swc_ecma_minifier/compress/optimize/
rest_params.rs

1use swc_ecma_ast::*;
2
3use super::Optimizer;
4
5/// Methods related to rest parameter optimization.
6impl Optimizer<'_> {
7    /// Removes unused rest parameters from functions.
8    ///
9    /// Example:
10    /// ```js
11    /// function f(a, ...b) {
12    ///     console.log(a);
13    /// }
14    /// ```
15    /// =>
16    /// ```js
17    /// function f(a) {
18    ///     console.log(a);
19    /// }
20    /// ```
21    pub(super) fn drop_unused_rest_params(&mut self, f: &mut Function) {
22        if !self.options.arguments && !self.options.unused {
23            return;
24        }
25
26        // Don't optimize if there's no rest parameter
27        if f.params.is_empty() {
28            return;
29        }
30
31        let last_param = match f.params.last() {
32            Some(p) => p,
33            None => return,
34        };
35
36        // Check if the last parameter is a rest parameter
37        let rest_pat = match &last_param.pat {
38            Pat::Rest(rest) => rest,
39            _ => return,
40        };
41
42        // Get the identifier of the rest parameter
43        let rest_id = match &*rest_pat.arg {
44            Pat::Ident(BindingIdent { id, .. }) => id.to_id(),
45            _ => return,
46        };
47
48        // Check if the rest parameter is used using ProgramData
49        if let Some(usage) = self.data.vars.get(&rest_id) {
50            // If the parameter is not referenced, we can remove it
51            if usage.ref_count == 0 {
52                self.changed = true;
53                report_change!("rest_params: Removing unused rest parameter");
54                f.params.pop();
55            }
56        }
57    }
58}
swc_ecma_minifier/compress/optimize/rest_params.rs

swc_ecma_minifier/compress/optimize/
rest_params.rs
