rust/src/libsyntax/parse/classify.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Routines the parser uses to classify AST nodes

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

use ast::{self, BlockCheckMode};

/// 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 {
    match e.node {
        ast::ExprKind::If(..) |
        ast::ExprKind::IfLet(..) |
        ast::ExprKind::Match(..) |
        ast::ExprKind::Block(_) |
        ast::ExprKind::While(..) |
        ast::ExprKind::WhileLet(..) |
        ast::ExprKind::Loop(..) |
        ast::ExprKind::ForLoop(..) => false,
        _ => true,
    }
}

pub fn expr_is_simple_block(e: &ast::Expr) -> bool {
    match e.node {
        ast::ExprKind::Block(ref block) => block.rules == BlockCheckMode::Default,
        _ => false,
    }
}

/// this statement requires a semicolon after it.
/// note that in one case (stmt_semi), we've already
/// seen the semicolon, and thus don't need another.
pub fn stmt_ends_with_semi(stmt: &ast::Stmt_) -> bool {
    match *stmt {
        ast::StmtDecl(ref d, _) => {
            match d.node {
                ast::DeclKind::Local(_) => true,
                ast::DeclKind::Item(_) => false,
            }
        }
        ast::StmtExpr(ref e, _) => expr_requires_semi_to_be_stmt(e),
        ast::StmtSemi(..) => false,
        ast::StmtMac(..) => false,
    }
}