generalize impl trait to permit multiple lifetime bounds
Generalizes the region solver to support "pick constraints". These have the form:
```
pick R0 from [R1..Rn]
```
where `R1..Rn` are called the "option regions". The idea is that `R0` must be equal to *some* region in the set `R1..Rn`. These constraints are then used to handle cases like this:
```rust
fn foo<'a, 'b>(...) -> impl Trait<'a, 'b> { .. }
```
The problem here is that every region R in the hidden type must be equal to *either* `'a` *or* `'b` (or `'static`) -- in the past, the only kinds of constraints we had were outlives constraints, and since `'a` and `'b` are unrelated, there was no outlives constraint we could issue that would enforce that (`R: 'a` and `R: 'b` are both too strict, for example). But now we can issue a pick constraint: `pick R from ['a, 'b]`.
In general, solving pick constraints is tricky. We integrate them into the solver as follows. In general, during the propagation phase, we are monotonically growing a set of inference regions. To handle a case like `pick R from [O...]`, where `O...` represents the option regions, we do the following:
- Look for all the *lower bounds* of the region R -- that is, every region LB such that `R: LB` must hold.
- Look for all the *upper bounds* of the region R -- that is, every region UB such that `UB: R` must hold.
- Let the *viable options* be each option region O such that `UB: O` and `O: LB` for each UB, LB bound.
- Find the *minimal viable option* M, where `O: M` holds for every option region O.
If there is such a *minimal viable option*, then we make `R: M`. (This may in turn influence other bits of inference.) If there is no minimal viable option, either because all options were eliminated or because none of the remaining options are minimal, we do nothing. Ultimately, if the pick constraint is not satisfied, an error is reported.
For this logic, we currently require that the option regions O are always lifetime parameters. To determine the bounds, we walk the various outlives edges that were otherwise introduced.
r? @matthewjasper
cc @cramertj
Fixes#56238
TODO:
- [ ] Error messages include region variable info sometimes, how to fix?
- [ ] Tests for bare `existential type` and other impl Trait usage
Stabilize support for Profile-guided Optimization
This PR makes profile-guided optimization available via the `-C profile-generate` / `-C profile-use` pair of commandline flags and adds end-user documentation for the feature to the [rustc book](https://doc.rust-lang.org/rustc/). The PR thus ticks the last two remaining checkboxes of the [stabilization tracking issue](https://github.com/rust-lang/rust/issues/59913).
From the tracking issue:
> Profile-guided optimization (PGO) is a common optimization technique for ahead-of-time compilers. It works by collecting data about a program's typical execution (e.g. probability of branches taken, typical runtime values of variables, etc) and then uses this information during program optimization for things like inlining decisions, machine code layout, or indirect call promotion.
If you are curious about how this can be used, there is a rendered version of the documentation this PR adds available [here](
https://github.com/michaelwoerister/rust/blob/stabilize-pgo/src/doc/rustc/src/profile-guided-optimization.md).
r? @alexcrichton
cc @rust-lang/compiler
Stabilize `type_alias_enum_variants` in Rust 1.37.0
Stabilize `#![feature(type_alias_enum_variants)]` which allows type-relative resolution with highest priority to `enum` variants in both expression and pattern contexts. For example, you may now write:
```rust
enum Option<T> {
None,
Some(T),
}
type OptAlias<T> = Option<T>;
fn work_on_alias(x: Option<u8>) -> u8 {
match x {
OptAlias::Some(y) => y + 1,
OptAlias::None => 0,
}
}
```
Closes https://github.com/rust-lang/rfcs/issues/2218
Closes https://github.com/rust-lang/rust/issues/52118
r? @petrochenkov
Update books
Update nomicon, reference, book, rust-by-example, rustc-guide
## nomicon
2 commits in c656171b749b7307f21371dd0d3278efee5573b8..341c221116a8b9f1010cf1eece952b80c5ec7f54
2019-04-25 15:31:26 -0400 to 2019-06-19 09:08:47 -0700
- Fix some links.
- cleanup the intro, and clarify how it relates to the reference (rust-lang-nursery/nomicon#140)
## reference
2 commits in 08ae27a4921ca53967656a7391c82f6c0ddd1ccc..7a5aab5fd50d6290679beb4cf42fa5f46ed22aec
2019-06-17 11:24:13 -0700 to 2019-06-20 17:38:52 +0200
- Update for cfg on generic parameter. (rust-lang-nursery/reference#624)
- Link to "const functions" section from constant expressions list (rust-lang-nursery/reference#623)
## book
2 commits in 9aacfcc4c5b102c8cda195932addefd32fe955d2..6c0d83499c8e77e06a71d28c5e1adccec278d4f3
2019-06-16 21:27:26 -0400 to 2019-06-23 20:25:30 -0400
- fancy quotes
- Edits made in copyedit
## rust-by-example
2 commits in b27472962986e85c94f4183b1a6d2207660d3ed6..62b3ff2cb44dd8b648c3ef2a9347c3706d148014
2019-06-17 15:52:07 -0300 to 2019-06-24 09:17:21 -0300
- A couple of fixes for the `Box, stack and heap` chapter. (rust-lang/rust-by-example#1206)
- [typo] Note, that it is -> Note that, it is (rust-lang/rust-by-example#1207)
## rustc-guide
38 commits in f55e97c145cf37fd664db2e0e2f2d05df328bf4f..abf512fc9cc969dcbea69aa15b44586bbeb13c2d
2019-06-15 17:29:12 -0500 to 2019-06-26 11:05:58 -0500
- fix long line
- add `point` to the glossary and link a use of it
- fix indentation
- Update src/borrow_check/region_inference/placeholders_and_universes.md
- Update src/borrow_check/region_inference/placeholders_and_universes.md
- Update src/borrow_check/region_inference/placeholders_and_universes.md
- Update src/borrow_check/region_inference/member_constraints.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/member_constraints.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/member_constraints.md
- Update src/borrow_check/region_inference/member_constraints.md
- Update src/borrow_check/region_inference/lifetime_parameters.md
- Update src/borrow_check/region_inference/member_constraints.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- Update src/borrow_check/region_inference/lifetime_parameters.md
- Update src/borrow_check/region_inference/lifetime_parameters.md
- Update src/borrow_check/region_inference/lifetime_parameters.md
- Update src/borrow_check/region_inference/constraint_propagation.md
- adjust overview slightly
- describe region inference and member constraints in some detail
- start filling out the constraint propagation chapter in more detail
- break out parts of the region inference chapter into sub-chapters
- fix typo
- avoid ftp links
- fix broken links
- add bibligraphy appendix
- Update to mdbook-linkcheck 0.3.0
- Update mdbook
- Change stage0 cfg_attr to bootstrap
- fix compiler-team
- Added Rustc Debugger Support Chapter
Stabilize #![feature(repr_align_enum)] in Rust 1.37.0
On an `enum` item, you may now write:
```rust
#[repr(align(X))]
enum Foo {
// ...
}
```
This has equivalent effects to first defining:
```rust
#[repr(align(X))]
struct AlignX<T>(T);
```
and then using `AlignX<Foo>` in `Foo`'s stead.
r? @nagisa
Update books
## reference
2 commits in 862b669c395822bb0938781d74f860e5762ad4fb..f8ae436d936f6f4891d3c1bbb1af5865eb8aeadb
2019-05-04 23:41:35 -0700 to 2019-05-31 14:59:12 +0200
- Document that literals with any suffixes are valid as tokens (rust-lang-nursery/reference#612)
- Fix example code of derive macro (rust-lang-nursery/reference#611)
## book
2 commits in 29fe982990e43b9367be0ff47abc82fb2123fd03..62a8c6f25fbd981c80a046f3b04be9684749af3b
2019-05-15 17:48:40 -0400 to 2019-05-28 15:48:23 -0400
- Remove snapshots checked in layout
- Remove snapshots that I've approved in layout
## rust-by-example
5 commits in 811c697b232c611ed754d279ed20643a0c4096f6..18566f4dedc3ef5bf61f5f85685d5966db99cc11
2019-04-28 18:56:42 -0300 to 2019-05-30 19:23:24 -0300
- Fixed wording in the `Seconds` struct description. (rust-lang/rust-by-example#1195)
- Fix usage of the word "elision" (rust-lang/rust-by-example#1191)
- Reword "Flow Control" to "Flow of Control" (rust-lang/rust-by-example#1190)
- Copy edits to chapter 1 (rust-lang/rust-by-example#1189)
- Fix typo in a mod/visibility.md (rust-lang/rust-by-example#1188)
## rustc-guide
9 commits in 3cb727b62b953d59b4360d39aa68b6dc8f157655..3ac9cfc9c9ab2e366feebf18718112737f572352
2019-05-07 09:53:32 -0500 to 2019-06-02 19:36:58 -0500
- Update information about debuginfo configuration
- fix long line
- Fixed misspelling
- Add more info subsection with links to forge and rustc api docs (rust-lang/rustc-guide#324)
- Renamed the file and title of the diagnostics chapter.
- Added rustc phases diagram and explanation
- Mention running tests for subdirectories
- Fixed links broken by merging chalks rules and solve
- Add documentation about profile-guided optimization.
## embedded-book
1 commits in 9858872bd1b7dbba5ec27dc30d34eba00acd7ef9..f0c75b75f9c18537b78f5d17c1015247e9a49c86
2019-05-02 18:56:54 +0000 to 2019-06-03 10:49:02 +0000
- Qemu md changes (rust-embedded/book#193)
Migrate some books to mdbook version 0.2
There are 3 books still using old version but they need more effort so I hope to do them in subsequent PR if I find the time.
implicit `Option`-returning doctests
This distinguishes `Option` and `Result`-returning doctests with implicit `main` method, where the former tests must end with `Some(())`.
Open question: Does this need a feature gate?
r? @GuillaumeGomez
lint: convert incoherent_fundamental_impls into hard error
*Summary for affected authors:* If your crate depends on one of the following crates, please upgrade to a newer version:
- gtk-rs: upgrade to at least 0.4
- rusqlite: upgrade to at least 0.14
- nalgebra: upgrade to at least 0.15, or the last patch version of 0.14
- spade: upgrade or refresh the Cargo.lock file to use version 1.7
- imageproc: upgrade to at least 0.16 (newer versions no longer use nalgebra)
implement #46205
r? @nikomatsakis
Update books
## nomicon
1 commits in fb29b147be4d9a1f8e24aba753a7e1de537abf61..c656171b749b7307f21371dd0d3278efee5573b8
2019-04-22 19:10:29 -0400 to 2019-04-25 15:31:26 -0400
- Lifetimes: Updates to incorporate NLL (rust-lang-nursery/nomicon#101)
## reference
5 commits in 2a2de9ce095979978ad7b582daecf94e4070b916..862b669c395822bb0938781d74f860e5762ad4fb
2019-04-22 10:25:52 -0700 to 2019-05-04 23:41:35 -0700
- Typo (rust-lang-nursery/reference#606)
- Added missing ? to Generics from InherentImpl and TraitImpl (rust-lang-nursery/reference#604)
- Add missing ( to ExternalFunctionItem (rust-lang-nursery/reference#603)
- Remove unneeded | from AssignmentExpression (rust-lang-nursery/reference#601)
- Remove unneeded ( from TypePathSegment (rust-lang-nursery/reference#602)
## book
6 commits in db919bc6bb9071566e9c4f05053672133eaac33e..29fe982990e43b9367be0ff47abc82fb2123fd03
2019-04-15 20:11:03 -0400 to 2019-05-15 17:48:40 -0400
- Ignore a non-compiling test listing and add code to fix a test listing
- Remove nostarch snapshots I've checked in layout
- Reword error messages to maybe not need to wrap lines in print
- This example doesn't compile but wasn't marked as such
- Update install instructions for VS 2019 (rust-lang/book#1923)
- Switch IRC to Discord
## rust-by-example
9 commits in 1ff0f8e018838a710ebc0cc1a7bf74ebe73ad9f1..811c697b232c611ed754d279ed20643a0c4096f6
2019-04-15 08:15:32 -0300 to 2019-04-28 18:56:42 -0300
- Fix typo in dsl.md (rust-lang/rust-by-example#1187)
- File read lines (rust-lang/rust-by-example#1186)
- For https://github.com/rust-lang/rust-by-example/issues/1184closesrust-lang/rust-by-example#1184 (rust-lang/rust-by-example#1185)
- Link to Reference for macro_rules designators (rust-lang/rust-by-example#1182)
- Improve section Meta/Docs (rust-lang/rust-by-example#1183)
- Small improvements to various files (rust-lang/rust-by-example#1173)
- 19.2 Vectors Error in Code Example (rust-lang/rust-by-example#1178)
- For https://github.com/rust-lang/rust-by-example/issues/1175 (rust-lang/rust-by-example#1176)
- For https://github.com/rust-lang/rust-by-example/issues/1179 (rust-lang/rust-by-example#1180)
## rustc-guide
12 commits in 99e1b1d53656be08654df399fc200584aebb50e4..3cb727b62b953d59b4360d39aa68b6dc8f157655
2019-04-20 09:57:54 -0500 to 2019-05-07 09:53:32 -0500
- Fix typo, 'which' repeated twice
- [canonicalization] fix result canonicalization example (rust-lang/rustc-guide#304)
- Rename to RUSTC_LOG
- Added mention of universal ctags
- Fix link in walkthrough
- Remove IRC from discussion chats
- Bring the updating LLVM guide up to date
- use nightly rust for ci
- Fixed broken chalk links
- Add documentation for two-phase borrows
- Explain new powers of the `treat-err-as-bug` flag
- Update lowering-module test case
## edition-guide
3 commits in c413d42a207bd082f801ec0137c31b71e4bfed4c..581c6cccfaf995394ea9dcac362dc8e731c18558
2019-04-22 01:14:56 +0200 to 2019-05-06 12:47:44 -0700
- Fix typo in controlling-panics-with-std-panic.md (rust-lang-nursery/edition-guide#158)
- Fix links for book editions. (rust-lang-nursery/edition-guide#149)
- Update now that NLL is enabled in 2015. (rust-lang-nursery/edition-guide#157)
## embedded-book
3 commits in de3d55f521e657863df45260ebbca1b10527f662..9858872bd1b7dbba5ec27dc30d34eba00acd7ef9
2019-04-22 12:58:28 +0000 to 2019-05-02 18:56:54 +0000
- Update linux.md (rust-embedded/book#167)
- Clarify list of available targets for installation (rust-embedded/book#165)
- minor grammar fix (rust-embedded/book#188)
Document the `html_root_url` doc attribute value.
I'm not sure if this was intentionally not documented, but I think it would be good to include. This was added in #9691. `--extern-html-root-url` is unstable, but I don't think it hurts to mention it.
