O(log n) lookup of associated items by name
Resolves#68957, in which compile time is quadratic in the number of associated items. This PR makes name lookup use binary search instead of a linear scan to improve its asymptotic performance. As a result, the pathological case from that issue now runs in 8 seconds on my local machine, as opposed to many minutes on the current stable.
Currently, method resolution must do a linear scan through all associated items of a type to find one with a certain name. This PR changes the result of the `associated_items` query to a data structure that preserves the definition order of associated items (which is used, e.g., for the layout of trait object vtables) while adding an index of those items sorted by (unhygienic) name. When doing name lookup, we first find all items with the same `Symbol` using binary search, then run hygienic comparison to find the one we are looking for. Ideally, this would be implemented using an insertion-order preserving, hash-based multi-map, but one is not readily available.
Someone who is more familiar with identifier hygiene could probably make this better by auditing the uses of the `AssociatedItems` interface. My goal was to preserve the current behavior exactly, even if it seemed strange (I left at least one FIXME to this effect). For example, some places use comparison with `ident.modern()` and some places use `tcx.hygienic_eq` which requires the `DefId` of the containing `impl`. I don't know whether those approaches are equivalent or which one should be preferred.
Rollup of 5 pull requests
Successful merges:
- #68877 (On mismatched argument count point at arguments)
- #69185 (Unify and improve const-prop lints)
- #69305 (Tweak binding lifetime suggestion text)
- #69311 (Clean up E0321 and E0322)
- #69317 (Fix broken link to the rustc guide)
Failed merges:
r? @ghost
Tweak binding lifetime suggestion text
We already have a structured suggestion, but the wording made it seem like that wasn't the case.
Fix#65286. r? @varkor
Unify and improve const-prop lints
Add a single helper method for all lints emitted by const-prop, and make that lint different from the CTFE `const_err` lint. Also consistently check overflow on *arithmetic*, not on the assertion, to make behavior the same for debug and release builds.
See [this summary comment](https://github.com/rust-lang/rust/pull/69185#issuecomment-587924754) for details and the latest status.
In terms of lint formatting, I went for what seems to be the better style: have a general message above the code, and then a specific message at the span:
```
error: this arithmetic operation will overflow
--> $DIR/const-err2.rs:21:18
|
LL | let a_i128 = -std::i128::MIN;
| ^^^^^^^^^^^^^^^ attempt to negate with overflow
```
We could also just have the specific message above and no text at the span if that is preferred.
I also converted some of the existing tests to use compiletest revisions, so that the same test can check a bunch of different compile flags.
Fixes https://github.com/rust-lang/rust/issues/69020.
Helps with https://github.com/rust-lang/rust/issues/69021: debug/release are now consistent, but the assoc-const test in that issue still fails (there is a FIXME in the PR for this). The reason seems to be that const-prop notices the assoc const in `T::N << 42` and does not even bother calling `const_prop` on that operation.
Has no effect on https://github.com/rust-lang/rust/issues/61821; the duplication there has entirely different reasons.
#69148 has a proper fix, but it is too big to backport.
This change avoids the ICE by actually emitting an appropriate error. The
output will be duplicated in some cases, but that's better than the
avoidable ICE.
Fix race condition when allocating source files in SourceMap
This makes allocating address space in the source map an atomic operation. `rustc` does not currently do this in parallel, so this bug can't trigger, but parsing files in parallel could trigger it, and that is something we want to do.
Fixes https://github.com/rust-lang/rust/issues/69261.
r? @wesleywiser
Make integer exponentiation methods unstably const
cc #53718
This makes the following inherent methods on integer primitives into unstable `const fn`:
- `pow`
- `checked_pow`
- `wrapping_pow`
- `overflowing_pow`
- `saturating_pow`
- `next_power_of_two`
- `checked_next_power_of_two`
- `wrapping_next_power_of_two`
Only two changes were made to the implementation of these methods. First, I had to switch from the `?` operator, which is not yet implemented in a const context, to a `try_opt` macro. Second, `next_power_of_two` was using `ops::Add::add` (see the first commit) to "get overflow checks", so I switched to `#[rustc_inherit_overflow_checks]`. I'm not quite sure why the attribute wasn't used in the first place.
Stabilize Once::is_completed
Closes#54890
This function has been around for some time. I haven't seen anyone raise any objections to it. I've personally found it useful myself. It would be nice to finally stabilize it and
Add LinkedList::remove()
LinkedList::remove() removes the element at the specified index and returns it.
I added this because I think having a remove function would be useful to have, and similar functions are in other containers, like Vec and HashMap.
I'm not sure if adding a feature like this requires an RFC or not, so I'm sorry if this PR is premature.
Allow trait methods to be called on concrete types in a const context
This partially implements [RFC 2632](https://github.com/rust-lang/rfcs/pull/2632) by const-checking methods inside an `impl const` block and allowing those methods to be called on concrete types. Calling trait methods on type parameters in a const context is not yet allowed. Implementing this will require much more work. Since we are only concerned with methods on concrete types, we are able to take advantage of the machinery in `Instance::resolve`, which is doing most of the work.
This also propagates `#[rustc_const_unstable]` from parent items to child items, making that attribute behave like `#[stable]` and `#[unstable]` do. This allows trait methods to be marked as unstably const.
cc #67792#57563
cc @rust-lang/wg-const-eval
r? @oli-obk
Change FromStr for String to use Infallible directly
Fixes the confusing documentation on `ParseError` by making it irrelevant.
It might be fine to mark it as depreciated right now too - I can't imagine much code uses `ParseError` directly.
Before this change, `get_size_and_align()` calls `get_fn_alloc()` *a
lot* in CTFE heavy code. This previously returned an `Error` which would
check if `RUSTC_CTFE_BACKTRACE` was set on construction. Doing this
turned out to be a performance hotspot as @nnethercote discovered in
#68792.
This is an alternate take on that PR which resolves the performance
issue by generating *many* fewer errors. Previously, `ctfe-stress-4`
would generate over 5,000,000 errors each of which would check for the
presence of the environment variable. With these changes, that number is
reduced to 30.
Reword OpenOptions::{create, create_new} doc.
Closes#69254.
Currently, the doc comment for `fs::OpenOptions::create` doesn't mention its behaviour when opening an existing file, and `fs::OpenOptions::create_new`'s doc comment is worded in a way that doesn't make it clear that it actually _fails_ if the file already exists, not overwrite the existing file with a new one.
This PR addresses addresses this by rewording the doc comments to be more explicit.
r? @GuillaumeGomez
Remove special case for `simd_shuffle` arg promotion
After rust-lang/stdarch#825, these intrinsics are now defined with `#[rustc_args_required_const(2)]`, so the special-case is no longer necessary.
Add shared script for linkchecking books.
This adds a script that can be used on each book's CI to ensure they don't break local links.
I've been running something similar on the reference CI. The intent here is to add this to all the external books' CI scripts. This will help avoid dealing with broken links when updating submodules on rust-lang/rust.
