Trait documentation clarifications
Hi! I've felt a bit of friction lately in figuring out how to write custom implementations of the `derive`able traits, so I decided to add to the docs :)
The docs for `Copy` are already excellent-- clear, useful sections that I only reordered a bit-- they're now:
* General explanation
* When can my type be `Copy`?
* When can my type _not_ be `Copy`?
* When should my type be `Copy`?
* Derivable
* How can I implement `Copy`?
I didn't add all these sections for all the traits, but I did make sure all the derivable traits had a consistent "Derivable" section that explained what the derived implementation does and a "How can I implement" section that has an example.
Please check me for correctness-- I tried to do research to make sure I was saying accurate things but I'm still learning! ❤️ I'd also love suggestions on information to add that is still missing-- I think these traits are important and deserve to have awesome docs!
Fixes to mir dataflow
Fixes to mir dataflow
This collects a bunch of changes to `rustc_borrowck::borrowck::dataflow` (which others have pointed out should probably migrate to some crate that isn't tied to the borrow-checker -- but I have not attempted that here, especially since there are competing approaches to dataflow that we should also evaluate).
These changes:
1. Provide a family of related analyses: MovingOutStatements (which is what the old AST-based dataflo computed), as well as MaybeInitialized, MaybeUninitalized, and DefinitelyInitialized.
* (The last two are actually inverses of each other; we should pick one and drop the other.)
2. Fix bugs in the pre-existing analysis implementation, which was untested and thus some obvious bugs went unnoticed, which brings us to the third point:
3. Add a unit test infrastructure for the MIR dataflow analysis.
* The tests work by adding a new intrinsic that is able to query the analysis state for a particular expression (technically, a particular L-value).
* See the examples in compile-fail/mir-dataflow/inits-1.rs and compile-fail/mir-dataflow/uninits-1.rs
* These tests are only checking the results for MaybeInitialized, MaybeUninitalized, and DefinitelyInitialized; I am not sure if it will be feasible to generalize this testing strategy to the MovingOutStatements dataflow operator.
Add explicit "Derivable" and "How can I implement `Default`" sections.
Copied relevant sections from the module-level documentation, but also
linked to there-- it has a more comprehensive narrative with examples
that show implementation AND use. Decided to just put implementation
example in the trait documentation.
The new order puts all the "when" questions together and puts the "how"
question with the "derivable" section. So you have to scroll past (and
hopefully read) the can/cannot/should caveats and guidelines to get to
the information about how to actually go about doing it once you've
determined that you can and should, with derivable information first so
that you can just use the derived implementation if that applies.
Previous order:
* General explanation
* When can my type be `Copy`?
* How can I implement `Copy`?
* When can my type _not_ be `Copy`?
* When should my type be `Copy`?
* Derivable
New order:
* General explanation
* When can my type be `Copy`?
* When can my type _not_ be `Copy`?
* When should my type be `Copy`?
* Derivable
* How can I implement `Copy`?
I think these just got out of sync, but both use a lexicographic
ordering.
Relevant commits in the history of these explanations:
* 8b81f76 on 2015-06-30
* e22770b on 2016-02-09
Implement `last` for `EscapeUnicode`
The implementation is quite trivial as the last character is always `'{'`.
As a side-effect it also improves the implementation of `last` for `EscapeUnicode`.
Part of #24214, split from #31049.
Maybe this (and the other changes that I will split from #31049) should wait for a test like `ed_iterator_specializations` to be added. Would it be sufficient to do the same for each possible escape length?
Fix fast path of float parsing on x87
The fast path of the float parser relies on the rounding to happen
exactly and directly to the correct number of bits. On x87, instead,
double rounding would occour as the FPU stack defaults to 80 bits of
precision.
This can be fixed by setting the precision of the FPU stack before
performing the int to float conversion. This can be achieved by
changing the value of the x87 control word. This is a somewhat common
operation that is in fact performed whenever a float needs to be
truncated to an integer, but it is undesirable to add its overhead for
code that does not rely on x87 for computations (i.e. on non-x86
architectures, or x86 architectures which perform FPU computations on
using SSE).
Fixes `num::dec2flt::fast_path_correct` (on x87).
Remove irrelevant information (and instead provide pointer to
reference documentation), replace ASCII-art table with the
corresponding MarkDown one, and minor fixes.
Make AtomicBool the same size as bool
Reopening #32365
This allows `AtomicBool` to be transmuted to a `bool`, which makes it more consistent with the other atomic types. Note that this now guarantees that the atomic type will always contain a valid `bool` value, which wasn't the case before (due to `fetch_nand`).
r? @alexcrichton
Explain the meaning of the fields of the control word and provide more
details about how the relevant one (Precision Control) is updated in
the fast path.
The fast path of the float parser relies on the rounding to happen
exactly and directly to the correct number of bits. On x87, instead,
double rounding would occour as the FPU stack defaults to 80 bits of
precision.
This can be fixed by setting the precision of the FPU stack before
performing the int to float conversion. This can be achieved by
changing the value of the x87 control word. This is a somewhat common
operation that is in fact performed whenever a float needs to be
truncated to an integer, but it is undesirable to add its overhead for
code that does not rely on x87 for computations (i.e. on non-x86
architectures, or x86 architectures which perform FPU computations on
using SSE).
Fixes `num::dec2flt::fast_path_correct` (on x87).
rustbuild: Add support for crate tests + doctests
This commit adds support to rustbuild to run crate unit tests (those defined by
`#[test]`) as well as documentation tests. All tests are powered by `cargo test`
under the hood.
Each step requires the `libtest` library is built for that corresponding stage.
Ideally the `test` crate would be a dev-dependency, but for now it's just easier
to ensure that we sequence everything in the right order.
Currently no filtering is implemented, so there's not actually a method of
testing *only* libstd or *only* libcore, but rather entire swaths of crates are
tested all at once.
A few points of note here are:
* The `coretest` and `collectionstest` crates are just listed as `[[test]]`
entires for `cargo test` to naturally pick up. This mean that `cargo test -p
core` actually runs all the tests for libcore.
* Libraries that aren't tested all mention `test = false` in their `Cargo.toml`
* Crates aren't currently allowed to have dev-dependencies due to
rust-lang/cargo#860, but we can likely alleviate this restriction once
workspaces are implemented.
cc #31590
This commit adds support to rustbuild to run crate unit tests (those defined by
`#[test]`) as well as documentation tests. All tests are powered by `cargo test`
under the hood.
Each step requires the `libtest` library is built for that corresponding stage.
Ideally the `test` crate would be a dev-dependency, but for now it's just easier
to ensure that we sequence everything in the right order.
Currently no filtering is implemented, so there's not actually a method of
testing *only* libstd or *only* libcore, but rather entire swaths of crates are
tested all at once.
A few points of note here are:
* The `coretest` and `collectionstest` crates are just listed as `[[test]]`
entires for `cargo test` to naturally pick up. This mean that `cargo test -p
core` actually runs all the tests for libcore.
* Libraries that aren't tested all mention `test = false` in their `Cargo.toml`
* Crates aren't currently allowed to have dev-dependencies due to
rust-lang/cargo#860, but we can likely alleviate this restriction once
workspaces are implemented.
cc #31590
Add rustc_on_unimplemented for Index implementation on slice
Reopening of #31071.
It also extends the possibility of `#[rustc_on_unimplemented]` by providing a small type filter in order to find the ones which corresponds the most.
r? @pnkfelix
