Clean up logic around live locals in generator analysis
Resolves#69902. Requires #71893.
I've found it difficult to make changes in the logic around live locals in `generator/transform.rs`. It uses a custom dataflow analysis, `MaybeRequiresStorage`, that AFAICT computes whether a local is either initialized or borrowed. That analysis is using `before` effects, which we should try to avoid if possible because they are harder to reason about than ones only using the unprefixed effects. @pnkfelix has suggested removing "before" effects entirely to simplify the dataflow framework, which I might pursue someday.
This PR replaces `MaybeRequiresStorage` with a combination of the existing `MaybeBorrowedLocals` and a new `MaybeInitializedLocals`. `MaybeInitializedLocals` is just `MaybeInitializedPlaces` with a coarser resolution: it works on whole locals instead of move paths. As a result, I was able to simplify the logic in `compute_storage_conflicts` and `locals_live_across_suspend_points`.
This is not exactly equivalent to the old logic; some generators are now smaller than before. I believe this was because the old logic was too conservative, but I'm not as familiar with the constraints as the original implementers were, so I could be wrong. For example, I don't see a reason the size of the `mixed_sizes` future couldn't be 5K. It went from 7K to 6K in this PR.
r? @jonas-schievink @tmandry
Improve documentation of `slice::from_raw_parts`
This is to provide a more explicit statement against a code pattern that
many people end up coming with, since the reason of it being unsound
comes from the badly known single-allocation validity rule.
Providing that very pattern as a counter-example could help mitigate that.
See also: https://internals.rust-lang.org/t/pre-rfc-add-join-seq-method-to-slices-and-strs/11936/13
r? @RalfJung
Intern predicates
Implements the first step of https://github.com/rust-lang/compiler-team/issues/285
Renames `ty::Predicate` to `ty::PredicateKind`, which is now interned.
To ease the transition, `ty::Predicate` is now a struct containing a reference
to `ty::PredicateKind`.
r? @ghost
De-abuse TyKind::Error in exhaustiveness checking
Replaces https://github.com/rust-lang/rust/pull/71074. Context: https://github.com/rust-lang/rust/issues/70866.
In order to remove the use of `TyKind::Error`, I had to make sure we skip over those fields whose inhabitedness should not be observed. This is potentially error-prone however, since we must be careful not to mix filtered and unfiltered lists of patterns. I managed to hide away most of the filtering behind a new `Fields` struct, that I used everywhere relevant. I quite like the result; I think the twin concepts of `Constructor` and `Fields` make a good mental model.
As usual, I tried to separate commits that shuffle code around from commits that require more thought to review.
cc @varkor @Centril
This is to provide a more explicit statement against a code pattern that
many people end up coming with, since the reason of it being unsound
comes from the badly known single-allocation validity rule.
Providing that very pattern as a counter-example could help mitigate that.
Co-authored-by: Ralf Jung <post@ralfj.de>
Experimentally add `ffi_const` and `ffi_pure` extern fn attributes
Add FFI function attributes corresponding to clang/gcc/... `const` and `pure`.
Rebased version of #58327 by @gnzlbg with the following changes:
- Switched back from the `c_ffi_const` and `c_ffi_pure` naming to `ffi_const` and `ffi_pure`, as I agree with https://github.com/rust-lang/rust/pull/58327#issuecomment-462718772 and this nicely aligns with `ffi_returns_twice`
- (Hopefully) took care of all of @hanna-kruppe's change requests in the original PR
r? @hanna-kruppe
Rollup of 7 pull requests
Successful merges:
- #71854 (Make `std::char` functions and constants associated to `char`.)
- #72111 (rustc-book: Document `-Z strip=val` option)
- #72272 (Fix going back in history to a search result page on firefox)
- #72296 (Suggest installing VS Build Tools in more situations)
- #72365 (Remove unused `StableHashingContext::node_to_hir_id` method)
- #72371 (FIX - Char documentation for unexperienced users)
- #72397 (llvm: Expose tiny code model to users)
Failed merges:
r? @ghost
FIX - Char documentation for unexperienced users
This is my first PR on rust and even if I've read [CONTRIBUTING.md](https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-requests) I'm ensure everything is perfect. Sorry if I didn't follow the exact procedure.
**What it does:**
- Add an example in the char documentation
**Explanation**
Unexperienced users might not know that punctuation is `Case_Ignorable` and not `Uppercase` and `Lowercase` which mean that when checking if a string is uppercase one might be tempted to write:
```rust
my_string.chars().all(char::is_uppercase)
```
However this will return false for `"HELLO WORLD"` which is not intuitive. Since the function `is_case_ignorable` doesn't exists I believe the correct way to check is:
```rust
!my_string.chars().any(char::is_lowercase)
```
The aim of this example is to prevent unexperienced users to make an error which punctuation chars.
Suggest installing VS Build Tools in more situations
When MSVC's `link.exe` wasn't found but another `link.exe` was, the error message given can be [impenetrable](https://pastebin.com/MRMCr7HM) to many users. The usual suspect is GNU's `link` tool. In this case, inform the user that they may need to install VS build tools.
This only applies when Microsoft's link tool is expected.
