This pull request implements the functionality for [RFC 873](https://github.com/rust-lang/rfcs/blob/master/text/0873-type-macros.md). This is currently just an update of @freebroccolo's branch from January, the corresponding commits are linked in each commit message.
@nikomatsakis and I had talked about updating the macro language to support a lifetime fragment specifier, and it is possible to do that work on this branch as well. If so we can (collectively) talk about it next week during the pre-RustCamp work week.
This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.
[rfc]: https://github.com/rust-lang/rfcs/pull/1184
Fixes#25022
This adapts the deriving mechanism to not repeat bounds for the same type parameter. To give an example: for the following code:
```rust
#[derive(Clone)]
pub struct FlatMap<I, U: IntoIterator, F> {
iter: I,
f: F,
frontiter: Option<U::IntoIter>,
backiter: Option<U::IntoIter>,
}
```
the latest nightly generates the following impl signature:
```rust
impl <I: ::std::clone::Clone,
U: ::std::clone::Clone + IntoIterator,
F: ::std::clone::Clone>
::std::clone::Clone for FlatMap<I, U, F> where
I: ::std::clone::Clone,
F: ::std::clone::Clone,
U::IntoIter: ::std::clone::Clone,
U::IntoIter: ::std::clone::Clone
```
With these changes, the signature changes to this:
```rust
impl <I, U: IntoIterator, F> ::std::clone::Clone for FlatMap<I, U, F> where
I: ::std::clone::Clone,
F: ::std::clone::Clone,
U::IntoIter: ::std::clone::Clone
```
(Nothing in the body of the impl changes)
Note that the second impl is more permissive, as it doesn't have a `Clone` bound on `U` at all. There was a compile-fail test that failed due to this. I don't understand why we would want the old behaviour (and nobody on IRC could tell me either), so please tell me if there is a good reason that I missed.
`LocalSource` indicated wether a let binding originated from for-loop desugaring to enable specialized error messages, but for-loop expansion has changed and this is now achieved through `MatchSource::ForLoopDesugar`.
This introduces a test for #23389 and improves the error behaviour to treat the malformed LHS as an error, not a compiler bug.
The parse phase that precedes the call to `check_lhs_nt_follows` could possibly be enhanced to police the format itself (which the old code suggests was the original intention), but I'm not sure that's any nicer than just parsing the matcher as generic rust code and then policing the specific requirements for being a macro matcher afterwards (as this does).
Fixes#23389
(Over time the stability checking has gotten more finicky; in
particular one must attach the (whole) span of the original `in PLACE
BLOCK` expression to the injected references to unstable paths, as
noted in the comments.)
call `push_compiler_expansion` during the placement-`in` expansion.
Even after expansion, the generated expressions still track depth of
such pushes (i.e. how often you have "pushed" without a corresponding
"pop"), and we add a rule that in a context with a positive
`push_unsafe!` depth, it is effectively an `unsafe` block context.
(This way, we can inject code that uses `unsafe` features, but still
contains within it a sub-expression that should inherit the outer
safety checking setting, outside of the injected code.)
This is a total hack; it not only needs a feature-gate, but probably
should be feature-gated forever (if possible).
ignore-pretty in test/run-pass/pushpop-unsafe-okay.rs
This commit expands the follow set of the `ty` and `path` macro fragments to
include the semicolon token as well. A semicolon is already allowed after these
tokens, so it's currently a little too restrictive to not have a semicolon
allowed. For example:
extern {
fn foo() -> i32; // semicolon after type
}
fn main() {
struct Foo;
Foo; // semicolon after path
}
This commit expands the follow set of the `ty` and `path` macro fragments to
include the semicolon token as well. A semicolon is already allowed after these
tokens, so it's currently a little too restrictive to not have a semicolon
allowed. For example:
extern {
fn foo() -> i32; // semicolon after type
}
fn main() {
struct Foo;
Foo; // semicolon after path
}
The common pattern `iter::repeat(elt).take(n).collect::<Vec<_>>()` is
exactly equivalent to `vec![elt; n]`, do this replacement in the whole
tree.
(Actually, vec![] is smart enough to only call clone n - 1 times, while
the former solution would call clone n times, and this fact is
virtually irrelevant in practice.)
The new code generated for deriving on enums looks something like this:
```rust
let __self0_vi = unsafe {
std::intrinsics::discriminant_value(&self) } as i32;
let __self1_vi = unsafe {
std::intrinsics::discriminant_value(&__arg1) } as i32;
let __self2_vi = unsafe {
std::intrinsics::discriminant_value(&__arg2) } as i32;
///
if __self0_vi == __self1_vi && __self0_vi == __self2_vi && ... {
match (...) {
(Variant1, Variant1, ...) => Body1
(Variant2, Variant2, ...) => Body2,
...
_ => ::core::intrinsics::unreachable()
}
}
else {
... // catch-all remainder can inspect above variant index values.
}
```
This helps massively for C-like enums since they will be compiled as a
single comparison giving observed speedups of up to 8x. For more complex
enums the speedup is more difficult to measure but it should not be
slower to generate code this way regardless.
Needed to support:
```rust
match X {
pattern if Y ...
}
for pattern in Y {}
```
IMO, this shouldn't require an RFC because it can't interfere with any future language changes (because `pattern if` and `pattern in` are already legal in rust) and can't cause any ambiguity.
This is a port of @eddyb's `const-fn` branch. I rebased it, tweaked a few things, and added tests as well as a feature gate. The set of tests is still pretty rudimentary, I'd appreciate suggestions on new tests to write. Also, a double-check that the feature-gate covers all necessary cases.
One question: currently, the feature-gate allows the *use* of const functions from stable code, just not the definition. This seems to fit our usual strategy, and implies that we might (perhaps) allow some constant functions in libstd someday, even before stabilizing const-fn, if we were willing to commit to the existence of const fns but found some details of their impl unsatisfactory.
r? @pnkfelix
