Rollup merge of #134833 - dtolnay:leftmostwithdot, r=compiler-errors

Skip parenthesis if `.` makes statement boundary unambiguous

There is a rule in the parser that statements and match-arms never end in front of a `.` or `?` token (except when the `.` is really `..` or `..=` or `...`). So some of the leading subexpressions that need parentheses inserted when followed by some other operator like `-` or `+`, do not need parentheses when followed by `.` or `?`.

Example:

```rust
fn main() {
    loop {}.to_string() + "";
    match () {
        _ => loop {}.to_string() + "",
    };
}
```

`-Zunpretty=expanded` before:

```console
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
fn main() {
    (loop {}).to_string() + "";
    match () { _ => (loop {}).to_string() + "", };
}
```

After:

```console
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
fn main() {
    loop {}.to_string() + "";
    match () { _ => loop {}.to_string() + "", };
}
```

0 files changed, 0 insertions, 0 deletions