rustc_codegen_llvm: replace the first argument early in FnType::new_vtable.
Fixes#51907 by removing the vtable pointer before the `ArgType` is even created.
This allows any ABI to support trait object method calls, regardless of how it passes `*dyn Trait`.
r? @nikomatsakis
Rollup of 14 pull requests
Successful merges:
- #51614 (Correct suggestion for println)
- #51952 ( hygiene: Decouple transparencies from expansion IDs)
- #52193 (step_by: leave time of item skip unspecified)
- #52207 (improve error message shown for unsafe operations)
- #52223 (Deny bare trait objects in in src/liballoc)
- #52224 (Deny bare trait objects in in src/libsyntax)
- #52239 (Remove sync::Once::call_once 'static bound)
- #52247 (Deny bare trait objects in in src/librustc)
- #52248 (Deny bare trait objects in in src/librustc_allocator)
- #52252 (Deny bare trait objects in in src/librustc_codegen_llvm)
- #52253 (Deny bare trait objects in in src/librustc_data_structures)
- #52254 (Deny bare trait objects in in src/librustc_metadata)
- #52261 (Deny bare trait objects in in src/libpanic_unwind)
- #52265 (Deny bare trait objects in in src/librustc_codegen_utils)
Failed merges:
r? @ghost
Remove sync::Once::call_once 'static bound
See https://internals.rust-lang.org/t/sync-once-per-instance/7918 for more context.
Suggested r is @alexcrichton, the one who added the `'static` bound back in 2014. I don't want to officially r? though, if the system would even let me. I'd rather let the system choose the appropriate member since it knows more than I do.
`git blame` history for `sync::Once::call_once`'s signature:
- [std: Second pass stabilization of sync](f3a7ec7028) (Dec 2014)
```diff
- pub fn doit<F>(&'static self, f: F) where F: FnOnce() {
+ #[stable]
+ pub fn call_once<F>(&'static self, f: F) where F: FnOnce() {
```
- [libstd: use unboxed closures](cdbb3ca9b7) (Dec 2014)
```diff
- pub fn doit(&'static self, f: ||) {
+ pub fn doit<F>(&'static self, f: F) where F: FnOnce() {
```
- [std: Rewrite the `sync` module](71d4e77db8) (Nov 2014)
```diff
- pub fn doit(&self, f: ||) {
+ pub fn doit(&'static self, f: ||) {
```
> ```text
> The second layer is the layer provided by `std::sync` which is intended to be
> the thinnest possible layer on top of `sys_common` which is entirely safe to
> use. There are a few concerns which need to be addressed when making these
> system primitives safe:
>
> * Once used, the OS primitives can never be **moved**. This means that they
> essentially need to have a stable address. The static primitives use
> `&'static self` to enforce this, and the non-static primitives all use a
> `Box` to provide this guarantee.
> ```
The author of this diff is @alexcrichton. `sync::Once` now contains only a pointer to (privately hidden) `Waiter`s, which are all stack-allocated. The `'static` bound to `sync::Once` is thus unnecessary to guarantee that any OS primitives are non-relocatable.
As the `'static` bound is not required for `sync::Once`'s operation, removing it is strictly more useful. As an example, it allows attaching a one-time operation to instances rather than only to global singletons.
improve error message shown for unsafe operations
Add a short explanation saying why undefined behavior could arise. In particular, the error many people got for "creating a pointer to a packed field requires unsafe block" was not worded great -- it lead to people just adding the unsafe block without considering if what they are doing follows the rules.
I am not sure if a "note" is the right thing, but that was the easiest thing to add...
Inspired by @gnzlbg at https://github.com/rust-lang/rust/issues/46043#issuecomment-381544673
hygiene: Decouple transparencies from expansion IDs
And remove fallback to parent modules during resolution of names in scope.
This is a breaking change for users of unstable macros 2.0 (both procedural and declarative), code like this:
```rust
#![feature(decl_macro)]
macro m($S: ident) {
struct $S;
mod m {
type A = $S;
}
}
fn main() {
m!(S);
}
```
or equivalent
```rust
#![feature(decl_macro)]
macro m($S: ident) {
mod m {
type A = $S;
}
}
fn main() {
struct S;
m!(S);
}
```
stops working due to module boundaries being properly enforced.
For proc macro derives this is still reported as a compatibility warning to give `actix_derive`, `diesel_derives` and `palette_derive` time to fix their issues.
Fixes https://github.com/rust-lang/rust/issues/50504 in accordance with [this comment](https://github.com/rust-lang/rust/issues/50504#issuecomment-399764767).
Infinite loop detection for const evaluation
Resolves#50637.
An `EvalContext` stores the transient state (stack, heap, etc.) of the MIRI virtual machine while it executing code. As long as MIRI only executes pure functions, we can detect if a program is in a state where it will never terminate by periodically taking a "snapshot" of this transient state and comparing it to previous ones. If any two states are exactly equal, the machine must be in an infinite loop.
Instead of fully cloning a snapshot every time the detector is run, we store a snapshot's hash. Only when a hash collision occurs do we fully clone the interpreter state. Future snapshots which cause a collision will be compared against this clone, causing the interpreter to abort if they are equal.
At the moment, snapshots are not taken until MIRI has progressed a certain amount. After this threshold, snapshots are taken every `DETECTOR_SNAPSHOT_PERIOD` steps. This means that an infinite loop with period `P` will be detected after a maximum of `2 * P * DETECTOR_SNAPSHOT_PERIOD` interpreter steps. The factor of 2 arises because we only clone a snapshot after it causes a hash collision.
