Rollup of 9 pull requests
Successful merges:
- #69860 (Use associated numeric consts in documentation)
- #70576 (Update the description of the ticket to point at RFC 1721)
- #70597 (Fix double-free and undefined behaviour in libstd::syn::unix::Thread::new)
- #70640 (Hide `task_context` when lowering body)
- #70641 (Remove duplicated code in trait selection)
- #70707 (Remove unused graphviz emitter)
- #70720 (Place TLS initializers with relocations in .tdata)
- #70735 (Clean up E0502 explanation)
- #70741 (Add test for #59023)
Failed merges:
r? @ghost
Place TLS initializers with relocations in .tdata
Should fix#70673, although I'm not sure how to test this. Perhaps @joshlf could find a MCVE?
Also adds more context to the FIXME.
r? @oli-obk
Fix double-free and undefined behaviour in libstd::syn::unix::Thread::new
While working on concurrency support for Miri, I found that the `libstd::syn::unix::Thread::new` method has two potential problems: double-free and undefined behaviour.
**Double-free** could occur if the following events happened (credit for pointing this out goes to @RalfJung):
1. The call to `pthread_create` successfully launched a new thread that executed to completion and deallocated `p`.
2. The call to `pthread_attr_destroy` returned a non-zero value causing the `assert_eq!` to panic.
3. Since `mem::forget(p)` was not yet executed, the destructor of `p` would be executed and cause a double-free.
As far as I understand, this code also violates the stacked-borrows aliasing rules and thus would result in **undefined behaviour** if these rules were adopted. The problem is that the ownership of `p` is passed to the newly created thread before the call to `mem::forget`. Since the call to `mem::forget` is still a call, it counts as a use of `p` and triggers UB.
This pull request changes the code to use `mem::ManuallyDrop` instead of `mem::forget`. As a consequence, in case of a panic, `p` would be potentially leaked, which while undesirable is probably better than double-free or undefined behaviour.
Use associated numeric consts in documentation
Now when the associated constants on int/float types are stabilized and the recommended way of accessing said constants (#68952). We can start using it in this repository, and recommend it via documentation example code.
This PR is the reincarnation of #67913 minus the actual adding + stabilization of said constants. (EDIT: Now it's only changing the documentation. So users will see the new consts, but we don't yet update the internal code)
Because of how fast bit rot happens to PRs that touch this many files, it does not try to replace 100% of the old usage of the constants in the entire repo, but a good chunk of them.
