Implement multidispatch and conditional dispatch. Because we do not attempt to preserve crate concatenation, this is a backwards compatible change. This is not yet fully integrated into method dispatch, so "UFCS"-style wrappers must be used to take advantage of the new features (see the run-pass tests).
cc #17307 (multidispatch)
cc #5527 (trait reform -- conditional dispatch)
Because we no longer preserve crate concatenability, this deviates slightly from what was specified in the RFC. The motivation for this change is described in [this blog post](http://smallcultfollowing.com/babysteps/blog/2014/09/30/multi-and-conditional-dispatch-in-traits/). I will post an amendment to the RFC in due course but do not anticipate great controversy on this point -- particularly as the RFCs more important features (e.g., conditional dispatch) just don't work without the change.
This change is an implementation of [RFC 69][rfc] which adds a third kind of
global to the language, `const`. This global is most similar to what the old
`static` was, and if you're unsure about what to use then you should use a
`const`.
The semantics of these three kinds of globals are:
* A `const` does not represent a memory location, but only a value. Constants
are translated as rvalues, which means that their values are directly inlined
at usage location (similar to a #define in C/C++). Constant values are, well,
constant, and can not be modified. Any "modification" is actually a
modification to a local value on the stack rather than the actual constant
itself.
Almost all values are allowed inside constants, whether they have interior
mutability or not. There are a few minor restrictions listed in the RFC, but
they should in general not come up too often.
* A `static` now always represents a memory location (unconditionally). Any
references to the same `static` are actually a reference to the same memory
location. Only values whose types ascribe to `Sync` are allowed in a `static`.
This restriction is in place because many threads may access a `static`
concurrently. Lifting this restriction (and allowing unsafe access) is a
future extension not implemented at this time.
* A `static mut` continues to always represent a memory location. All references
to a `static mut` continue to be `unsafe`.
This is a large breaking change, and many programs will need to be updated
accordingly. A summary of the breaking changes is:
* Statics may no longer be used in patterns. Statics now always represent a
memory location, which can sometimes be modified. To fix code, repurpose the
matched-on-`static` to a `const`.
static FOO: uint = 4;
match n {
FOO => { /* ... */ }
_ => { /* ... */ }
}
change this code to:
const FOO: uint = 4;
match n {
FOO => { /* ... */ }
_ => { /* ... */ }
}
* Statics may no longer refer to other statics by value. Due to statics being
able to change at runtime, allowing them to reference one another could
possibly lead to confusing semantics. If you are in this situation, use a
constant initializer instead. Note, however, that statics may reference other
statics by address, however.
* Statics may no longer be used in constant expressions, such as array lengths.
This is due to the same restrictions as listed above. Use a `const` instead.
[breaking-change]
Closes#17718
[rfc]: https://github.com/rust-lang/rfcs/pull/246
parameter list.
This breaks code like:
fn f(a: int, a: int) { ... }
fn g<T,T>(a: T) { ... }
Change this code to not use the same name for a parameter. For example:
fn f(a: int, b: int) { ... }
fn g<T,U>(a: T) { ... }
Code like this is *not* affected, since `_` is not an identifier:
fn f(_: int, _: int) { ... } // OK
Closes#17568.
r? @alexcrichton
[breaking-change]
This change is an implementation of [RFC 69][rfc] which adds a third kind of
global to the language, `const`. This global is most similar to what the old
`static` was, and if you're unsure about what to use then you should use a
`const`.
The semantics of these three kinds of globals are:
* A `const` does not represent a memory location, but only a value. Constants
are translated as rvalues, which means that their values are directly inlined
at usage location (similar to a #define in C/C++). Constant values are, well,
constant, and can not be modified. Any "modification" is actually a
modification to a local value on the stack rather than the actual constant
itself.
Almost all values are allowed inside constants, whether they have interior
mutability or not. There are a few minor restrictions listed in the RFC, but
they should in general not come up too often.
* A `static` now always represents a memory location (unconditionally). Any
references to the same `static` are actually a reference to the same memory
location. Only values whose types ascribe to `Sync` are allowed in a `static`.
This restriction is in place because many threads may access a `static`
concurrently. Lifting this restriction (and allowing unsafe access) is a
future extension not implemented at this time.
* A `static mut` continues to always represent a memory location. All references
to a `static mut` continue to be `unsafe`.
This is a large breaking change, and many programs will need to be updated
accordingly. A summary of the breaking changes is:
* Statics may no longer be used in patterns. Statics now always represent a
memory location, which can sometimes be modified. To fix code, repurpose the
matched-on-`static` to a `const`.
static FOO: uint = 4;
match n {
FOO => { /* ... */ }
_ => { /* ... */ }
}
change this code to:
const FOO: uint = 4;
match n {
FOO => { /* ... */ }
_ => { /* ... */ }
}
* Statics may no longer refer to other statics by value. Due to statics being
able to change at runtime, allowing them to reference one another could
possibly lead to confusing semantics. If you are in this situation, use a
constant initializer instead. Note, however, that statics may reference other
statics by address, however.
* Statics may no longer be used in constant expressions, such as array lengths.
This is due to the same restrictions as listed above. Use a `const` instead.
[breaking-change]
[rfc]: https://github.com/rust-lang/rfcs/pull/246
While booleans are represented as i1 in SSA values, LLVM expects them
to be stored/loaded as i8 values. Using i1 as we do now works, but
kills some optimizations, so we should switch to i8, just like we do
everywhere else.
Fixes#16959.
While booleans are represented as i1 in SSA values, LLVM expects them
to be stored/loaded as i8 values. Using i1 as we do now works, but
kills some optimizations, so we should switch to i8, just like we do
everywhere else.
Fixes#16959.
This fixes a soundness problem where `Fn` unboxed closures can mutate free variables in the environment.
The following presently builds:
```rust
#![feature(unboxed_closures, overloaded_calls)]
fn main() {
let mut x = 0u;
let _f = |&:| x = 42;
}
```
However, this is equivalent to writing the following, which borrowck rightly rejects:
```rust
struct F<'a> {
x: &'a mut uint
}
impl<'a> Fn<(),()> for F<'a> {
#[rust_call_abi_hack]
fn call(&self, _: ()) {
*self.x = 42; // error: cannot assign to data in a `&` reference
}
}
fn main() {
let mut x = 0u;
let _f = F { x: &mut x };
}
```
This problem is unique to unboxed closures; boxed closures cannot be invoked through an immutable reference and are not subject to it.
This change marks upvars of `Fn` unboxed closures as freely aliasable in mem_categorization, which causes borrowck to reject attempts to mutate or mutably borrow them.
@zwarich pointed out that even with this change, there are remaining soundness issues related to regionck (issue #17403). This region issue affects boxed closures as well.
Closes issue #17780
parameter list.
This breaks code like:
fn f(a: int, a: int) { ... }
fn g<T,T>(a: T) { ... }
Change this code to not use the same name for a parameter. For example:
fn f(a: int, b: int) { ... }
fn g<T,U>(a: T) { ... }
Code like this is *not* affected, since `_` is not an identifier:
fn f(_: int, _: int) { ... } // OK
Closes#17568.
[breaking-change]
Apart from making the build system determine the LLDB version, this PR also fixes an issue with enums in LLDB pretty printers. In order for GDB's pretty printers to know for sure if a field of some value is an enum discriminant, I had rustc mark discriminant fields with the `artificial` DWARF tag. This worked out nicely for GDB but it turns out that one can't access artificial fields from LLDB. So I changed the debuginfo representation so that enum discriminants are marked by the special field name `RUST$ENUM$DISR` instead, which works in both cases.
The PR does not activate the LLDB test suite yet.
LLDB doesn't allow for reading 'artifical' fields (fields that are generated by the compiler). So do not mark, slice fields, enum discriminants, and GcBox value fields as artificial.
This causes borrowck to correctly reject mutation or mutable borrows
of upvars in `Fn` unboxed closures since the closure environment is
aliasable.
This also tracks the responsible closure in the aliasability
information returned and uses it to give a helpful diagnostic.
Closes issue #17780
This is a quick fix that prevents an ICE by mimicing the visitor
glue for boxed closures and bare functions. Ideally, the `TyVisitor`
interface will be improved in the future to allow representing
more information about unboxed closures such as Fn/FnMut/FnOnce
status, capture mode, and captured free variable types and offsets.
Closes issue #17737
This began as an attempt to fix an ICE in borrowck (issue #17655), but the rabbit hole went pretty deep. I ended up plumbing support for capture-by-reference unboxed closures all the way into trans.
Closes issue #17655.
