align_offset, align_to: no longer allow implementations to spuriously fail to align
For a long time, we have allowed `align_offset` to fail to compute a properly aligned offset, and `align_to` to return a smaller-than-maximal "middle slice". This was done to cover the implementation of `align_offset` in const-eval and Miri. See https://github.com/rust-lang/rust/issues/62420 for more background. For about the same amount of time, this has caused confusion and surprise, where people didn't realize they have to write their code to be defensive against `align_offset` failures.
Another way to put this is: the specification is effectively non-deterministic, and non-determinism is hard to test for -- in particular if the implementation everyone uses to test always produces the same reliable result, and nobody expects it to be non-deterministic to begin with.
With https://github.com/rust-lang/rust/pull/117840, Miri has stopped making use of this liberty in the spec; it now always behaves like rustc. That only leaves const-eval as potential motivation for this behavior. I do not think this is sufficient motivation. Currently, none of the relevant functions are stably const: `align_offset` is unstably const, `align_to` is not const at all. I propose that if we ever want to make these const-stable, we just accept the fact that they can behave differently at compile-time vs at run-time. This is not the end of the world, and it seems to be much less surprising to programmers than unexpected non-determinism. (Related: https://github.com/rust-lang/rfcs/pull/3352.)
`@thomcc` has repeatedly made it clear that they strongly dislike the non-determinism in align_offset, so I expect they will support this. `@oli-obk,` what do you think? Also, whom else should we involve? The primary team responsible is clearly libs-api, so I will nominate this for them. However, allowing const-evaluated code to behave different from run-time code is t-lang territory. The thing is, this is not stabilizing anything t-lang-worthy immediately, but it still does make a decision we will be bound to: if we accept this change, then
- either `align_offset`/`align_to` can never be called in const fn,
- or we allow compile-time behavior to differ from run-time behavior.
So I will nominate for t-lang as well, with the question being: are you okay with accepting either of these outcomes (without committing to which one, just accepting that it has to be one of them)? This closes the door to "have `align_offset` and `align_to` at compile-time and also always have compile-time behavior match run-time behavior".
Closes https://github.com/rust-lang/rust/issues/62420
This commit adds a `runner` field configuration to `config.toml` for
specifying a wrapper executable when executing binaries for a target.
This is pulled out of #122036 where a WebAssembly runtime is used, for
example, to execute tests for `wasm32-wasip1`.
The name "runner" here is chosen to match Cargo's `CARGO_*_RUNNER`
configuration, and to make things a bit more consistent this
additionally renames compiletest's `--runtool` argument to `--runner`.
Merge `collect_mod_item_types` query into `check_well_formed`
follow-up to https://github.com/rust-lang/rust/pull/121154
this removes more potential parallel-compiler bottlenecks and moves diagnostics for the same items next to each other, instead of grouping diagnostics by analysis kind
Remove unncessary check for macro call
Since `macro_rules` is a contextual keyword, it is an `IDENT` token and thus `is_path_start` already identifies it correctly. You can tell the previous check is unnecessary because the relevant tests still pass.
Use `MPlaceTy` instead of `PlaceTy` in `FnArg` and ignore (copy) locals in an
earlier step ("Locals that don't have their address taken are as protected as
they can ever be").
This seems to be crucial for tail call support (as they can't refer to caller's
locals which are killed when replacing the stack frame).
Use `ControlFlow` in visitors.
Follow up to #121256
This does have a few small behaviour changes in some diagnostic output where the visitor will now find the first match rather than the last match. The change in `find_anon_types.rs` has the only affected test. I don't see this being an issue as the last occurrence isn't any better of a choice than the first.
Refactor pre-getopts command line argument handling
Rebased version of #111658. I've also fixed the Windows CI failure (although I don't have access to Windows to test it myself).
add known-bug tests for derive failure to detect packed repr
We only taint if it was a normal item. Modules and imports are untouched. Tainting them needs to be done differently, and it's unclear if that would be useful or desirable. If we just taint them into `Res::Err`, we end up losing some duplicate name messages *in the presence of other resolution errors*.
r? `@petrochenkov`
internal: Improve readability of the parser code
The code is basically equivalent to the previous version, but it improves the readability by making it much more simpler and concise.
internal: Remove unused keyword from visibility recovery
We removed support `crate` visibility keyword, but forgot to remove it from the recovery token list.
fix: Preserve $ and \ in postfix format completions
`parse_format_exprs` doesn't escape these two as of #16781, so they have to be escaped as a separate step.
Make TAITs and ATPITs capture late-bound lifetimes in scope
This generalizes the behavior that RPITs have, where they duplicate their in-scope lifetimes so that they will always *reify* late-bound lifetimes that they capture. This allows TAITs and ATPITs to properly error when they capture in-scope late-bound lifetimes.
r? `@oli-obk` cc `@aliemjay`
Fixes#122093 and therefore https://github.com/rust-lang/rust/pull/120700#issuecomment-1981213868
Add `#[inline]` to `BTreeMap::new` constructor
This PR add the `#[inline]` attribute to `BTreeMap::new` constructor as to make it eligible for inlining.
<details>
For some context: I was profiling `rustc --check-cfg` with callgrind and due to the way we currently setup all the targets and we end-up calling `BTreeMap::new` multiple times for (nearly) all the targets. Adding the `#[inline]` attribute reduced the number of instructions needed.
</details>
Fix quadratic behavior of repeated vectored writes
Some implementations of `Write::write_vectored` in the standard library (`BufWriter`, `LineWriter`, `Stdout`, `Stderr`) check all buffers to calculate the total length. This is O(n) over the number of buffers.
It's common that only a limited number of buffers is written at a time (e.g. 1024 for `writev(2)`). `write_vectored_all` will then call `write_vectored` repeatedly, leading to a runtime of O(n²) over the number of buffers.
This fix is to only calculate as much as needed if it's needed.
Here's a test program:
```rust
#![feature(write_all_vectored)]
use std::fs::File;
use std::io::{BufWriter, IoSlice, Write};
use std::time::Instant;
fn main() {
let buf = vec![b'\0'; 100_000_000];
let mut slices: Vec<IoSlice<'_>> = buf.chunks(100).map(IoSlice::new).collect();
let mut writer = BufWriter::new(File::create("/dev/null").unwrap());
let start = Instant::now();
write_smart(&slices, &mut writer);
println!("write_smart(): {:?}", start.elapsed());
let start = Instant::now();
writer.write_all_vectored(&mut slices).unwrap();
println!("write_all_vectored(): {:?}", start.elapsed());
}
fn write_smart(mut slices: &[IoSlice<'_>], writer: &mut impl Write) {
while !slices.is_empty() {
// Only try to write as many slices as can be written
let res = writer
.write_vectored(slices.get(..1024).unwrap_or(slices))
.unwrap();
slices = &slices[(res / 100)..];
}
}
```
Before this change:
```
write_smart(): 6.666952ms
write_all_vectored(): 498.437092ms
```
After this change:
```
write_smart(): 6.377158ms
write_all_vectored(): 6.923412ms
```
`LineWriter` (and by extension `Stdout`) isn't fully repaired by this because it looks for newlines. I could open an issue for that after this is merged, I think it's fixable but not trivially.
