rustc: fix check_attr() for methods, closures and foreign functions
This fixes an issue that previously turned up for methods in https://github.com/rust-lang/rust/pull/69274, but also exists for closures and foreign function: `check_attr` does not call `codegen_fn_attrs()` for these types when it should, meaning that incorrectly used function attributes are not diagnosed without codegen.
The issue affects our UI tests, as they run with `--emit=metadata` by default, but as it turns out, this is not the only case: Function attributes are not checked on any dead code without this fix!
This makes the fix a **breaking change**. The following very silly Rust programs compiles fine on stable Rust when it should not, which is fixed by this PR.
```rust
fn main() {
#[target_feature(enable = "sse2")]
|| {};
}
```
I assume any real-world program which may trigger this issue would at least emit a dead code warning, but of course that is no guarantee that such code does not exist...
Fixes#70307
Increase verbosity when suggesting subtle code changes
Do not suggest changes that are actually quite small inline, to minimize the likelihood of confusion.
Fix#69243.
Optimize catch_unwind to match C++ try/catch
This refactors the implementation of catching unwinds to allow LLVM to inline the "try" closure directly into the happy path, avoiding indirection. This means that the catch_unwind implementation is (after this PR) zero-cost unless a panic is thrown.
https://rust.godbolt.org/z/cZcUSB is an example of the current codegen in a simple case. Notably, the codegen is *exactly the same* if `-Cpanic=abort` is passed, which is clearly not great.
This PR, on the other hand, generates the following assembly:
```asm
# -Cpanic=unwind:
push rbx
mov ebx,0x2a
call QWORD PTR [rip+0x1c53c] # <happy>
mov eax,ebx
pop rbx
ret
mov rdi,rax
call QWORD PTR [rip+0x1c537] # cleanup function call
call QWORD PTR [rip+0x1c539] # <unfortunate>
mov ebx,0xd
mov eax,ebx
pop rbx
ret
# -Cpanic=abort:
push rax
call QWORD PTR [rip+0x20a1] # <happy>
mov eax,0x2a
pop rcx
ret
```
Fixes#64224, and resolves#64222.
Towards unified `fn` grammar
Part of https://github.com/rust-lang/rust/pull/68728.
- Syntactically, `fn` items in `extern { ... }` blocks can now have bodies (`fn foo() { ... }` as opposed to `fn foo();`). As above, we use semantic restrictions instead.
- Syntactically, `fn` items in free contexts (directly in a file or a module) can now be without bodies (`fn foo();` as opposed to `fn foo() { ... }`. As above, we use semantic restrictions instead, including for non-ident parameter patterns.
- We move towards unifying the `fn` front matter; this is fully realized in https://github.com/rust-lang/rust/pull/68728.
r? @petrochenkov
Address inconsistency in using "is" with "declared here"
"is" was generally used for NLL diagnostics, but not other diagnostics. Using "is" makes the diagnostics sound more natural and readable, so it seems sensible to commit to them throughout.
r? @Centril
