Implement untagged unions (RFC 1444)
cc https://github.com/rust-lang/rust/issues/32836
Notes:
- The RFC doesn't talk about `#[packed]` unions, this implementation supports them, packing changes union's alignment to 1 and removes trailing padding.
- The RFC doesn't talk about dynamically sized unions, this implementation doesn't support them and rejects them during wf-checking (similarly, dynamically sized enums are not supported as well).
- The lint for drop fields in unions can't work precisely before monomorphization, so it works pessimistically - non-`Copy` generic fields are reported, types not implementing `Drop` directly, but having non-trivial drop code are reported.
```
struct S(String); // Doesn't implement `Drop`
union U<T> {
a: S, // Reported
b: T, // Reported
}
```
- https://github.com/rust-lang/rust/pull/35764 was indeed helpful and landed timely, I didn't have to implement internal drop flags for unions.
- Unions are not permitted in constant patterns, because matching on union fields is unsafe, I didn't want unsafety checker to dig into all constants to uncover this possible unsafety.
- The RFC doesn't talk about `#[derive]`, generally trait impls cannot be derived for unions, but some of them can. I implemented only `#[derive(Copy)]` so far. In theory shallow `#[derive(Clone)]` can be derived as well if all union fields are `Copy`, I left it for later though, it requires changing how `Clone` impls are generated.
- Moving union fields is implemented as per https://github.com/rust-lang/rust/issues/32836#issuecomment-242511491.
- Testing strategy: union specific behavior is tested, sometimes very basically (e.g. debuginfo), behavior common for all ADTs (e.g. something like coherence
checks) is not generally tested.
r? @eddyb
When using --enable-local-rebuild configure options, the configure
script will test rustc version. But when running it, it will not use the
libraries in the local-rust-root directory.
So use `LD_LIBRARY_PATH` environment variable to correct it.
rustc: Implement custom derive (macros 1.1)
This commit is an implementation of [RFC 1681] which adds support to the
compiler for first-class user-define custom `#[derive]` modes with a far more
stable API than plugins have today.
[RFC 1681]: https://github.com/rust-lang/rfcs/blob/master/text/1681-macros-1.1.md
The main features added by this commit are:
* A new `rustc-macro` crate-type. This crate type represents one which will
provide custom `derive` implementations and perhaps eventually flower into the
implementation of macros 2.0 as well.
* A new `rustc_macro` crate in the standard distribution. This crate will
provide the runtime interface between macro crates and the compiler. The API
here is particularly conservative right now but has quite a bit of room to
expand into any manner of APIs required by macro authors.
* The ability to load new derive modes through the `#[macro_use]` annotations on
other crates.
All support added here is gated behind the `rustc_macro` feature gate, both for
the library support (the `rustc_macro` crate) as well as the language features.
There are a few minor differences from the implementation outlined in the RFC,
such as the `rustc_macro` crate being available as a dylib and all symbols are
`dlsym`'d directly instead of having a shim compiled. These should only affect
the implementation, however, not the public interface.
This commit also ended up touching a lot of code related to `#[derive]`, making
a few notable changes:
* Recognized derive attributes are no longer desugared to `derive_Foo`. Wasn't
sure how to keep this behavior and *not* expose it to custom derive.
* Derive attributes no longer have access to unstable features by default, they
have to opt in on a granular level.
* The `derive(Copy,Clone)` optimization is now done through another "obscure
attribute" which is just intended to ferry along in the compiler that such an
optimization is possible. The `derive(PartialEq,Eq)` optimization was also
updated to do something similar.
---
One part of this PR which needs to be improved before stabilizing are the errors
and exact interfaces here. The error messages are relatively poor quality and
there are surprising spects of this such as `#[derive(PartialEq, Eq, MyTrait)]`
not working by default. The custom attributes added by the compiler end up
becoming unstable again when going through a custom impl.
Hopefully though this is enough to start allowing experimentation on crates.io!
Introduce max_by/min_by on iterators
See https://github.com/rust-lang/rfcs/issues/1722 for reference.
It seems that there is `min`, `max` (simple computation of min/max), `min_by_key`, `max_by_key` (min/max by comparing mapped values) but no `min_by` and `max_by` (min/max according to comparison function). However, e.g. on vectors or slices there is `sort`, `sort_by_key` and `sort_by`.
Fixed E0529's label and unit test
Fixes#36195 part of #35233.
This is ready for review, but will likely fail Travis due to #36138. I changed the wording of the label, so feedback on that would be appreciated.
r? @jonathandturner
test: Add a min-llvm-version directive
We've got tests which require a particular version of LLVM to run as they're
testing bug fixes. Our build system, however, supports multiple LLVM versions,
so we can't run these tests on all LLVM versions.
This adds a new `min-llvm-version` directive for tests so they can opt out of
being run on older versions of LLVM. This then namely applies that logic to the
`issue-36023.rs` test case and...
Closes#36138
Update lifetime errors to specifically note temporaries
This PR updates the error message we give in the case of a temporary value not living long enough.
Before:
<img width="497" alt="screen shot 2016-08-31 at 10 02 47 am" src="https://cloud.githubusercontent.com/assets/547158/18138551/27a06794-6f62-11e6-9ee2-bdf8bed75ca7.png">
Now:
<img width="488" alt="screen shot 2016-08-31 at 10 03 01 am" src="https://cloud.githubusercontent.com/assets/547158/18138557/2e5cf322-6f62-11e6-9047-4a78abf3d78c.png">
Specifically, it makes the following changes:
* Detects if a temporary is being used. If so, it changes the labels to mention that a temporary value specifically is in question
* Simplifies wording of the existing labels to focus on lifetimes rather than values being valid
* Changes the help to a note, since the help+span wasn't as helpful (and sometimes more confusing) than just a note.
r? @nikomatsakis
Normalize the function signature of closures
Previously we didn't normalize the function signatures used for
closures. This didn't cause a problem in most cases, but caused an ICE
in during MIR type checking.
Fixes#36139
r? @eddyb
Document try!'s error conversion behaviour
try!'s documentation currently doesn't document the error conversion behaviour of the macro. This patch extends the documentation.
Open questions:
* is it worthwhile to have seperate examples with and without wrapping behaviour? It's not immediately obvious that From<T> for T is always defined. Though this is necessary for the macro to work in any case, is this the place to expect that knowledge.
Corey Farwell
bors
Alex Crichton
Guillaume Gomez
Sébastien Marie
Cobrand
Vadim Petrochenkov
Alex Burka
Alex Burka
Jonathan Turner
Abhishek Kumar
Andrea Corradi
