Fix bugs in macro-expanded statement parsing
Fixes#34543.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m { () => {
println!("") println!("")
//^ Semicolons are now required on macro-expanded non-braced macro invocations
//| in statement positions.
let x = 0
//^ Semicolons are now required on macro-expanded `let` statements
//| that are followed by more statements, so this would break.
let y = 0 //< (this would still be allowed to reduce breakage in the wild)
}
fn main() { m!() }
```
r? @eddyb
```rust
macro_rules! m { () => { let x = 1; x } }
macro_rules! n { () => {
m!() //< This can now expand into statements
}}
fn main() { n!(); }
```
and revert needless fallout fixes.
Fix expansion performance regression
**syntax-[breaking-change] cc #31645**
This fixes#34630 by reverting commit 5bf7970 of PR #33943, which landed in #34424.
By removing the `Rc<_>` wrapping around `Delimited` and `SequenceRepetition` in `TokenTree`, 5bf7970 made cloning `TokenTree`s more expensive. While this had no measurable performance impact on the compiler's crates, it caused an order of magnitude performance regression on some macro-heavy code in the wild. I believe this is due to clones of `TokenTree`s in `macro_parser.rs` and/or `macro_rules.rs`.
r? @nrc
Support `cfg_attr` on `path` attributes
Fixes#25544.
This is technically a [breaking-change]. For example, the following would break:
```rust
mod foo; // Suppose `foo.rs` existed in the appropriate location
```
Identify when documetation comments have been missplaced in the
following places:
* After a struct element:
```rust
// file.rs:
struct X {
a: u8 /** document a */,
}
```
```bash
$ rustc file.rs
file.rs:2:11: 2:28 error: found documentation comment that doesn't
document anything
file.rs:2 a: u8 /** document a */,
^~~~~~~~~~~~~~~~~
file.rs:2:11: 2:28 help: doc comments must come before what they document,
maybe a comment was intended with `//`?
```
* As the last line of a struct:
```rust
// file.rs:
struct X {
a: u8,
/// incorrect documentation
}
```
```bash
$ rustc file.rs
file.rs:3:5: 3:27 error: found a documentation comment that doesn't
document anything
file.rs:3 /// incorrect documentation
^~~~~~~~~~~~~~~~~~~~~~
file.rs:3:5: 3:27 help: doc comments must come before what they document,
maybe a comment was intended with `//`?
```
* As the last line of a `fn`:
```rust
// file.rs:
fn main() {
let x = 1;
/// incorrect documentation
}
```
```bash
$ rustc file.rs
file.rs:3:5: 3:27 error: found a documentation comment that doesn't
document anything
file.rs:3 /// incorrect documentation
^~~~~~~~~~~~~~~~~~~~~~
file.rs:3:5: 3:27 help: doc comments must come before what they document,
maybe a comment was intended with `//`?
```
Fix#27429, #30322
This is a spiritual succesor to #34268/8531d581, in which we replaced a
number of matches of None to the unit value with `if let` conditionals
where it was judged that this made for clearer/simpler code (as would be
recommended by Manishearth/rust-clippy's `single_match` lint). The same
rationale applies to matches of None to the empty block.
Forbid type parameters and global paths in macro invocations
Fixes#28558.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m { () => { () } }
fn main() {
m::<T>!(); // Type parameters are no longer allowed in macro invocations
::m!(); // Global paths are no longer allowed in macro invocations
}
```
Any breakage can be fixed by removing the type parameters or the leading `::` (respectively).
r? @eddyb
