docs: Correct terminology in std::cmp
This PR is the result of some discussions on URLO:
* [Traits in `std::cmp` and mathematical terminology](https://users.rust-lang.org/t/traits-in-std-cmp-and-mathematical-terminology/69887)
* [Are poker hands `Ord` or `PartialOrd`?](https://users.rust-lang.org/t/are-poker-hands-ord-or-partialord/82644)
Arguably, the documentation currently isn't very precise regarding mathematical terminology. This can lead to misunderstandings of what `PartialEq`, `Eq`, `PartialOrd`, and `Ord` actually do.
While I believe this PR doesn't give any new API guarantees, it expliclitly mentions that `PartialEq::eq(a, b)` may return `true` for two distinct values `a` and `b` (i.e. where `a` and `b` are not equal in the mathematical sense). This leads to the consequence that `Ord` may describe a weak ordering instead of a total ordering.
In either case, I believe this PR should be thoroughly reviewed, ideally by someone with mathematical background to make sure the terminology is correct now, and also to ensure that no unwanted new API guarantees are made.
In particular, the following problems are addressed:
* Some clarifications regarding used (mathematical) terminology:
* Avoid using the terms "total equality" and "partial equality" in favor of "equivalence relation" and "partial equivalence relation", which are well-defined and unambiguous.
* Clarify that `Ordering` is an ordering between two values (and not an order in the mathematical sense).
* Avoid saying that `PartialEq` and `Eq` are "equality comparisons" because the terminology "equality comparison" could be misleading: it's possible to implement `PartialEq` and `Eq` for other (partial) equivalence relations, in particular for relations where `a == b` for some `a` and `b` even when `a` and `b` are not the same value.
* Added a section "Strict and non-strict partial orders" to document that the `<=` and `>=` operators do not correspond to non-strict partial orders.
* Corrected section "Corollaries" in documenation of `Ord` in regard to `<` only describing a strict total order in cases where `==` conforms to mathematical equality.
* ~~Added a section "Weak orders" to explain that `Ord` may also describe a weak order or total preorder, depending on how `PartialEq::eq` has been implemented.~~ (Removed, see [comment](https://github.com/rust-lang/rust/pull/103046#issuecomment-1279929676))
* Made documentation easier to understand:
* Explicitly state at the beginning of `PartialEq`'s documentation comment that implementing the trait will provide the `==` and `!=` operators.
* Added an easier to understand rule when to implement `Eq` in addition to `PartialEq`: "if it’s guaranteed that `PartialEq::eq(a, a)` always returns `true`."
* Explicitly mention in documentation of `Eq` that the properties "symmetric" and "transitive" are already required by `PartialEq`.
core library: Disable fpmath tests for i586 ...
This patch disables the floating-point epsilon test for i586 since x87 registers are too imprecise and can't produce the expected results.
Some clarifications regarding used (mathematical) terminology:
* Avoid using the terms "total equality" and "partial equality" in favor
of "equivalence relation" and "partial equivalence relation", which
are well-defined and unambiguous.
* Clarify that `Ordering` is an ordering between two values (and not an
order in the mathematical sense).
* Avoid saying that `PartialEq` and `Eq` are "equality comparisons"
because the terminology "equality comparison" could be misleading:
it's possible to implement `PartialEq` and `Eq` for other (partial)
equivalence relations, in particular for relations where `a == b` for
some `a` and `b` even when `a` and `b` are not the same value.
* Added a section "Strict and non-strict partial orders" to document
that the `<=` and `>=` operators do not correspond to non-strict
partial orders.
* Corrected section "Corollaries" in documenation of Ord in regard to
`<` only describing a strict total order in cases where `==` conforms
to mathematical equality.
Made documentation easier to understand:
* Explicitly state at the beginning of `PartialEq`'s documentation
comment that implementing the trait will provide the `==` and `!=`
operators.
* Added an easier to understand rule when to implement `Eq` in addition
to `PartialEq`: "if it’s guaranteed that `PartialEq::eq(a, a)` always
returns `true`."
* Explicitly mention in documentation of `Eq` that the properties
"symmetric" and "transitive" are already required by `PartialEq`.
Rollup of 5 pull requests
Successful merges:
- #116223 (Fix misuses of a vs an)
- #116296 (More accurately point to where default return type should go)
- #116429 (Diagnostics: Be more careful when suggesting struct fields)
- #116431 (Tweak wording of E0562)
- #116432 (rustdoc: rename `issue-\d+.rs` tests to have meaningful names (part 2))
r? `@ghost`
`@rustbot` modify labels: rollup
Diagnostics: Be more careful when suggesting struct fields
Consolidate the various places which filter out struct fields that shouldn't be suggested into a single function.
Previously, each of those code paths had slightly different and incomplete metrics for no good reason. Now, there's only a single 'complete' metric (namely `is_field_suggestable`) which also filters out hygienic fields that come from different syntax contexts.
Fixes#116334.
More accurately point to where default return type should go
When getting the "default return type" span, instead of pointing to the low span of the next token, point to the high span of the previous token. This:
1. Makes forming return type suggestions more uniform, since we expect them all in the same place.
2. Arguably makes labels easier to understand, since we're pointing to where the implicit `-> ()` would've gone, rather than the starting brace or the semicolon.
r? ```@estebank```
Currently `rust_20XX_preview` features aren't recorded as declared even
when they are explicit declared. Similarly, redundant edition-dependent
features (e.g. `test_2018_feature`) aren't recorded as declared.
This commit marks them as recorded. There is no detectable functional
change, but it makes things more consistent.
The word "active" is currently used in two different and confusing ways:
- `ACTIVE_FEATURES` actually means "available unstable features"
- `Features::active_features` actually means "features declared in the
crate's code", which can include feature within `ACTIVE_FEATURES` but
also others.
(This is also distinct from "enabled" features which includes declared
features but also some edition-specific features automatically enabled
depending on the edition in use.)
This commit changes the `Features::active_features` to
`Features::declared_features` which actually matches its meaning.
Likewise, `Features::active` becomes `Features::declared`.
The new way of doing things:
- Avoids some code duplication.
- Distinguishes the `crate_edition` (which comes from `--edition`) and
the `features_edition` (which combines `--edition` along with any
`rustc_20XX_preview` features), which is useful.
- Has a simpler initial loop, one that just looks for
`rustc_20XX_preview` features in order to compute `features_edition`.
- Creates a fallible alternative to `Features::enabled`, which is
useful.
It's not easy to see how exactly the old and new code are equivalent,
but it's reassuring to know that the test coverage is quite good for
this stuff.
There is a single features (`no_stack_check`) in
`STABLE_REMOVED_FEATURES`. But the treatment of
`STABLE_REMOVED_FEATURES` and `REMOVED_FEATURES` is actually identical.
So this commit just merges them, and uses a comment to record
`no_stack_check`'s unique "stable removed" status.
This also lets `State::Stabilized` (which was a terrible name) be
removed.
It currently processes `ACTIVE_FEATURES` separately from
`ACCEPTED_FEATURES`, `REMOVED_FEATURES`, and `STABLE_REMOVED_FEATURES`,
for no good reason. This commit treats them uniformly.
It's a macro with four clauses, three of which are doing one thing, and
the fourth is doing something completely different. This commit splits
it into two macros, which is more sensible.
Remove the `TypedArena::alloc_from_iter` specialization.
It was added in #78569. It's complicated and doesn't actually help
performance.
r? `@cjgillot`
Matthias Krüger