Add some performance guidance to std::fs and std::io docs
Adds more documentation about performance to various "read" functions in `fs` and `io`, and to `BufReader`/`BufWriter`, with the goal of helping developers choose the best option for a given task.
Re-write the documentation index
The docs team has decided that we're framing resources in three ways:
"learning Rust," "using Rust," "mastering Rust." This is a more useful
split than "beginner/intermediate/advanced." As we add more resources
in the future, we expect "using Rust" to grow. "the bookshelf" as a
concept is great, but isn't really organized along these lines. As such,
this reorganizes the docs along these lines.
avoid IdxSets containing garbage above the universe length
This makes sure that all bits in each IdxSet between the universe length
and the end of the word are all zero instead of being in an indeterminate state.
This fixes a crash with RUST_LOG=rustc_mir, and is probably a good idea
anyway.
r? @nikomatsakis - I think you are responsible for this code area now?
Introduce Vec::resize_with method (see #41758)
In #41758, the libs team decided they preferred `Vec::resize_with` over `Vec::resize_default()`. Here is an implementation to get this moving forward.
I don't know what the removal process for `Vec::resize_default()` should be, so I've left it in place for now. Would be happy to follow up with its removal.
Add #[must_use] to a few standard library methods
Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.
Discuss :)
```rust
warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
--> $DIR/fn_must_use_stdlib.rs:19:5
|
LL | "1 2 3".split_whitespace().collect::<Vec<_>>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
--> $DIR/fn_must_use_stdlib.rs:21:5
|
LL | "hello".to_owned();
| ^^^^^^^^^^^^^^^^^^^
warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
--> $DIR/fn_must_use_stdlib.rs:23:5
|
LL | String::from("world").clone();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
cc https://github.com/rust-lang/rust/issues/48926
rustc_driver: get rid of the extra thread
**Do not rollup**
We can alter the stack size afterwards on Unix.
Having a separate thread causes poor debugging experience when interrupting with signals. I have to get the backtrace of the all thread, as the main thread is waiting to join doing nothing else. This patch allows me to just run `bt` to get the desired backtrace.
Reject huge alignments on macos with system allocator only
ef8804ba27 addressed #30170 by rejecting
huge alignments at the allocator API level, transforming a specific
platform bug/limitation into an enforced API limitation on all
platforms.
This change essentially reverts that commit, and instead makes alloc()
itself return AllocErr::Unsupported when receiving huge alignments.
This was discussed in https://github.com/rust-lang/rust/issues/32838#issuecomment-368348408
and following.
Update sccache to its master branch
Ideally I'd like to soon enable sccache for rustbuild itself and some of the
stage0 tools, but for that to work we'll need some better Rust support than the
pretty old version we were previously using!
The docs team has decided that we're framing resources in three ways:
"learning Rust," "using Rust," "mastering Rust." This is a more useful
split than "beginner/intermediate/advanced." As we add more resources
in the future, we expect "using Rust" to grow. "the bookshelf" as a
concept is great, but isn't really organized along these lines. As such,
this reorganizes the docs along these lines.
Remove adjacent all-const match arm hack.
An old fix for moves-in-guards had a hack for adjacent all-const match arms.
The hack was explained in a comment, which you can see here:
https://github.com/rust-lang/rust/pull/22580/files#diff-402a0fa4b3c6755c5650027c6d4cf1efR497
But hack was incomplete (and thus unsound), as pointed out here:
https://github.com/rust-lang/rust/issues/47295#issuecomment-357108458
Plus, it is likely to be at least tricky to reimplement this hack in
the new NLL borrowck.
So rather than try to preserve the hack, we want to try to just remove
it outright. (At least to see the results of a crater run.)
[breaking-change]
This is a breaking-change, but our hope is that no one is actually
relying on such an extreme special case. (We hypothesize the hack was
originally added to accommodate a file in our own test suite, not code
in the wild.)
Extend two-phase borrows to apply to method receiver autorefs
Fixes#48598 by permitting two-phase borrows on the autorefs created when functions and methods.
Add Iterator::find_map
I'd like to propose to add `find_map` method to the `Iterator`: an occasionally useful utility, which relates to `filter_map` in the same way that `find` relates to `filter`.
`find_map` takes an `Option`-returning function, applies it to the elements of the iterator, and returns the first non-`None` result. In other words, `find_map(f) == filter_map(f).next()`.
Why do we want to add a function to the `Iterator`, which can be trivially expressed as a combination of existing ones? Observe that `find(f) == filter(f).next()`, so, by the same logic, `find` itself is unnecessary!
The more positive argument is that desugaring of `find[_map]` in terms of `filter[_map]().next()` is not super obvious, because the `filter` operation reads as if it is applies to the whole collection, although in reality we are interested only in the first element. That is, the jump from "I need a **single** result" to "let's use a function which maps **many** values to **many** values" is a non-trivial speed-bump, and causes friction when reading and writing code.
Does the need for `find_map` arise in practice? Yes!
* Anecdotally, I've more than once searched the docs for the function with `[T] -> (T -> Option<U>) -> Option<U>` signature.
* The direct cause for this PR was [this](1291c50e86 (r174934173)) discussion in Cargo, which boils down to "there's some pattern that we try to express here, but current approaches looks non-pretty" (and the pattern is `filter_map`
* There are several `filter_map().next` combos in Cargo: [[1]](545a4a2c93/src/cargo/ops/cargo_new.rs (L585)), [[2]](545a4a2c93/src/cargo/core/resolver/mod.rs (L1130)), [[3]](545a4a2c93/src/cargo/ops/cargo_rustc/mod.rs (L1086)).
* I've also needed similar functionality in `Kotlin` several times. There, it is expressed as `mapNotNull {}.firstOrNull`, as can be seen [here](ee8bdb4e07/src/main/kotlin/org/rust/cargo/project/model/impl/CargoProjectImpl.kt (L154)), [here](ee8bdb4e07/src/main/kotlin/org/rust/lang/core/resolve/ImplLookup.kt (L444)) [here](ee8bdb4e07/src/main/kotlin/org/rust/ide/inspections/RsLint.kt (L38)) and [here](ee8bdb4e07/src/main/kotlin/org/rust/cargo/toolchain/RustToolchain.kt (L74)) (and maybe in some other cases as well)
Note that it is definitely not among the most popular functions (it definitely is less popular than `find`), but, for example it (in case of Cargo) seems to be more popular than `rposition` (1 occurrence), `step_by` (zero occurrences) and `nth` (three occurrences as `nth(0)` which probably should be replaced with `next`).
Do we necessary need this function in `std`? Could we move it to itertools? That is possible, but observe that `filter`, `filter_map`, `find` and `find_map` together really form a complete table:
|||
|-------|---------|
| filter| find|
|filter_map|find_map|
It would be somewhat unsatisfying to have one quarter of this table live elsewhere :) Also, if `Itertools` adds an `find_map` method, it would be more difficult to move it to std due to name collision.
Hm, at this point I've searched for `filter_map` the umpteenth time, and, strangely, this time I do find this RFC: https://github.com/rust-lang/rfcs/issues/1801. I guess this could be an implementation though? :)
To sum up:
Pro:
- complete the symmetry with existing method
- codify a somewhat common non-obvious pattern
Contra:
- niche use case
- we can, and do, live without it
