Dont collect assoc ty item bounds from trait where clause for host effect predicates
For background, we uplift `where Self::Assoc: Trait` bounds in a trait's where clauses into *item bounds* on `type Assoc;`. This is because before we *had* syntactical item bounds, users would express their item bounds like so.
Let's opt out of doing this same behavior for `HostEffect` predicates like `where Self::Assoc: [const] Trait`. I left a comment in the code:
```rust
// FIXME(const_trait_impl): We *could* uplift the
// `where Self::Assoc: [const] Trait` bounds from the parent trait
// here too, but we'd need to split `const_conditions` into two
// queries (like we do for `trait_explicit_predicates_and_bounds`)
// since we need to also filter the predicates *out* of the const
// conditions or they lead to cycles in the trait solver when
// utilizing these bounds. For now, let's do nothing.
```
As an aside, this was an ICE that was only triggerable when building libraries and not binaries because we never were calling `tcx.ensure_ok().explicit_implied_const_bounds(def_id);` on associated types like we should have been. I adjusted the calls to `ensure_ok` to make sure this happens, so we catch bugs like this in the future more easily.
As another aside, I fixed the bound uplifting logic for *always const* predicates, since those act like normal clauses and have no notion of conditional constness.
r? ```@oli-obk``` ```@fee1-dead``` or anyone really
Fixesrust-lang/rust#133275
Implement unstable trait impl
This PR allows marking impls of stable trait with stable type as unstable.
## Approach
In std/core, an impl can be marked as unstable by annotating it with ``#[unstable_feature_bound(feat_name)]``. This will add a ``ClauseKind::Unstable_Feature(feat_name)`` to the list of predicates in ``predicates_of`` .
When an unstable impl's function is called, we will first iterate through all the goals in ``param_env`` to check if there is any ``ClauseKind::UnstableFeature(feat_name)`` in ``param_env``.
The existence of ``ClauseKind::Unstable_Feature(feat_name)`` in ``param_env`` means an``#[unstable_feature_bound(feat_name)]`` is present at the call site of the function, so we allow the check to succeed in this case.
If ``ClauseKind::UnstableFeature(feat_name)`` does not exist in ``param_env``, we will still allow the check to succeed for either of the cases below:
1. The feature is enabled through ``#[feature(feat_name)]`` outside of std / core.
2. We are in codegen because we may be monomorphizing a body from an upstream crate which had an unstable feature enabled that the downstream crate do not.
For the rest of the case, it will fail with ambiguity.
## Limitation
In this PR, we do not support:
1. using items that need ``#[unstable_feature_bound]`` within stable APIs
2. annotate main function with ``#[unstable_feature_bound]``
3. annotate ``#[unstable_feature_bound]`` on items other than free function and impl
## Acknowledgement
The design and mentoring are done by `@BoxyUwU`
de-duplicate condition scoping logic between AST→HIR lowering and `ScopeTree` construction
There was some overlap between `rustc_ast_lowering::LoweringContext::lower_cond` and `rustc_hir_analysis::check::region::resolve_expr`, so I've removed the former and migrated its logic to the latter, with some simplifications.
Consequences:
- For `while` and `if` expressions' `let`-chains, this changes the `HirId`s for the `&&`s to properly correspond to their AST nodes. This is how guards were handled already.
- This makes match guards share previously-duplicated logic with `if`/`while` expressions. This will also be used by guard pattern[^1] guards.
- Aside from legacy syntax extensions (e.g. some builtin macros) that directly feed AST to the compiler, it's currently impossible to put attributes directly on `&&` operators in `let` chains[^2]. Nonetheless, attributes on `&&` operators in `let` chains in `if`/`while` expression conditions are no longer silently ignored and will be lowered.
- This no longer wraps conditions in `DropTemps`, so the HIR and THIR will be slightly smaller.
- `DesugaringKind::CondTemporary` is now gone. It's no longer applied to any spans, and all uses of it were dead since they were made to account for `if` and `while` being desugared to `match` on a boolean scrutinee.
- Should be a marginal perf improvement beyond that due to leveraging [`ScopeTree` construction](5e749eb66f/compiler/rustc_hir_analysis/src/check/region.rs (L312-L355))'s clever handling of `&&` and `||`:
- This removes some unnecessary terminating scopes that were placed around top-level `&&` and `||` operators in conditions. When lowered to MIR, logical operator chains don't create intermediate boolean temporaries, so there's no temporary to drop. The linked snippet handles wrapping the operands in terminating scopes as necessary, in case they create temporaries.
- The linked snippet takes care of letting `let` temporaries live and terminating other operands, so we don't need separate traversals of `&&` chains for that.
[^1]: rust-lang/rust#129967
[^2]: Case-by-case, here's my justification: `#[attr] e1 && e2` applies the attribute to `e1`. In `#[attr] (e1 && e2)` , the attribute is on the parentheses in the AST, plus it'd fail to parse if `e1` or `e2` contains a `let`. In `#[attr] expands_to_let_chain!()`, the attribute would already be ignored (rust-lang/rust#63221) and it'd fail to parse anyway; even if the expansion site is a condition, the expansion wouldn't be parsed with `Restrictions::ALLOW_LET`. If it *was* allowed, the notion of a "reparse context" from https://github.com/rust-lang/rust/issues/61733#issuecomment-509626449 would be necessary in order to make `let`-chains left-associative; multiple places in the compiler assume they are.
Port several trait/coherence-related attributes the new attribute system
Part of rust-lang/rust#131229
This ports:
- `#[const_trait]`
- `#[rustc_deny_explicit_impl]`
- `#[rustc_do_not_implement_via_object]`
- `#[rustc_coinductive]`
- `#[type_const]`
- `#[rustc_specialization_trait]`
- `#[rustc_unsafe_specialization_marker]`
- `#[marker]`
- `#[fundamental]`
- `#[rustc_paren_sugar]`
- `#[rustc_allow_incoherent_impl]`
- `#[rustc_coherence_is_core]`
This also changes `#[marker]` to error on duplicates instead of warning.
cc rust-lang/rust#142838, but I don't think it matters too much, since it's unstable.
r? ``@oli-obk``
compiler: rename BareFn to FnPtr
At some point "BareFn" was the chosen name for a "bare" function, without the niceties of `~fn`, `&fn`, or a few other ways of writing a function type. However, at some point the syntax for a "bare function" and any other function diverged even more. We started calling them what they are: function pointers, denoted by their own syntax.
However, we never changed the *internal* name for these, as this divergence was very gradual. Personally, I have repeatedly searched for "FnPtr" and gotten confused until I find the name is BareFn, only to forget this until the next time, since I don't routinely interact with the higher-level AST and HIR. But even tools that interact with these internal types only touch on them in a few places, making a migration easy enough. Let's use a more intuitive and obvious name, as this 12+ year old name has little to do with current Rust.
Fix some comments and related types and locals where it is obvious, e.g.
- bare_fn -> fn_ptr
- LifetimeBinderKind::BareFnType -> LifetimeBinderKind::FnPtrType
Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>
Remove `Symbol` from `Named` variant of `BoundRegionKind`/`LateParamRegionKind`
The `Symbol` is redundant, since we already store a `DefId` in the region variant. Instead, load the name via `item_name` when needed (which is almost always on the diagnostic path).
This introduces a `BoundRegionKind::NamedAnon` which is used for giving anonymous bound regions names, but which should only be used during pretty printing and error reporting.
compiler: Document and reduce `fn provide`s in hir crates
I found it hard to follow all these tiny micro-indirections. Much like you shouldn't pass around `&u32` if you can help it, you probably shouldn't use an indirection if the indirection overhead itself is literally bigger than the amount of data you are organizing. Generally a new `fn provide` amounts to around 3 LOC:
- the signature with opening brace
- the `rustc_middle::query::Providers` import
- an end brace
I am not even counting the cost in time and thought to go find the other `provide`, read it, understand, "Ah, yes, these functions", and then go to those. Thus I say we should collapse indirections of `provide` for modules that only export 1~2 queries. For higher-count indirections, I left them as-is, as I don't understand the crate well enough to judge their worth.
Then I dropped a pointer to the actual module of interest for all these instances of the same function. I think documenting them is important because the comment that it relates to the query system makes it obvious that they have **nothing** to do with the rest of the module's logic and I can carry on ignoring them. Actively doing so is another cognitive cost, but much more minimal.
There is also a small correctness issue in that all of these functions are technically mutating state. It's not a huge deal, but it's still easier to check all these mutations do not overlap if we have less instances of `fn provide` to check.
Many small indirections with 1-2 items actively hinders understanding.
Inlines various tiny submodule provides into
- hir_analysis::provide
- hir_analysis::check::provide
- hir_typeck::provide
