Eliminate ZST allocations in `Box` and `Vec`
This PR fixes 2 issues with `Box` and `RawVec` related to ZST allocations. Specifically, the `Allocator` trait requires that:
- If you allocate a zero-sized layout then you must later deallocate it, otherwise the allocator may leak memory.
- You cannot pass a ZST pointer to the allocator that you haven't previously allocated.
These restrictions exist because an allocator implementation is allowed to allocate non-zero amounts of memory for a zero-sized allocation. For example, `malloc` in libc does this.
Currently, ZSTs are handled differently in `Box` and `Vec`:
- `Vec` never allocates when `T` is a ZST or if the vector capacity is 0.
- `Box` just blindly passes everything on to the allocator, including ZSTs.
This causes problems due to the free conversions between `Box<[T]>` and `Vec<T>`, specifically that ZST allocations could get leaked or a dangling pointer could be passed to `deallocate`.
This PR fixes this by changing `Box` to not allocate for zero-sized values and slices. It also fixes a bug in `RawVec::shrink` where shrinking to a size of zero did not actually free the backing memory.
Add jump to doc
I'm using the source code pages of the compiler quite a lot, but one thing missing is the possibility to jump back from the source code to the item documentation. Since I also got a few others complaining about it, I think it's fine to add it since this option is nightly only.
This PR adds a link to jump back to item's documentation on the item definition (so on `Bar` in `struct Bar {... }`, as described in the unofficial [RFC](https://github.com/GuillaumeGomez/rfcs/blob/rustdoc-jump-to-definition/text/000-rustdoc-jump-to-definition.md)).
r? ````@notriddle````
Test simd-wide-sum for codegen error
This adds the necessary test infrastructure to "build-pass" codegen tests, for the purpose of doing that for a single revision of a codegen test. When mir-opts are tested, the output may vary from the usual, and maybe for positive reasons... but we don't necessarily want to output such bad LLVMIR that LLVM starts crashing on it.
Currently when enabling MIR opts at higher levels this LLVMIR is still emitted, but it was previously disabled for getting in mir-opt's way and as this new revision without `// [mir-opt3]build-pass` would make it more likely to, I would like to not see the testing for the actual results regress again just because it was bundled with an ICE check as well.
This fixes https://github.com/rust-lang/rust/issues/98016
Implement selection for `Unsize` for better coercion behavior
In order for much of coercion to succeed, we need to be able to deal with partial ambiguity of `Unsize` traits during selection. However, I pessimistically implemented selection in the new trait solver to just bail out with ambiguity if it was a built-in impl:
9227ff28af/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs (L126)
This implements a proper "rematch" procedure for dealing with built-in `Unsize` goals, so that even if the goal is ambiguous, we are able to get nested obligations which are used in the coercion selection-like loop:
9227ff28af/compiler/rustc_hir_typeck/src/coercion.rs (L702)
Second commit just moves a `resolve_vars_if_possible` call to fix a bug where we weren't detecting a trait upcasting to occur.
r? ``@lcnr``
...which seems not to be available on some platforms.
Or maybe it is under a different name but I don't want to deal with that
Instead, use two u64s. This isn't exactly the same, but we already have
some coverage of the packed u128 case in another test, so it's not
essential to have it here.
(re-)tighten sourceinfo span of adjustments in MIR
Diagnostics rely on the spans of MIR statements being (approximately) correct in order to give suggestions relative to that span (i.e. `shrink_to_hi` and `shrink_to_lo`).
I discovered that we're *intentionally* lowering THIR exprs with their parent expr's span if they come from adjustments that are due to a parent expression. While I understand why that may be desirable to demonstrate the relationship of an adjustment and the expression that requires it, it leads to
1. very verbose borrowck output
2. incorrect spans for suggestions
Some diagnostics get around that by giving suggestions relative to other spans we've collected during MIR lowering, such as the span of the method's identifier (e.g. `name` in `.name()`), but this doesn't work too well when things come from desugaring.
I assume it also has lead to numerous tweaks and complications to diagnostics code down the road, which this PR doesn't necessarily aim to fix but may open the gates to fixing later... The last three commits are simplifications due to the fact that we can assume that the move span actually points to what is being moved (and a test).
This regressed in #89110, which was debated somewhat in #90286. cc `@Aaron1011` who originally made this change.
r? diagnostics
Fixes#113547Fixes#111016
Previously, forgetting to call `interface::set_thread_safe_mode` would cause the following ICE:
```
thread 'rustc' panicked at 'uninitialized dyn_thread_safe mode!', /rustc/dfe0683138de0959b6ab6a039b54d9347f6a6355/compiler/rustc_data_structures/src/sync.rs:74:18
```
This calls `set_thread_safe_mode` in `interface::run_compiler` to avoid requiring it in the caller.
Fixes `tests/run-make-fulldeps/issue-19371` when parallel-compiler is enabled.
Rollup of 4 pull requests
Successful merges:
- #112717 (Implement a few more rvalue translation to smir)
- #113310 (Don't suggest `impl Trait` in path position)
- #113497 (Support explicit 32-bit MIPS ABI for the synthetic object)
- #113560 (Lint against misplaced where-clauses on associated types in traits)
r? `@ghost`
`@rustbot` modify labels: rollup
Lint against misplaced where-clauses on associated types in traits
Extends the scope of the lint `deprecated_where_clause_location` (#89122) from associated types in impls to associated types in any location (impl or trait). This is only relevant for `#![feature(associated_type_defaults)]`. Previously we didn't warn on the following code for example:
```rs
#![feature(associated_type_defaults)]
trait Trait { type Assoc where u32: Copy = (); }
```
Personally I would've preferred to emit a *hard* error here instead of a lint warning since the feature is unstable but unfortunately we are constrained by back compat as associated type defaults won't necessarily trigger the feature-gate error if they are inside of a macro call (since they use a post-expansion feature-gate due to historical reasons, see also #66004).
I've renamed and moved related preexisting tests: 1. They test AST validation passes not the parser & thus shouldn't live in `parser/` (historical reasons?). 2. One test file was named after type aliases even though it tests assoc tys.
`@rustbot` label A-lint
Structurally resolve in pattern matching when peeling refs in new solver
Let me know if you want me to commit the minimized test:
```rust
fn test() {}
fn test2() {}
fn main() {
let tests: &[(_, fn())] = &[
("test", test),
("test2", test2),
];
for (a, b) in tests {
todo!();
}
}
```
In that test above, the match scrutinee is `<std::vec::Iter<(&'static str, fn())> as Iterator>::Item`, which we cannot peel the refs from.
We also need to structurally resolve in the loop, since structural resolve is inherently shallow. I haven't come up with a test where this matters, but I can if you care.
Also, I removed two other calls to `resolve_vars_with_obligations` in diagnostics code that I'm pretty convinced are not useful.
r? `@lcnr`
Enable coinduction support for Safe Transmute
This patch adds the `#[rustc_coinductive]` annotation to `BikeshedIntrinsicFrom`, so that it's possible to compute transmutability for recursive types.
## Motivation
Safe Transmute currently already supports references (#110662). However, if a type is implemented recursively, it leads to an infinite loop when we try to check if transmutation is safe.
A couple simple examples that one might want to write, that are currently not possible to check transmutability for:
```rs
#[repr(C)] struct A(&'static B);
#[repr(C)] struct B(&'static A);
```
```rs
#[repr(C)]
enum IList<'a> { Nil, Cons(isize, &'a IList<'a>) }
#[repr(C)]
enum UList<'a> { Nil, Cons(usize, &'a UList<'a>) }
```
Previously, `@jswrenn` was considering writing a co-inductive solver from scratch, just for the `rustc_tranmsute` crate. Later on as I started working on Safe Transmute myself, I came across the `#[rustc_coinductive]` annotation, which is currently only being used for the `Sized` trait. Leveraging this trait actually solved the problem entirely, and it saves a lot of duplicate work that would have had to happen in `rustc_transmute`.
Uplift `clippy::fn_null_check` lint
This PR aims at uplifting the `clippy::fn_null_check` lint into rustc.
## `incorrect_fn_null_checks`
(warn-by-default)
The `incorrect_fn_null_checks` lint checks for expression that checks if a function pointer is null.
### Example
```rust
let fn_ptr: fn() = /* somehow obtained nullable function pointer */
if (fn_ptr as *const ()).is_null() { /* ... */ }
```
### Explanation
Function pointers are assumed to be non-null, checking for their nullity is incorrect.
-----
Mostly followed the instructions for uplifting a clippy lint described here: https://github.com/rust-lang/rust/pull/99696#pullrequestreview-1134072751
`@rustbot` label: +I-lang-nominated
r? compiler
