Parse the syntax described in RFC 2632 #67820
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oli-obk
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| impl const T for S {} | ||
| //~^ ERROR const trait impls are experimental | ||
| //~| ERROR const trait impls are experimental |
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That's fine for now. It'll immediately go away when the feature gate has some logic, so...
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I switched to "not yet implemented" for the non-feature gated errors anyways. It made it easier to track see when I had forgotten a feature gate in the tests.
| trait T {} | ||
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| // An inherent impl for a trait object of `?const T`. | ||
| impl ?const T {} |
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Not sure if this should ever be accepted. Probably not without an epoch doing other const things. Please make this a hard error for now
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But I don't think it should be a hard error under #[cfg(FALSE)]. Make sure to test syntax independently of semantics, and preferably in one file, as a // check-pass test.
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I'd also like to see tests that includes impl Trait in various positions (syntactically vs. semantically -- different tests).
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?const is now forbidden in impl Trait and trait objects.
| trait Trait {} | ||
| struct Foo<T: Trait>(T); | ||
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| const fn new_foo<T: ?const Trait>(t: T) -> Foo<T> { |
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I think the tests with and without the feature gate should have the same content so we are testing all the syntax in both situations
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I reorganized the tests a bit and am using the revisions trick for now to guarantee this.
Centril
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Jan 3, 2020
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| // compile-flags: -Z parse-only | |||
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Why is this flag necessary?
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| // parse-fail | |||
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Remove this. There's no such directive.
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And also this doesn't seem to be true of the test. The errors below are not parser errors.
| trait T {} | ||
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| // An inherent impl for a trait object of `?const T`. | ||
| impl ?const T {} |
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But I don't think it should be a hard error under #[cfg(FALSE)]. Make sure to test syntax independently of semantics, and preferably in one file, as a // check-pass test.
| trait T {} | ||
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| // An inherent impl for a trait object of `?const T`. | ||
| impl ?const T {} |
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I'd also like to see tests that includes impl Trait in various positions (syntactically vs. semantically -- different tests).
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@Centril I added checks for |
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Centril
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| struct S; | ||
| impl T for S {} | ||
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| fn rpit() -> impl ?const T { S } |
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Seems like we came away with different interpretations of what Oliver said.
I think this would be perfectly well defined and semantically sane (same with dyn ?const Trait).
After some more reflection, I think the semantic property one would want is that ?const is legal if and only if we are in a const-by-default context (const fn) or const Trait for { ... }`). However, if you want to get this landed quicker, I'm fine with this for now (but leave the comment visible).
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While these would be fine in the future, having them be a hard error for now and giving them their own feature gates in the future seems the best way forward to me. The RFC specifically talked about a minimal version that does not include impl Trait at all
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After porting these checks to AST validation, I also decided to error when they are found on trait bounds (e.g., trait T: ?const Super {}). While this is not explicitly called out as a future extension by the RFC, it will not be useful until const trait definitions have some meaning.
oli-obk
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Jan 4, 2020
| struct S; | ||
| impl T for S {} | ||
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| fn rpit() -> impl ?const T { S } |
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While these would be fine in the future, having them be a hard error for now and giving them their own feature gates in the future seems the best way forward to me. The RFC specifically talked about a minimal version that does not include impl Trait at all
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Jan 5, 2020
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@bors r+ |
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📌 Commit 19f74cb has been approved by |
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Parse the syntax described in RFC 2632 This adds support for both `impl const Trait for Ty` and `?const Trait` bound syntax from rust-lang/rfcs#2632 to the parser. For now, both modifiers end up in a newly-added `constness` field on `ast::TraitRef`, although this may change once the implementation is fleshed out. I was planning on using `delay_span_bug` when this syntax is encountered during lowering, but I can't write `should-ice` UI tests. I emit a normal error instead, which causes duplicates when the feature gate is not enabled (see the `.stderr` files for the feature gate tests). Not sure what the desired approach is; Maybe just do nothing when the syntax is encountered with the feature gate is enabled? @oli-obk I went with `const_trait_impl` and `const_trait_bound_opt_out` for the names of these features. Are these to your liking? cc rust-lang#67792 rust-lang#67794 r? @Centril
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☔ The latest upstream changes (presumably #67770) made this pull request unmergeable. Please resolve the merge conflicts. |
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Rollup of 10 pull requests Successful merges: - #67774 (Try statx for all linux-gnu target.) - #67781 (Move `is_min_const_fn` query to librustc_mir.) - #67798 (Remove wrong advice about spin locks from `spin_loop_hint` docs) - #67849 (Add a check for swapped words when we can't find an identifier) - #67875 (Distinguish between private items and hidden items in rustdoc) - #67887 (`Option::{expect,unwrap}` and `Result::{expect, expect_err, unwrap, unwrap_err}` have `#[track_caller]`) - #67955 (rustdoc: Remove more `#[doc(cfg(..))]` duplicates) - #67977 (Updates for VxWorks) - #67985 (Remove insignificant notes from CStr documentation) - #68003 (ci: fix wrong shared.sh import for publish_toolstate) Failed merges: - #67820 (Parse the syntax described in RFC 2632) - #67979 (Move `intravisit` => `rustc_hir` + misc cleanup) r? @ghost
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Rollup of 10 pull requests Successful merges: - #67774 (Try statx for all linux-gnu target.) - #67781 (Move `is_min_const_fn` query to librustc_mir.) - #67798 (Remove wrong advice about spin locks from `spin_loop_hint` docs) - #67849 (Add a check for swapped words when we can't find an identifier) - #67875 (Distinguish between private items and hidden items in rustdoc) - #67887 (`Option::{expect,unwrap}` and `Result::{expect, expect_err, unwrap, unwrap_err}` have `#[track_caller]`) - #67955 (rustdoc: Remove more `#[doc(cfg(..))]` duplicates) - #67977 (Updates for VxWorks) - #67985 (Remove insignificant notes from CStr documentation) - #68003 (ci: fix wrong shared.sh import for publish_toolstate) Failed merges: - #67820 (Parse the syntax described in RFC 2632) - #67979 (Move `intravisit` => `rustc_hir` + misc cleanup) r? @ghost
This is used for both the `?const` syntax in bounds as well as the `impl const Trait` syntax. I also considered handling these separately by adding a variant of `TraitBoundModifier` and a field to `ItemKind::Impl`, but this approach was less intrusive.
The grammar also handles `?const ?Trait` even though this is semantically redundant.
This means the new syntax will always fail to compile, even when the feature gate is enabled. These checks will be removed in a later PR once the implementation is done.
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@bors r=oli-obk |
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📌 Commit fd1c003 has been approved by |
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Parse the syntax described in RFC 2632 This adds support for both `impl const Trait for Ty` and `?const Trait` bound syntax from rust-lang/rfcs#2632 to the parser. For now, both modifiers end up in a newly-added `constness` field on `ast::TraitRef`, although this may change once the implementation is fleshed out. I was planning on using `delay_span_bug` when this syntax is encountered during lowering, but I can't write `should-ice` UI tests. I emit a normal error instead, which causes duplicates when the feature gate is not enabled (see the `.stderr` files for the feature gate tests). Not sure what the desired approach is; Maybe just do nothing when the syntax is encountered with the feature gate is enabled? @oli-obk I went with `const_trait_impl` and `const_trait_bound_opt_out` for the names of these features. Are these to your liking? cc rust-lang#67792 rust-lang#67794 r? @Centril
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Parse the syntax described in RFC 2632 This adds support for both `impl const Trait for Ty` and `?const Trait` bound syntax from rust-lang/rfcs#2632 to the parser. For now, both modifiers end up in a newly-added `constness` field on `ast::TraitRef`, although this may change once the implementation is fleshed out. I was planning on using `delay_span_bug` when this syntax is encountered during lowering, but I can't write `should-ice` UI tests. I emit a normal error instead, which causes duplicates when the feature gate is not enabled (see the `.stderr` files for the feature gate tests). Not sure what the desired approach is; Maybe just do nothing when the syntax is encountered with the feature gate is enabled? @oli-obk I went with `const_trait_impl` and `const_trait_bound_opt_out` for the names of these features. Are these to your liking? cc rust-lang#67792 rust-lang#67794 r? @Centril
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Rollup of 6 pull requests Successful merges: - #66463 (Point at opaque and closure type definitions in type errors) - #67501 (Reduce special treatment for zsts) - #67820 (Parse the syntax described in RFC 2632) - #67922 (rustc_ast_lowering: misc cleanup & rustc dep reductions) - #68071 (Extend support of `_` in type parameters) - #68073 (expect `fn` after `const unsafe` / `const extern`) Failed merges: r? @ghost
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This adds support for both
impl const Trait for Tyand?const Traitbound syntax from rust-lang/rfcs#2632 to the parser. For now, both modifiers end up in a newly-addedconstnessfield onast::TraitRef, although this may change once the implementation is fleshed out.I was planning on using
delay_span_bugwhen this syntax is encountered during lowering, but I can't writeshould-iceUI tests. I emit a normal error instead, which causes duplicates when the feature gate is not enabled (see the.stderrfiles for the feature gate tests). Not sure what the desired approach is; Maybe just do nothing when the syntax is encountered with the feature gate is enabled?@oli-obk I went with
const_trait_implandconst_trait_bound_opt_outfor the names of these features. Are these to your liking?cc #67792 #67794
r? @Centril