. - [`u8::is_ascii` is now `const`.][68984] - [`String` now implements `AsMut<str>`.][68742] - [Added the `primitive` module to `std` and `core`.][67637] This module reexports Rust's primitive types. This is mainly useful in macros where you want avoid these types being shadowed. - [Relaxed some of the trait bounds on `HashMap` and `HashSet`.][67642] - [`string::FromUtf8Error` now implements `Clone + Eq`.][68738] Stabilized APIs --------------- - [`Once::is_completed`] - [`f32::LOG10_2`] - [`f32::LOG2_10`] - [`f64::LOG10_2`] - [`f64::LOG2_10`] - [`iter::once_with`] Cargo ----- - [You can now set config `[profile]`s in your `.cargo/config`, or through your environment.][cargo/7823] - [Cargo will now set `CARGO_BIN_EXE_<name>` pointing to a binary's executable path when running integration tests or benchmarks.][cargo/7697] `<name>` is the name of your binary as-is e.g. If you wanted the executable path for a binary named `my-program`you would use `env!("CARGO_BIN_EXE_my-program")`. Misc ---- - [Certain checks in the `const_err` lint were deemed unrelated to const evaluation][69185], and have been moved to the `unconditional_panic` and `arithmetic_overflow` lints. Compatibility Notes ------------------- - [Having trailing syntax in the `assert!` macro is now a hard error.][69548] This has been a warning since 1.36.0. - [Fixed `Self` not having the correctly inferred type.][69340] This incorrectly led to some instances being accepted, and now correctly emits a hard error. [69340]: rust-lang/rust#69340 Internal Only ------------- These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of `rustc` and related tools. - [All components are now built with `opt-level=3` instead of `2`.][67878] - [Improved how rustc generates drop code.][67332] - [Improved performance from `#[inline]`-ing certain hot functions.][69256] - [traits: preallocate 2 Vecs of known initial size][69022] - [Avoid exponential behaviour when relating types][68772] - [Skip `Drop` terminators for enum variants without drop glue][68943] - [Improve performance of coherence checks][68966] - [Deduplicate types in the generator witness][68672] - [Invert control in struct_lint_level.][68725] [67332]: rust-lang/rust#67332 [67429]: rust-lang/rust#67429 [67637]: rust-lang/rust#67637 [67642]: rust-lang/rust#67642 [67878]: rust-lang/rust#67878 [67885]: rust-lang/rust#67885 [68129]: rust-lang/rust#68129 [68672]: rust-lang/rust#68672 [68725]: rust-lang/rust#68725 [68728]: rust-lang/rust#68728 [68738]: rust-lang/rust#68738 [68742]: rust-lang/rust#68742 [68764]: rust-lang/rust#68764 [68772]: rust-lang/rust#68772 [68943]: rust-lang/rust#68943 [68952]: rust-lang/rust#68952 [68966]: rust-lang/rust#68966 [68984]: rust-lang/rust#68984 [69022]: rust-lang/rust#69022 [69185]: rust-lang/rust#69185 [69194]: rust-lang/rust#69194 [69201]: rust-lang/rust#69201 [69227]: rust-lang/rust#69227 [69548]: rust-lang/rust#69548 [69256]: rust-lang/rust#69256 [69361]: rust-lang/rust#69361 [69366]: rust-lang/rust#69366 [69538]: rust-lang/rust#69538 [cargo/7823]: rust-lang/cargo#7823 [cargo/7697]: rust-lang/cargo#7697 [`Once::is_completed`]: https://doc.rust-lang.org/std/sync/struct.Once.html#method.is_completed [`f32::LOG10_2`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG10_2.html [`f32::LOG2_10`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG2_10.html [`f64::LOG10_2`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG10_2.html [`f64::LOG2_10`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG2_10.html [`iter::once_with`]: https://doc.rust-lang.org/std/iter/fn.once_with.html

rust-highfive assigned eddyb Feb 21, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 21, 2020

Centril added beta-nominated Nominated for backporting to the compiler in the beta channel. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 21, 2020

eddyb reviewed Feb 21, 2020

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craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 21, 2020

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Feb 24, 2020

instantiate_value_path: .impl_self_ty -> .type_of

6672a04

Centril force-pushed the self-ctor-normalize branch from 6cdb2d9 to 6672a04 Compare February 26, 2020 18:26

Centril mentioned this pull request Feb 26, 2020

Audit uses of FnCtxt::impl_self_ty #69489

Closed

rust-highfive unassigned eddyb Feb 26, 2020

rust-highfive assigned petrochenkov Feb 26, 2020

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 Feb 27, 2020

rust-highfive assigned nikomatsakis and unassigned petrochenkov Feb 27, 2020

Centril mentioned this pull request Feb 28, 2020

Rollup of 10 pull requests #69555

Merged

bors merged commit 76fe449 into rust-lang:master Feb 28, 2020

Centril deleted the self-ctor-normalize branch February 28, 2020 21:21

rye mentioned this pull request Mar 1, 2020

Possible regression on use of Self in generics ("mismatched types") #69611

Closed

pnkfelix removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Mar 5, 2020

This was referenced Mar 26, 2020

regression: mismatched types (lifetimes) #70443

Closed

regression: mismatched types #70444

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Mark-Simulacrum mentioned this pull request Mar 26, 2020

Update RELEASES.md for 1.43.0 #70354

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dwrensha mentioned this pull request Oct 14, 2021

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0' #89868

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instantiate_value_path: on `SelfCtor`, avoid unconstrained tyvars #69340

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instantiate_value_path: on SelfCtor, avoid unconstrained tyvars #69340

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instantiate_value_path: on `SelfCtor`, avoid unconstrained tyvars #69340

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