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doctests
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Represent trait constness as a distinct predicate
cc `@rust-lang/project-const-traits`
r? `@ghost` for now
Also mirrored everything that is written below on this hackmd here: https://hackmd.io/`@compiler-errors/r12zoixg1l`
# Tl;dr:
* This PR removes the bulk of the old effect desugaring.
* This PR reimplements most of the effect desugaring as a new predicate and set of a couple queries. I believe it majorly simplifies the implementation and allows us to move forward more easily on its implementation.
I'm putting this up both as a request for comments and a vibe-check, but also as a legitimate implementation that I'd like to see land (though no rush of course on that last part).
## Background
### Early days
Once upon a time, we represented trait constness in the param-env and in `TraitPredicate`. This was very difficult to implement correctly; it had bugs and was also incomplete; I don't think this was anyone's fault though, it was just the limit of experimental knowledge we had at that point.
Dealing with `~const` within predicates themselves meant dealing with constness all throughout the trait solver. This was difficult to keep track of, and afaict was not handled well with all the corners of candidate assembly.
Specifically, we had to (in various places) remap constness according to the param-env constness:
https://github.com/rust-lang/rust/blob/574b64a97f52162f965bc201e47f0af8279ca65d/compiler/rustc_trait_selection/src/traits/select/mod.rs#L1498
This was annoying and manual and also error prone.
### Beginning of the effects desugaring
Later on, #113210 reimplemented a new desugaring for const traits via a `<const HOST: bool>` predicate. This essentially "reified" the const checking and separated it from any of the remapping or separate tracking in param-envs. For example, if I was in a const-if-const environment, but I wanted to call a trait that was non-const, this reification would turn the constness mismatch into a simple *type* mismatch of the effect parameter.
While this was a monumental step towards straightening out const trait checking in the trait system, it had its own issues, since that meant that the constness of a trait (or any item within it, like an associated type) was *early-bound*. This essentially meant that `<T as Trait>::Assoc` was *distinct* from `<T as ~const Trait>::Assoc`, which was bad.
### Associated-type bound based effects desugaring
After this, #120639 implemented a new effects desugaring. This used an associated type to more clearly represent the fact that the constness is not an input parameter of a trait, but a property that could be computed of a impl. The write-up linked in that PR explains it better than I could.
However, I feel like it really reached the limits of what can comfortably be expressed in terms of associated type and trait calculus. Also, `<const HOST: bool>` remains a synthetic const parameter, which is observable in nested items like RPITs and closures, and comes with tons of its own hacks in the astconv and middle layer.
For example, there are pieces of unintuitive code that are needed to represent semantics like elaboration, and eventually will be needed to make error reporting intuitive, and hopefully in the future assist us in implementing built-in traits (eventually we'll want something like `~const Fn` trait bounds!).
elaboration hack: https://github.com/rust-lang/rust/blob/8069f8d17a6c86a8fd881939fcce359a90c57ff2/compiler/rustc_type_ir/src/elaborate.rs#L133-L195
trait bound remapping hack for diagnostics: https://github.com/rust-lang/rust/blob/8069f8d17a6c86a8fd881939fcce359a90c57ff2/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs#L2370-L2413
I want to be clear that I don't think this is a issue of implementation quality or anything like that; I think it's simply a very clear sign that we're using types and traits in a way that they're not fundamentally supposed to be used, especially given that constness deserves to be represented as a first-class concept.
### What now?
This PR implements a new desugaring for const traits. Specifically, it introduces a `HostEffect` predicate to represent the obligation an impl is const, rather than using associated type bounds and the compat trait that exists for effects today.
### `HostEffect` predicate
A `HostEffect` clause has two parts -- the `TraitRef` we're trying to prove, and a `HostPolarity::{Maybe, Const}`.
`HostPolarity::Const` corresponds to `T: const Trait` bounds, which must *always* be proven as const, and which can be written in any context. These are lowered directly into the predicates of an item, since they're not "context-specific".
On the other hand, `HostPolarity::Maybe` corresponds to `T: ~const Trait` bounds which must only exist in a conditionally-const context like a method in a `#[const_trait]`, or a `const fn` free function. We do not lower these immediately into the predicates of an item; instead, we collect them into a new query called the **`const_conditions`**. These are the set of trait refs that we need to prove have const implementations for an item to be const.
Notably, they're represented as bare (poly) trait refs because they are meant to be paired back together with a `HostPolarity` when they're being registered in typeck (see next section).
For example, given:
```rust
const fn foo<T: ~const A + const B>() {}
```
`foo`'s const conditions would contain `T: A`, but not `T: B`. On the flip side, foo's predicates (`predicates_of`) query would contain `HostEffect(T: B, HostPolarity::Const)` but not `HostEffect(T: A, HostPolarity::Maybe)` since we don't need to prove that predicate in a non-const environment (and it's not even the right predicate to prove in an unconditionally const environment).
### Type checking const bodies
When type checking bodies in HIR, when we encounter a call expression, we additionally register the callee item's const conditions with the `HostPolarity` from the body we're typechecking (`Const` for unconditionally const things like `const`/`static` items, and `Maybe` for conditionally const things like const fns; and we don't register `HostPolarity` predicates for non-const bodies).
When type-checking a conditionally const body, we augment its param-env with `HostEffect(..., Maybe)` predicates.
### Checking that const impls are WF
We extend the logic in `compare_method_predicate_entailment` to also check the const-conditions of the impl method, to make sure that we error for:
```rust
#[const_trait] Bar {}
#[const_trait] trait Foo {
fn method<T: Bar>();
}
impl Foo for () {
fn method<T: ~const Bar>() {} // stronger assumption!
}
```
We also extend the WF check for impls to register the const conditions of the trait that is being implemented. This is to make sure we error for:
```rust
#[const_trait] trait Bar {}
#[const_trait] trait Foo<T> where T: ~const Bar {}
impl<T> const Foo<T> for () {}
//~^ `T: ~const Bar` is missing!
```
### Proving a `HostEffect` predicate
We have several ways of proving a `HostEffect` predicate:
1. Matching a `HostEffect` predicate from the param-env
2. From an impl - we do impl selection very similar to confirming a trait goal, except we filter for only const impls, and we additionally register the impl's const conditions (i.e. the impl's `~const` where clauses).
Later I expect that we will add more built-in implementations for things like `Fn`.
## What next?
After this PR, I'd like to split out the work more so it can proceed in parallel and probably amongst others that are not me.
* Register `HostEffect` goal for places in HIR typeck that correspond to call terminators, like autoderef.
* Make traits in libstd const again.
* Probably need to impl host effect preds in old solver.
* Implement built-in `HostEffect` rules for traits like `Fn`.
* Rip out const checking from MIR altogether.
## So what?
This ends up being super convenient basically everywhere in the compiler. Due to the design of the new trait solver, we end up having an almost parallel structure to the existing trait and projection predicates for assembling `HostEffect` predicates; adding new candidates and especially new built-in implementations is now basically trivial, and it's quite straightforward to understand the confirmation logic for these predicates.
Same with diagnostics reporting; since we have predicates which represent the obligation to prove an impl is const, we can simplify and make these diagnostics richer without having to write a ton of logic to intercept and rewrite the existing `Compat` trait errors.
Finally, it gives us a much more straightforward path for supporting the const effect on the old trait solver. I'm personally quite passionate about getting const trait support into the hands of users without having to wait until the new solver lands[^1], so I think after this PR lands we can begin to gauge how difficult it would be to implement constness in the old trait solver too. This PR will not do this yet.
[^1]: Though this is not a prerequisite or by any means the only justification for this PR.
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This allows impls such as `impl QueryData for OneOf<(T,)>`
to be displayed as variadic: `impl QueryData for OneOf<(T₁, T₂, …, Tₙ)>`.
See question on zulip:
<https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/Make.20.60.23.5Bdoc.28fake_variadic.29.5D.60.20more.20useful>
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rustdoc: adjust spacing and typography in header
Fixes #131589
Preview: https://notriddle.com/rustdoc-html-demo-12/spacing/std/index.html
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First of all, we put 4px additional margin below the search box, and 4px margin below the header to balance it out.
The bigger problem we have to solve is making the lines look logically spaced. This is troublesome, because Fira Sans (the typeface we use here) wants to look good on average, and to avoid breaking, with text that uses [ascenders and descenders](https://www.w3.org/TR/css-inline-3/images/text-edge.png). If the text we're putting in happens to not have any, things look weird (strictly speaking, there’s hand-tuning here, because the Copy Path button messes with stuff, but the overall point is that there is no true, one perfect layout).
In order to play nicely with the font, I've tweaked the text to use that space. The word "Source" for the link is now capitalized, and the Since version number now uses oldstyle nums with descenders.
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r=GuillaumeGomez
rustdoc: hash assets at rustdoc build time
Since sha256 is slow enough to show up on small benchmarks, we can save time by embedding the hash in the executable.
Addresses https://github.com/rust-lang/rust/pull/131934#issuecomment-2424213861
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rustdoc: Document `markdown` module.
Rustdoc markdown handling is currently split between:
- html::markdown, which contains all the meaty login
- markdown, which is only used for when rustdoc renders a standalone markdown file
Adds module-level doc-comment to markdown, and rename the function so it's clear that it's doing IO (instead of just rendering to a string).
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Add doc(plugins), doc(passes), etc. to INVALID_DOC_ATTRIBUTES
This fixes #82824.
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Continue to get rid of `ty::Const::{try_}eval*`
This PR mostly does:
* Removes all of the `try_eval_*` and `eval_*` helpers from `ty::Const`, and replace their usages with `try_to_*`.
* Remove `ty::Const::eval`.
* Rename `ty::Const::normalize` to `ty::Const::normalize_internal`. This function is still used in the normalization code itself.
* Fix some weirdness around the `TransmuteFrom` goal.
I'm happy to split it out further; for example, I could probably land the first part which removes the helpers, or the changes to codegen which are more obvious than the changes to tools.
r? BoxyUwU
Part of https://github.com/rust-lang/rust/issues/130704
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Remove unused `recoverable` argument in collect_intra_doc_links
r? `@notriddle`
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rustdoc: Clean up footnote handling
Best reviewed commit by commit.
Extracts footnote handling logic into it's own file (first commit) and then makes that file slightly nicer to read/understand.
No functional changes, but lays the groundwork for making more changes to footnotes (eg #131901, #131946)
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Since sha256 is slow enough to show up on small benchmarks,
we can save time by embedding the hash in the executable.
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Before this change, adding a lint was a difficult matter
because it always had some overhead involved. This was
because all lints would run, no matter their default level,
or if the user had #![allow]ed them. This PR changes that
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Rustdoc markdown handling is currently split between:
- html::markdown, which contains all the meaty login
- markdown, which is only used for when rustdoc renders a standalone
markdown file
Adds module-level doc-comment to markdown, and rename the function so
it's clear that it's doing IO (instead of just rendering to a string).
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r=aDotInTheVoid
rustdoc-JSON: Rename "object safe" to "dyn compatible"
~~Blocked: Sits atop #131594. Only the last commit is relevant.~~ (rebased)
Part of #130852.
r? aDotInTheVoid or rustdoc
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Rollup of 9 pull requests
Successful merges:
- #130989 (Don't check unsize goal in MIR validation when opaques remain)
- #131657 (Rustfmt `for<'a> async` correctly)
- #131691 (Delay ambiguous intra-doc link resolution after `Cache` has been populated)
- #131730 (Refactor some `core::fmt` macros)
- #131751 (Rename `can_coerce` to `may_coerce`, and then structurally resolve correctly in the probe)
- #131753 (Unify `secondary_span` and `swap_secondary_and_primary` args in `note_type_err`)
- #131776 (Emscripten: Xfail backtrace ui tests)
- #131777 (Fix trivially_copy_pass_by_ref in stable_mir)
- #131778 (Fix needless_lifetimes in stable_mir)
r? `@ghost`
`@rustbot` modify labels: rollup
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r=notriddle
Delay ambiguous intra-doc link resolution after `Cache` has been populated
Fixes https://github.com/rust-lang/rust/issues/130233.
I was getting nowhere with #130278. I took a wrong turn at some point and ended making way too many changes so instead I started again back from 0 and this time it worked out as expected.
r? ```@notriddle```
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rustdoc: Rename "object safe" to "dyn compatible"
Supersedes #126554:
1. In line with [T-lang's latest resolution](https://github.com/rust-lang/lang-team/issues/286#issuecomment-2338905118).
2. More comprehensive: Not only updates user-facing text but also source code.
Part of #130852.
Doesn't update rustdoc-JSON (will be filed separately).
r? `@notriddle` (rust-lang/lang-team#286) `@GuillaumeGomez` (for visibility)
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Move polarity into `PolyTraitRef` rather than storing it on the side
Arguably we could move these modifiers into `TraitRef` instead of `PolyTraitRef`, but I see `TraitRef` as simply the *path* part of the trait ref. It doesn't really matter -- refactoring this further is much easier now.
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Use environment variables instead of command line arguments for merged doctests
Fixes [#130796](https://github.com/rust-lang/rust/issues/130796).
Before merging this one, let's first ensure it has a smaller impact compared to command line arguments (results can be seen [here](https://github.com/rust-lang/rust/pull/130285)). I'll start a crater run once CI passed.
cc ``@ehuss``
r? ``@notriddle``
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r=aDotInTheVoid
rustdoc-json: change item ID's repr from a string to an int
Following [this discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/Optimizing.20the.20.60Id.60.20type.20in.20.60rustdoc-types.60), I've changed the repr of `rustdoc_json_types::Id` from a String to a u32, by adding a `clean::ItemId` interner to `JsonRenderer`
r? ``@aDotInTheVoid``
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ismailarilik:fix/rustdoc/add-space-between-struct-fields-and-their-descriptions, r=GuillaumeGomez
fix(rustdoc): add space between struct fields and their descriptions
Stolen from #128541.
Fixes #128260.
<table>
<thead>
<tr>
<th scope="col">Before</th>
<th scope="col">After</th>
</tr>
</thead>
<tbody>
<tr>
<td scope="row">
<img
src="https://github.com/user-attachments/assets/b1d3cb47-77c9-4897-a5d2-2192b11cb8a3"
/>
</td>
<td>
<img
src="https://github.com/user-attachments/assets/0b104672-d2be-49f4-ac9b-3506526fe2f1"
/>
</td>
</tr>
</tbody>
</table>
<table>
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<th scope="col">Before</th>
<th scope="col">After</th>
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<tbody>
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<td scope="row">
<img
src="https://github.com/user-attachments/assets/650c3e74-a067-492a-9ba3-557f9214f875"
/>
</td>
<td>
<img
src="https://github.com/user-attachments/assets/413ef9b0-8fca-4e16-978a-7b88d05299dc"
/>
</td>
</tr>
</tbody>
</table>
Unlike original PR, I didn't add space between field headers; I put it between headers and descriptions. So if there are only headers, the space is not changed. Otherwise, I put a space like the space between paragraphs (.75em) which makes sense for me but feel free to adjust it or ask me to do so.
r? `@GuillaumeGomez`
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Fix methods alignment on mobile
I realized that on mobile, the methods are not aligned the same depending if they have documentation or not:
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r? `@notriddle`
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Remove unneeded argument of `LinkCollector::verify_disambiguator`
Still working on https://github.com/rust-lang/rust/pull/130278. ^^'
r? `@notriddle`
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[rustdoc] Remove intra-doc links dead code
While working on https://github.com/rust-lang/rust/pull/130278, I wondered what `resolve_display_text` was doing. I removed it and ran all rustdoc tests, and nothing failed. Are some intra-doc links tests missing or is it really dead code? Couldn't figure it out.
r? `@notriddle`
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Rollup of 4 pull requests
Successful merges:
- #131331 (Revert "warn_old_master_branch" check)
- #131344 (Avoid `&Lrc<T>` in various places)
- #131346 (Restrict `ignore-mode-*` directives)
- #131353 (Add documentation for `runtest::check_rustdoc_test_option` method)
r? `@ghost`
`@rustbot` modify labels: rollup
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