compiler/rustc_ast/src/util/classify.rs

//! Routines the parser uses to classify AST nodes

// Predicates on exprs and stmts that the pretty-printer and parser use

use crate::ast;

/// Does this expression require a semicolon to be treated
/// as a statement? The negation of this: 'can this expression
/// be used as a statement without a semicolon' -- is used
/// as an early-bail-out in the parser so that, for instance,
///     if true {...} else {...}
///      |x| 5
/// isn't parsed as (if true {...} else {...} | x) | 5
pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
    !matches!(
        e.kind,
        ast::ExprKind::If(..)
            | ast::ExprKind::Match(..)
            | ast::ExprKind::Block(..)
            | ast::ExprKind::While(..)
            | ast::ExprKind::Loop(..)
            | ast::ExprKind::ForLoop(..)
            | ast::ExprKind::TryBlock(..)
    )
}

/// If an expression ends with `}`, returns the innermost expression ending in the `}`
pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<&ast::Expr> {
    use ast::ExprKind::*;

    loop {
        match &expr.kind {
            AddrOf(_, _, e)
            | Assign(_, e, _)
            | AssignOp(_, _, e)
            | Binary(_, _, e)
            | Box(e)
            | Break(_, Some(e))
            | Closure(.., e, _)
            | Let(_, e, _)
            | Range(_, Some(e), _)
            | Ret(Some(e))
            | Unary(_, e)
            | Yield(Some(e)) => {
                expr = e;
            }
            Async(..) | Block(..) | ForLoop(..) | If(..) | Loop(..) | Match(..) | Struct(..)
            | TryBlock(..) | While(..) => break Some(expr),
            _ => break None,
        }
    }
}