Implement destructuring assignment for tuples
This is the first step towards implementing destructuring assignment (RFC: https://github.com/rust-lang/rfcs/pull/2909, tracking issue: #71126). This PR is the first part of #71156, which was split up to allow for easier review.
Quick summary: This change allows destructuring the LHS of an assignment if it's a (possibly nested) tuple.
It is implemented via a desugaring (AST -> HIR lowering) as follows:
```rust
(a,b) = (1,2)
```
... becomes ...
```rust
{
let (lhs0,lhs1) = (1,2);
a = lhs0;
b = lhs1;
}
```
Thanks to `@varkor` who helped with the implementation, particularly around default binding modes.
r? `@petrochenkov`
The main change is that `UnstableOptions::from_environment` now requires
an (optional) crate name. If the crate name is unknown (`None`), then the new feature is not available and you still have to use `RUSTC_BOOTSTRAP=1`. In practice this means the feature is only available for `--crate-name`, not for `#![crate_name]`; I'm interested in supporting the second but I'm not sure how.
Other major changes:
- Added `Session::is_nightly_build()`, which uses the `crate_name` of
the session
- Added `nightly_options::match_is_nightly_build`, a convenience method
for looking up `--crate-name` from CLI arguments.
`Session::is_nightly_build()`should be preferred where possible, since
it will take into account `#![crate_name]` (I think).
- Added `unstable_features` to `rustdoc::RenderOptions`
There is a user-facing change here: things like `RUSTC_BOOTSTRAP=0` no
longer active nightly features. In practice this shouldn't be a big
deal, since `RUSTC_BOOTSTRAP` is the opposite of stable and everyone
uses `RUSTC_BOOTSTRAP=1` anyway.
- Add tests
Check against `Cheat`, not whether nightly features are allowed.
Nightly features are always allowed on the nightly channel.
- Only call `is_nightly_build()` once within a function
- Use booleans consistently for rustc_incremental
Sessions can't be passed through threads, so `read_file` couldn't take a
session. To be consistent, also take a boolean in `write_file_header`.
Fix unreachable sub-branch detection in or-patterns
The previous implementation was too eager to avoid unnecessary "unreachable pattern" warnings. I feel more confident about this implementation than I felt about the previous one.
Fixes https://github.com/rust-lang/rust/issues/76836.
``@rustbot`` modify labels: +A-exhaustiveness-checking
reverse binding order in matches to allow the subbinding of copyable fields in bindings after @
Fixes#69971
### TODO
- [x] Regression tests
r? `@oli-obk`
Fix#78549
Before #78430, this worked because `specialize_constructor` didn't actually care too much which constructor was passed to it unless needed. That PR however handles `&str` as a special case, and I did not anticipate patterns for the `&str` type other than string literals.
I am not very confident there are not other similar oversights left, but hopefully only `&str` was different enough to break my assumptions.
Fixes https://github.com/rust-lang/rust/issues/78549
Before #78430, string literals worked because `specialize_constructor`
didn't actually care too much which constructor was passed to it unless
needed. Since then, string literals are special cased and a bit hacky. I
did not anticipate patterns for the `&str` type other than string
literals, hence this bug. This makes string literals less hacky.
Clarify main code paths in exhaustiveness checking
This PR massively clarifies the main code paths of exhaustiveness checking, by using the `Constructor` enum to a fuller extent. I've been itching to write it for more than a year, but the complexity of matching consts had prevented me. Behold a massive simplification :D.
This in particular removes a fair amount of duplication between various parts, localizes code into methods of relevant types when applicable, makes some implicit assumptions explicit, and overall improves legibility a lot (or so I hope). Additionally, after my changes undoing #76918 turned out to be a noticeable perf gain.
As usual I tried my best to make the commits self-contained and easy to follow. I've also tried to keep the code well-commented, but I tend to forget how complex this file is; I'm happy to clarify things as needed.
My measurements show good perf improvements on the two match-heavy benchmarks (-18.0% on `unicode_normalization-check`! :D); I'd like a perf run to check the overall impact.
r? `@varkor`
`@rustbot` modify labels: +A-exhaustiveness-checking
The test change is because we used to treat `&str` like other `&T`s, ie
as having a single constructor. That's not quite true though since we
consider `&str` constants as atomic instead of refs to `str` constants.
Also removes the ugly caching that was introduced in #76918. It was
bolted on without deeper knowledge of the workings of the algorithm.
This commit manages to be more performant without any of the complexity.
It should be better on representative workloads too.
rustc_mir: track inlined callees in SourceScopeData.
We now record which MIR scopes are the roots of *other* (inlined) functions's scope trees, which allows us to generate the correct debuginfo in codegen, similar to what LLVM inlining generates.
This PR makes the `ui` test `backtrace-debuginfo` pass, if the MIR inliner is turned on by default.
Also, `#[track_caller]` is now correct in the face of MIR inlining (cc `@anp).`
Fixes#76997.
r? `@rust-lang/wg-mir-opt`
Cleanup constant matching in exhaustiveness checking
This supercedes https://github.com/rust-lang/rust/pull/77390. I made the `Opaque` constructor work.
I have opened two issues https://github.com/rust-lang/rust/issues/78071 and https://github.com/rust-lang/rust/issues/78057 from the discussion we had on the previous PR. They are not regressions nor directly related to the current PR so I thought we'd deal with them separately.
I left a FIXME somewhere because I didn't know how to compare string constants for equality. There might even be some unicode things that need to happen there. In the meantime I preserved previous behavior.
EDIT: I accidentally fixed#78071
change the order of type arguments on ControlFlow
This allows ControlFlow<BreakType> which is much more ergonomic for common iterator combinator use cases.
Addresses one component of #75744
Clean up and improve some docs
* compiler docs
* Don't format list as part of a code block
* Clean up some other formatting
* rustdoc book
* Update CommonMark spec version to latest (0.28 -> 0.29)
* Clean up some various wording and formatting
* compiler docs
* Don't format list as part of a code block
* Clean up some other formatting
* rustdoc book
* Update CommonMark spec version to latest (0.28 -> 0.29)
* Clean up some various wording and formatting
Stabilize move_ref_pattern
# Implementation
- Initially the rule was added in the run-up to 1.0. The AST-based borrow checker was having difficulty correctly enforcing match expressions that combined ref and move bindings, and so it was decided to simplify forbid the combination out right.
- The move to MIR-based borrow checking made it possible to enforce the rules in a finer-grained level, but we kept the rule in place in an effort to be conservative in our changes.
- In #68376, @Centril lifted the restriction but required a feature-gate.
- This PR removes the feature-gate.
Tracking issue: #68354.
# Description
This PR is to stabilize the feature `move_ref_pattern`, which allows patterns
containing both `by-ref` and `by-move` bindings at the same time.
For example: `Foo(ref x, y)`, where `x` is `by-ref`,
and `y` is `by-move`.
The rules of moving a variable also apply here when moving *part* of a variable,
such as it can't be referenced or moved before.
If this pattern is used, it would result in *partial move*, which means that
part of the variable is moved. The variable that was partially moved from
cannot be used as a whole in this case, only the parts that are still
not moved can be used.
## Documentation
- The reference (rust-lang/reference#881)
- Rust by example (rust-lang/rust-by-example#1377)
## Tests
There are many tests, but I think one of the comperhensive ones:
- [borrowck-move-ref-pattern-pass.rs](85fbf49ce0/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern-pass.rs)
- [borrowck-move-ref-pattern.rs](85fbf49ce0/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.rs)
# Examples
```rust
#[derive(PartialEq, Eq)]
struct Finished {}
#[derive(PartialEq, Eq)]
struct Processing {
status: ProcessStatus,
}
#[derive(PartialEq, Eq)]
enum ProcessStatus {
One,
Two,
Three,
}
#[derive(PartialEq, Eq)]
enum Status {
Finished(Finished),
Processing(Processing),
}
fn check_result(_url: &str) -> Status {
// fetch status from some server
Status::Processing(Processing {
status: ProcessStatus::One,
})
}
fn wait_for_result(url: &str) -> Finished {
let mut previous_status = None;
loop {
match check_result(url) {
Status::Finished(f) => return f,
Status::Processing(p) => {
match (&mut previous_status, p.status) {
(None, status) => previous_status = Some(status), // first status
(Some(previous), status) if *previous == status => {} // no change, ignore
(Some(previous), status) => { // Now it can be used
// new status
*previous = status;
}
}
}
}
}
}
```
Before, we would have used:
```rust
match (&previous_status, p.status) {
(Some(previous), status) if *previous == status => {} // no change, ignore
(_, status) => {
// new status
previous_status = Some(status);
}
}
```
Demonstrating *partial move*
```rust
fn main() {
#[derive(Debug)]
struct Person {
name: String,
age: u8,
}
let person = Person {
name: String::from("Alice"),
age: 20,
};
// `name` is moved out of person, but `age` is referenced
let Person { name, ref age } = person;
println!("The person's age is {}", age);
println!("The person's name is {}", name);
// Error! borrow of partially moved value: `person` partial move occurs
//println!("The person struct is {:?}", person);
// `person` cannot be used but `person.age` can be used as it is not moved
println!("The person's age from person struct is {}", person.age);
}
```
Fix LitKind's byte buffer to use refcounted slice
While working on adding a new lint for clippy (see https://github.com/rust-lang/rust-clippy/pull/6044) for avoiding shared ownership of "mutable buffer" types (such as using `Rc<Vec<T>>` instead of `Rc<[T]>`), I noticed a type exported from rustc_ast and used by clippy gets caught by the lint. This PR fixes the exported type.
This PR includes the actual change to clippy too, but I will open a PR directly against clippy for that part (although it will currently fail to build there).
Replace `(Body, DefId)` with `Body` where possible
Follow-up to #77430.
I `grep`-ed for parameter lists in which a `Body` appeared within a few lines of a `DefId`, so it's possible that I missed some cases, but this should be pretty complete. Most of these changes were mechanical, but there's a few places where I started calling things "caller" and "callee" when multiple `DefId`s were in-scope at once. Also, we should probably have a helper function on `Body` that returns a `LocalDefId`. I can do that in this PR or in a follow-up.
There's a cleaner way of doing this, but it involves passing
`WithOptConstParam` around in more places. We're going to try to explore
different approaches before committing to that.
Previously, this method called the more general `pat_constructor`
function, which can return other pattern variants besides `IntRange`.
Then it throws away any non-`IntRange` variants. Specialize it so work
is only done when it could result in an `IntRange`.
Add fast path for match checking
This adds a fast path that would reduce the complexity to linear on matches consisting of only variant patterns (i.e. enum matches). (Also see: #7462) Unfortunately, I was too lazy to add a similar fast path for constants (mostly for integer matches), ideally that could be added another day.
TBH, I'm not confident with the performance claims due to the fact that enums tends to be small and FxHashMap could add a lot of overhead.
r? `@Mark-Simulacrum`
needs perf
Fixes#73268
When a deref coercion occurs, we may end up with a move error if the
base value has been partially moved out of. However, we do not indicate
anywhere that a deref coercion is occuring, resulting in an error
message with a confusing span.
This PR adds an explicit note to move errors when a deref coercion is
involved. We mention the name of the type that the deref-coercion
resolved to, as well as the `Deref::Target` associated type being used.
Add CONST_ITEM_MUTATION lint
Fixes#74053Fixes#55721
This PR adds a new lint `CONST_ITEM_MUTATION`.
Given an item `const FOO: SomeType = ..`, this lint fires on:
* Attempting to write directly to a field (`FOO.field = some_val`) or
array entry (`FOO.array_field[0] = val`)
* Taking a mutable reference to the `const` item (`&mut FOO`), including
through an autoderef `FOO.some_mut_self_method()`
The lint message explains that since each use of a constant creates a
new temporary, the original `const` item will not be modified.
Fixes#74053Fixes#55721
This PR adds a new lint `CONST_ITEM_MUTATION`.
Given an item `const FOO: SomeType = ..`, this lint fires on:
* Attempting to write directly to a field (`FOO.field = some_val`) or
array entry (`FOO.array_field[0] = val`)
* Taking a mutable reference to the `const` item (`&mut FOO`), including
through an autoderef `FOO.some_mut_self_method()`
The lint message explains that since each use of a constant creates a
new temporary, the original `const` item will not be modified.
Use ops::ControlFlow in rustc_data_structures::graph::iterate
Since I only know about this because you mentioned it,
r? @ecstatic-morse
If we're not supposed to use new `core` things in compiler for a while then feel free to close, but it felt reasonable to merge the two types since they're the same, and it might be convenient for people to use `?` in their traversal code.
(This doesn't do the type parameter swap; NoraCodes has signed up to do that one.)
If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.
This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.
This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.
On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.
This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.
