Test rustc's automatic parenthesis insertion

[dtolnay]

Using the same technique as #1787, but on rustc expressions instead of syn.

This reveals numerous parenthesization false negatives in rustc_ast_pretty's algorithm and other bugs. A selection of examples:

FAIL tests/rust/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
BEFORE:
for expr in expr_finder.clones {
    if let hir::ExprKind::MethodCall(_, rcvr, _, span) = expr.kind
        && let Some(rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id)
        && let Some(ty) = typeck_results.node_type_opt(expr.hir_id)
        && rcvr_ty == ty
        && let ty::Ref (_, inner, _) = rcvr_ty.kind()
        && let inner = inner.peel_refs()
        && (Holds { ty: inner }).visit_ty(local_ty).is_break()
        && let None = self.infcx.type_implements_trait_shallow(clone, inner, self.param_env)
    {
        err.span_label(
            span,
            format!("this call doesn't do anything, the result is still `{rcvr_ty}` because `{inner}` doesn't implement `Clone`"),
        );
        types_to_constrain.insert(inner);
    }
}
AFTER:
for expr in expr_finder.clones {
    if (let hir::ExprKind::MethodCall(_, rcvr, _, span) = expr.kind &&
                                        let Some(rcvr_ty) =
                                            typeck_results.node_type_opt(rcvr.hir_id) &&
                                    let Some(ty) = typeck_results.node_type_opt(expr.hir_id) &&
                                rcvr_ty == ty && let ty::Ref(_, inner, _) = rcvr_ty.kind()
                        && let inner = inner.peel_refs() &&
                    Holds { ty: inner }.visit_ty(local_ty).is_break() &&
                let None =
                    self.infcx.type_implements_trait_shallow(clone, inner,
                        self.param_env)) {
            err.span_label(span,
                format!("this call doesn't do anything, the result is still `{rcvr_ty}` \
                             because `{inner}` doesn't implement `Clone`",));
            types_to_constrain.insert(inner);
        }
}

FAIL tests/rust/tests/ui/issues/issue-39548.rs
BEFORE:
((1 < 2) == false) as usize
AFTER:
(1 < 2 == false) as usize

FAIL tests/rust/tests/pretty/ast-stmt-expr-attr.rs
BEFORE:
(#[attr] foo).bar
AFTER:
#[attr] foo.bar

FAIL tests/rust/tests/pretty/ast-stmt-expr-attr.rs
BEFORE:
(#[attr] foo).0
AFTER:
#[attr] foo.0

FAIL tests/rust/tests/pretty/ast-stmt-expr-attr.rs
BEFORE:
(#[attr] foo) [bar]
AFTER:
#[attr] foo[bar]

FAIL tests/rust/src/tools/rust-analyzer/crates/parser/test_data/parser/inline/ok/let_expr.rs
BEFORE:
while 1 == 5 && (let None = None) {}
AFTER:
while 1 == 5 && let None = None {}

FAIL tests/rust/tests/pretty/stmt_expr_attributes.rs
BEFORE:
(#[rustc_dummy] s).data
AFTER:
#[rustc_dummy] s.data

FAIL tests/rust/tests/pretty/stmt_expr_attributes.rs
BEFORE:
(#[rustc_dummy] t).0
AFTER:
#[rustc_dummy] t.0

FAIL tests/rust/tests/pretty/stmt_expr_attributes.rs
BEFORE:
(#[rustc_dummy] v) [0]
AFTER:
#[rustc_dummy] v[0]

FAIL tests/rust/compiler/rustc_expand/src/proc_macro_server.rs
BEFORE:
if start > u32::MAX as usize
    || end > u32::MAX as usize
    || (u32::MAX - start as u32) < span.lo().to_u32()
    || (u32::MAX - end as u32) < span.lo().to_u32()
    || start >= end
    || end > length
{
    return None;
}
AFTER:
if start > u32::MAX as usize || end > u32::MAX as usize ||
                        u32::MAX - start as u32 < span.lo().to_u32() ||
                    u32::MAX - end as u32 < span.lo().to_u32() || start >= end
            || end > length {
        return None;
    }

FAIL tests/rust/src/tools/clippy/tests/ui/bool_comparison.rs
BEFORE:
((1 < 2) == false) as usize
AFTER:
(1 < 2 == false) as usize

FAIL tests/rust/src/tools/clippy/tests/ui/bool_comparison.rs
BEFORE:
((1 < 2) == !m!(func)) as usize
AFTER:
(1 < 2 == !m!(func)) as usize

FAIL tests/rust/tests/ui/lint/unused/issue-90807-unused-paren.rs
BEFORE:
for _ in (1..{ 2 }) {}
AFTER:
for _ in 1..{ 2 } {}

FAIL tests/rust/src/tools/rust-analyzer/crates/syntax/test_data/parser/validation/invalid_let_expr.rs
BEFORE:
if true { (let _ = None) }
AFTER:
if true { let _ = None }

FAIL tests/rust/src/tools/rust-analyzer/crates/syntax/test_data/parser/validation/invalid_let_expr.rs
BEFORE:
if true && (let _ = None) {
    (let _ = None);
    while let _ = None {
        match None {
            _ if let _ = None => {
                let _ = None;
            }
        }
    }
}
AFTER:
if true && let _ = None {
        let _ = None;
        while let _ = None {
            match None { _ if let _ = None => { let _ = None; } }
        }
    }

FAIL tests/rust/tests/ui/attrs-resolution.rs
BEFORE:
match foo_struct {
    FooStruct { #[rustfmt::skip] bar } => {}
}
AFTER:
match foo_struct { FooStruct { bar } => {} }