Index 0 must be a valid char boundary (invariant of str that it contains
valid UTF-8 data).
If we check explicitly for index == 0, that removes the need to read the
byte at index 0, so it avoids a trip to the string's memory, and it
optimizes out the slicing index' bounds check whenever it is zero.
With this change, the following examples all change from having a read of
the byte at 0 and a branch to possibly panicing, to having the bounds
checking optimized away.
```rust
pub fn split(s: &str) -> (&str, &str) {
s.split_at(0)
}
pub fn both(s: &str) -> &str {
&s[0..s.len()]
}
pub fn first(s: &str) -> &str {
&s[..0]
}
pub fn last(s: &str) -> &str {
&s[0..]
}
```
It's nice to be able to index with a scope-id,
but coherence rules prevent us from implementing
`Index<ScopeId>` for `Vec<ScopeAuxiliary>`, and I'd
prefer that `ScopeAuxiliary` remain in librustc_mir,
just for compilation time reasons.
This was triggered by me wanting to address a use of DUMMY_SP, but
actually I'm not sure what would be a better span -- I guess the span
for the function as a whole.
Docs: Change "statements" to "expressions" on `match`
I apt to use `expressions` over `statements`, because `match` is a expression in essence, though it can become a statement when followed a semicolon.
Annotate run-pass/backtrace with #[rustc_no_mir] on MSVC.
Fixes#32384 by not using MIR on MSVC for the functions in the path of the backtrace.
This is the known blocker for the MSVC MIR builder, hopefully the only one overall.
r? @alexcrichton Confirmed to work on a nightly, by @retep998.
rustdoc: Consider `doc(no_inline)` in crate-local inlining
Imports with `doc(no_inline)` will not be inlined, even when `doc(inline)` is present.
fixes#32343
r? @alexcrichton
Simplifying some of the phrasing explaining lifetime elision
Just simplifying some of the language expressing what kind of inference Rust can and can't do on function signatures.
Fix const trans
Fix#30615.
The idea was that when there are N autoderefs, first do N-1 derefs and check for autoref. If there is autoref, done, if not, do one more deref. But when N is zero, doing one more deref is wrong.
std: Store flowinfo/scope_id in host byte order
Apparently these aren't supposed to be stored in network byte order, so doing so
ends up causing failures when it would otherwise succeed when stored in the host
byte order.
Closes#32424
convert 99.9% of `try!`s to `?`s
The first commit is an automated conversion using the [untry] tool and the following command:
```
$ find -name '*.rs' -type f | xargs untry
```
at the root of the Rust repo.
[untry]: https://github.com/japaric/untry
cc @rust-lang/lang @alexcrichton @brson
Introduce 'cargotest' and the check-cargotest buildstep
This is a new suite of tests that verifies that the compiler builds specific revisions of select crates from crates.io.
It does not run by default. It is intended that bors runs these tests against all PRs, and gates on them. In this way we will make it harder still to break important swaths of the ecosystem, even on nightly.
This is a very basic implementation intended for feedback. The biggest thing it probably should do but doesn't is use a lockfile for every project it builds.
r? @alexcrichton cc @rust-lang/lang @rust-lang/libs
They were probably meant as a shorthand for omitted code.
Part of #32446 but there should be a separate fix for the issue.
Signed-off-by: NODA, Kai <nodakai@gmail.com>
