1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

use crate::util::{contains_this_expr, ExprFactory};
use swc_common::{Spanned, DUMMY_SP};
use swc_ecma_ast::*;
use swc_ecma_utils::quote_ident;
use swc_ecma_visit::{Fold, FoldWith, Node, Visit, VisitWith};

/// Compile ES2015 arrow functions to ES5
///
///# Example
///
///## In
/// ```js
/// var a = () => {};
/// var a = (b) => b;ß
///
/// const double = [1,2,3].map((num) => num * 2);
/// console.log(double); // [2,4,6]
///
/// var bob = {
///   _name: "Bob",
///   _friends: ["Sally", "Tom"],
///   printFriends() {
///     this._friends.forEach(f =>
///       console.log(this._name + " knows " + f));
///   }
/// };
/// console.log(bob.printFriends());
/// ```
///
///## Out
///```js
/// var a = function () {};
/// var a = function (b) {
///   return b;
/// };
///
/// const double = [1, 2, 3].map(function (num) {
///   return num * 2;
/// });
/// console.log(double); // [2,4,6]
///
/// var bob = {
///   _name: "Bob",
///   _friends: ["Sally", "Tom"],
///   printFriends() {
///     var _this = this;
///
///     this._friends.forEach(function (f) {
///       return console.log(_this._name + " knows " + f);
///     });
///   }
/// };
/// console.log(bob.printFriends());
/// ```
pub fn arrow() -> impl Fold {
    Arrow
}

struct Arrow;

noop_fold_type!(Arrow);

impl Fold for Arrow {
    fn fold_expr(&mut self, e: Expr) -> Expr {
        // fast path
        if !contains_arrow_expr(&e) {
            return e;
        }

        let e = validate!(e);
        let e = e.fold_children_with(self);

        match e {
            Expr::Arrow(ArrowExpr {
                span,
                params,
                body,
                is_async,
                is_generator,
                type_params,
                return_type,
            }) => {
                let used_this = contains_this_expr(&body);

                let fn_expr = Expr::Fn(FnExpr {
                    ident: None,
                    function: Function {
                        decorators: vec![],
                        span,
                        params: params
                            .into_iter()
                            .map(|pat| Param {
                                span: DUMMY_SP,
                                decorators: Default::default(),
                                pat,
                            })
                            .collect(),
                        is_async,
                        is_generator,
                        body: Some(match body {
                            BlockStmtOrExpr::BlockStmt(block) => block,
                            BlockStmtOrExpr::Expr(expr) => BlockStmt {
                                span: DUMMY_SP,
                                stmts: vec![Stmt::Return(ReturnStmt {
                                    span: expr.span(),
                                    arg: Some(expr),
                                })],
                            },
                        }),
                        type_params,
                        return_type,
                    },
                });

                if !used_this {
                    return fn_expr;
                }

                Expr::Call(CallExpr {
                    span,
                    callee: fn_expr.make_member(quote_ident!("bind")).as_callee(),
                    args: vec![ThisExpr { span: DUMMY_SP }.as_arg()],
                    type_args: Default::default(),
                })
            }
            _ => e,
        }
    }
}

fn contains_arrow_expr<N>(node: &N) -> bool
where
    N: VisitWith<ArrowVisitor>,
{
    let mut v = ArrowVisitor { found: false };
    node.visit_with(&Invalid { span: DUMMY_SP } as _, &mut v);
    v.found
}

struct ArrowVisitor {
    found: bool,
}
impl Visit for ArrowVisitor {
    fn visit_arrow_expr(&mut self, _: &ArrowExpr, _: &dyn Node) {
        self.found = true;
    }
}