The AST pretty printer was dropping parentheses around or-patterns
when they appeared inside `@` bindings, `&` references, or `box`
patterns. For example:
- `v @ (1 | 2 | 3)` was printed as `v @ 1 | 2 | 3`
- `&(1 | 2 | 3)` was printed as `&1 | 2 | 3`
- `box (1 | 2 | 3)` was printed as `box 1 | 2 | 3`
Since `|` has the lowest precedence among pattern operators, all of
these are parsed incorrectly without parentheses — e.g. `v @ 1 | 2 | 3`
becomes `(v @ 1) | 2 | 3`, binding `v` only to the first alternative.
This caused E0408 ("variable not bound in all patterns") when the
expanded output was fed back to the compiler, affecting crates like
html5ever and wgpu-core that use macros expanding to or-patterns
after `@`.
The fix adds a `print_pat_paren_if_or` helper that wraps `PatKind::Or`
subpatterns in parentheses, and uses it in the `@`, `&`, and `box`
printing arms. This is similar in spirit to the existing `FixupContext`
parenthesization approach used for expression printing.
Signed-off-by: Andrew V. Teylu <andrew.teylu@vector.com>
Andrew V. Teylu