For a call like `foo.bar()` where the method `bar` can't be resolved,
the compiler will search for traits that have methods with name `bar` to
give a more informative error, providing a list of possibilities.
Closes#7643.
With the addition of separate search paths to the compiler, it was intended that
applications such as Cargo could require a `--extern` flag per `extern crate`
directive in the source. The system can currently be subverted, however, due to
the `existing_match()` logic in the crate loader.
When loading crates we first attempt to match an `extern crate` directive
against all previously loaded crates to avoid reading metadata twice. This "hit
the cache if possible" step was erroneously leaking crates across the search
path boundaries, however. For example:
extern crate b;
extern crate a;
If `b` depends on `a`, then it will load crate `a` when the `extern crate b`
directive is being processed. When the compiler reaches `extern crate a` it will
use the previously loaded version no matter what. If the compiler was not
invoked with `-L crate=path/to/a`, it will still succeed.
This behavior is allowing `extern crate` declarations in Cargo without a
corresponding declaration in the manifest of a dependency, which is considered
a bug.
This commit fixes this problem by keeping track of the origin search path for a
crate. Crates loaded from the dependency search path are not candidates for
crates which are loaded from the crate search path.
With the addition of separate search paths to the compiler, it was intended that
applications such as Cargo could require a `--extern` flag per `extern crate`
directive in the source. The system can currently be subverted, however, due to
the `existing_match()` logic in the crate loader.
When loading crates we first attempt to match an `extern crate` directive
against all previously loaded crates to avoid reading metadata twice. This "hit
the cache if possible" step was erroneously leaking crates across the search
path boundaries, however. For example:
extern crate b;
extern crate a;
If `b` depends on `a`, then it will load crate `a` when the `extern crate b`
directive is being processed. When the compiler reaches `extern crate a` it will
use the previously loaded version no matter what. If the compiler was not
invoked with `-L crate=path/to/a`, it will still succeed.
This behavior is allowing `extern crate` declarations in Cargo without a
corresponding declaration in the manifest of a dependency, which is considered
a bug.
This commit fixes this problem by keeping track of the origin search path for a
crate. Crates loaded from the dependency search path are not candidates for
crates which are loaded from the crate search path.
As a result of this fix, this is a likely a breaking change for a number of
Cargo packages. If the compiler starts informing that a crate can no longer be
found, it likely means that the dependency was forgotten in your Cargo.toml.
[breaking-change]
This PR adds rules for negative implementations. It follows pretty much what the [RFC](https://github.com/rust-lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md) says with 1 main difference:
Instead of positive implementations override negative implementations, this have been implemented in a way that a negative implementation of `Trait` for `T` will overlap with a positive implementation, causing a coherence error.
@nikomatsakis r?
cc #13231
[breaking-change]
If `a.method();` can't be resolved, we first look for implemented traits
globally and suggest those. If there are no such traits found, we only
then fall back to suggesting from the unfiltered list of traits.
Currently, we build a closure that does nothing but pass its argument
through to another function, this is rather wasteful and creates lots of
unnecessary closures.
While it's unstable and will probably be replaced or "reformed" at some point, it's useful in the mean time to be able to introspect the type system when debugging, and not be limited to sized types.
Fixes#21058
...to make it slightly clearer that there's not much point in boxing a vec.
On a different note, I read the contribution guidelines (https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-request-procedure) which say I should update the copyright date for this file. But I can see that nobody else has done this so far this year, despite there being a fair number of commits.
Does that instruction need removing?
Really small correction.
This anti-example in the Closures section is supposed to fail because of a borrow, but it was failing at the type inference because of insufficient type information.
This makes it fail for the expected reason.
