Partially implement RFC 1647 (Self in impl headers)
#38920
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FWIW I had solved the cycle problem a few months back (eddyb@204fdb2) and I'm planning to publish that as the next (and final?) PR after #38813. However I'm taking a (yet another) detour through doing lifetime elision syntactically (w/ name-resolved definitions but nothing based on type/trait resolution), which would allow a more efficient implementation of my fixpoint algorithm (it's backtracking atm so |
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So do we want to wait here for some of @eddyb's work to land instead? |
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@nikomatsakis |
petrochenkov
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Self in impl headers)Self in impl headers)
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I'll rebase this tomorrow. |
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Rebased. |
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r? @eddyb -- he's been in this area so is best person to review |
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@bors r+ |
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📌 Commit f9bdf34 has been approved by |
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Partially implement RFC 1647 (`Self` in impl headers)
The name resolution part is easy, but the typeck part contains an unexpected problem.
It turns out that `Self` type *depends* on bounds and `where` clauses, so we need to convert them first to determine what the `Self` type is! If bounds/`where` clauses can refer to `Self` then we have a cyclic dependency.
This is required to support impls like this:
```
// Found in libcollections
impl<I: IntoIterator> SpecExtend<I> for LinkedList<I::Item> { .... }
^^^^^ associated type `Item` is found using information from bounds
```
I'm not yet sure how to resolve this issue.
One possible solution (that feels hacky) is to make two passes over generics - first collect predicates ignoring everything involving `Self`, then determine `Self`, then collect predicates again without ignoring anything. (Some kind of lazy on-demand checking or something looks like a proper solution.)
This patch in its current state doesn't solve the problem with `Self` in bounds, so the only observable things it does is improving error messages and supporting `impl Trait<Self> for Type {}`.
There's also a question about feature gating. It's non-trivial to *detect* "newly resolved" `Self`s to feature gate them, but it's simple to *enable* the new resolution behavior when the feature gate is already specified. Alternatively this can be considered a bug fix and merged without a feature gate.
cc #38864
r? @nikomatsakis
cc @eddyb
Whitespace ignoring diff https://github.com/rust-lang/rust/pull/38920/files?w=1
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☀️ Test successful - status-appveyor, status-travis |
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| ty.subst(tcx, free_substs) | ||
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| // FIXME: Self type is not always computed when we are here because type parameter | ||
| // bounds may affect Self type and have to be converted before it. |
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I was working on the on-demand stuff and I just realized this can be made to work with AstConv::get_item_type.
In all fairness, ItemImpl is not hooked up to that in rustc_typeck::collect because of predicate complications, that are fixed on this branch I'm playing with (even if you can't get it from tcx.item_type, that's not needed here).
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Version 1.16.0 (2017-03-16) =========================== Language -------- * Lifetimes in statics and consts default to `'static`. [RFC 1623] * [The compiler's `dead_code` lint now accounts for type aliases][38051]. * [Uninhabitable enums (those without any variants) no longer permit wildcard match patterns][38069] * [Clean up semantics of `self` in an import list][38313] * [`Self` may appear in `impl` headers][38920] * [`Self` may appear in struct expressions][39282] Compiler -------- * [`rustc` now supports `--emit=metadata`, which causes rustc to emit a `.rmeta` file containing only crate metadata][38571]. This can be used by tools like the Rust Language Service to perform metadata-only builds. * [Levenshtein based typo suggestions now work in most places, while previously they worked only for fields and sometimes for local variables][38927]. Together with the overhaul of "no resolution"/"unexpected resolution" errors (#[38154]) they result in large and systematic improvement in resolution diagnostics. * [Fix `transmute::<T, U>` where `T` requires a bigger alignment than `U`][38670] * [rustc: use -Xlinker when specifying an rpath with ',' in it][38798] * [`rustc` no longer attempts to provide "consider using an explicit lifetime" suggestions][37057]. They were inaccurate. Stabilized APIs --------------- * [`VecDeque::truncate`] * [`VecDeque::resize`] * [`String::insert_str`] * [`Duration::checked_add`] * [`Duration::checked_sub`] * [`Duration::checked_div`] * [`Duration::checked_mul`] * [`str::replacen`] * [`str::repeat`] * [`SocketAddr::is_ipv4`] * [`SocketAddr::is_ipv6`] * [`IpAddr::is_ipv4`] * [`IpAddr::is_ipv6`] * [`Vec::dedup_by`] * [`Vec::dedup_by_key`] * [`Result::unwrap_or_default`] * [`<*const T>::wrapping_offset`] * [`<*mut T>::wrapping_offset`] * `CommandExt::creation_flags` * [`File::set_permissions`] * [`String::split_off`] Libraries --------- * [`[T]::binary_search` and `[T]::binary_search_by_key` now take their argument by `Borrow` parameter][37761] * [All public types in std implement `Debug`][38006] * [`IpAddr` implements `From<Ipv4Addr>` and `From<Ipv6Addr>`][38327] * [`Ipv6Addr` implements `From<[u16; 8]>`][38131] * [Ctrl-Z returns from `Stdin.read()` when reading from the console on Windows][38274] * [std: Fix partial writes in `LineWriter`][38062] * [std: Clamp max read/write sizes on Unix][38062] * [Use more specific panic message for `&str` slicing errors][38066] * [`TcpListener::set_only_v6` is deprecated][38304]. This functionality cannot be achieved in std currently. * [`writeln!`, like `println!`, now accepts a form with no string or formatting arguments, to just print a newline][38469] * [Implement `iter::Sum` and `iter::Product` for `Result`][38580] * [Reduce the size of static data in `std_unicode::tables`][38781] * [`char::EscapeDebug`, `EscapeDefault`, `EscapeUnicode`, `CaseMappingIter`, `ToLowercase`, `ToUppercase`, implement `Display`][38909] * [`Duration` implements `Sum`][38712] * [`String` implements `ToSocketAddrs`][39048] Cargo ----- * [The `cargo check` command does a type check of a project without building it][cargo/3296] * [crates.io will display CI badges from Travis and AppVeyor, if specified in Cargo.toml][cargo/3546] * [crates.io will display categories listed in Cargo.toml][cargo/3301] * [Compilation profiles accept integer values for `debug`, in addition to `true` and `false`. These are passed to `rustc` as the value to `-C debuginfo`][cargo/3534] * [Implement `cargo --version --verbose`][cargo/3604] * [All builds now output 'dep-info' build dependencies compatible with make and ninja][cargo/3557] * [Build all workspace members with `build --all`][cargo/3511] * [Document all workspace members with `doc --all`][cargo/3515] * [Path deps outside workspace are not members][cargo/3443] Misc ---- * [`rustdoc` has a `--sysroot` argument that, like `rustc`, specifies the path to the Rust implementation][38589] * [The `armv7-linux-androideabi` target no longer enables NEON extensions, per Google's ABI guide][38413] * [The stock standard library can be compiled for Redox OS][38401] * [Rust has initial SPARC support][38726]. Tier 3. No builds available. * [Rust has experimental support for Nvidia PTX][38559]. Tier 3. No builds available. * [Fix backtraces on i686-pc-windows-gnu by disabling FPO][39379] Compatibility Notes ------------------- * [Uninhabitable enums (those without any variants) no longer permit wildcard match patterns][38069] * In this release, references to uninhabited types can not be pattern-matched. This was accidentally allowed in 1.15. * [The compiler's `dead_code` lint now accounts for type aliases][38051]. * [Ctrl-Z returns from `Stdin.read()` when reading from the console on Windows][38274] * [Clean up semantics of `self` in an import list][38313] [37057]: rust-lang/rust#37057 [37761]: rust-lang/rust#37761 [38006]: rust-lang/rust#38006 [38051]: rust-lang/rust#38051 [38062]: rust-lang/rust#38062 [38062]: rust-lang/rust#38622 [38066]: rust-lang/rust#38066 [38069]: rust-lang/rust#38069 [38131]: rust-lang/rust#38131 [38154]: rust-lang/rust#38154 [38274]: rust-lang/rust#38274 [38304]: rust-lang/rust#38304 [38313]: rust-lang/rust#38313 [38314]: rust-lang/rust#38314 [38327]: rust-lang/rust#38327 [38401]: rust-lang/rust#38401 [38413]: rust-lang/rust#38413 [38469]: rust-lang/rust#38469 [38559]: rust-lang/rust#38559 [38571]: rust-lang/rust#38571 [38580]: rust-lang/rust#38580 [38589]: rust-lang/rust#38589 [38670]: rust-lang/rust#38670 [38712]: rust-lang/rust#38712 [38726]: rust-lang/rust#38726 [38781]: rust-lang/rust#38781 [38798]: rust-lang/rust#38798 [38909]: rust-lang/rust#38909 [38920]: rust-lang/rust#38920 [38927]: rust-lang/rust#38927 [39048]: rust-lang/rust#39048 [39282]: rust-lang/rust#39282 [39379]: rust-lang/rust#39379 [`<*const T>::wrapping_offset`]: https://doc.rust-lang.org/std/primitive.pointer.html#method.wrapping_offset [`<*mut T>::wrapping_offset`]: https://doc.rust-lang.org/std/primitive.pointer.html#method.wrapping_offset [`Duration::checked_add`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.checked_add [`Duration::checked_div`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.checked_div [`Duration::checked_mul`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.checked_mul [`Duration::checked_sub`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.checked_sub [`File::set_permissions`]: https://doc.rust-lang.org/std/fs/struct.File.html#method.set_permissions [`IpAddr::is_ipv4`]: https://doc.rust-lang.org/std/net/enum.IpAddr.html#method.is_ipv4 [`IpAddr::is_ipv6`]: https://doc.rust-lang.org/std/net/enum.IpAddr.html#method.is_ipv6 [`Result::unwrap_or_default`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.unwrap_or_default [`SocketAddr::is_ipv4`]: https://doc.rust-lang.org/std/net/enum.SocketAddr.html#method.is_ipv4 [`SocketAddr::is_ipv6`]: https://doc.rust-lang.org/std/net/enum.SocketAddr.html#method.is_ipv6 [`String::insert_str`]: https://doc.rust-lang.org/std/string/struct.String.html#method.insert_str [`String::split_off`]: https://doc.rust-lang.org/std/string/struct.String.html#method.split_off [`Vec::dedup_by_key`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.dedup_by_key [`Vec::dedup_by`]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.dedup_by [`VecDeque::resize`]: https://doc.rust-lang.org/std/collections/vec_deque/struct.VecDeque.html#method.resize [`VecDeque::truncate`]: https://doc.rust-lang.org/std/collections/vec_deque/struct.VecDeque.html#method.truncate [`str::repeat`]: https://doc.rust-lang.org/std/primitive.str.html#method.repeat [`str::replacen`]: https://doc.rust-lang.org/std/primitive.str.html#method.replacen [cargo/3296]: rust-lang/cargo#3296 [cargo/3301]: rust-lang/cargo#3301 [cargo/3443]: rust-lang/cargo#3443 [cargo/3511]: rust-lang/cargo#3511 [cargo/3515]: rust-lang/cargo#3515 [cargo/3534]: rust-lang/cargo#3534 [cargo/3546]: rust-lang/cargo#3546 [cargo/3557]: rust-lang/cargo#3557 [cargo/3604]: rust-lang/cargo#3604 [RFC 1623]: https://github.com/rust-lang/rfcs/blob/master/text/1623-static.md
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The name resolution part is easy, but the typeck part contains an unexpected problem.
It turns out that
Selftype depends on bounds andwhereclauses, so we need to convert them first to determine what theSelftype is! If bounds/whereclauses can refer toSelfthen we have a cyclic dependency.This is required to support impls like this:
I'm not yet sure how to resolve this issue.
One possible solution (that feels hacky) is to make two passes over generics - first collect predicates ignoring everything involving
Self, then determineSelf, then collect predicates again without ignoring anything. (Some kind of lazy on-demand checking or something looks like a proper solution.)This patch in its current state doesn't solve the problem with
Selfin bounds, so the only observable things it does is improving error messages and supportingimpl Trait<Self> for Type {}.There's also a question about feature gating. It's non-trivial to detect "newly resolved"
Selfs to feature gate them, but it's simple to enable the new resolution behavior when the feature gate is already specified. Alternatively this can be considered a bug fix and merged without a feature gate.cc #38864
r? @nikomatsakis
cc @eddyb
Whitespace ignoring diff https://github.com/rust-lang/rust/pull/38920/files?w=1