swc_ecma_transforms_react/pure_annotations/
mod.rs

1use rustc_hash::FxHashMap;
2use swc_atoms::Atom;
3use swc_common::{comments::Comments, Span};
4use swc_ecma_ast::*;
5use swc_ecma_visit::{noop_visit_mut_type, visit_mut_pass, VisitMut, VisitMutWith};
6
7#[cfg(test)]
8mod tests;
9
10/// A pass to add a /*#__PURE__#/ annotation to calls to known pure calls.
11///
12/// This pass adds a /*#__PURE__#/ annotation to calls to known pure top-level
13/// React methods, so that terser and other minifiers can safely remove them
14/// during dead code elimination.
15/// See https://reactjs.org/docs/react-api.html
16pub fn pure_annotations<C>(comments: Option<C>) -> impl Pass
17where
18    C: Comments,
19{
20    visit_mut_pass(PureAnnotations {
21        imports: Default::default(),
22        comments,
23    })
24}
25
26struct PureAnnotations<C>
27where
28    C: Comments,
29{
30    imports: FxHashMap<Id, (Atom, Atom)>,
31    comments: Option<C>,
32}
33
34impl<C> VisitMut for PureAnnotations<C>
35where
36    C: Comments,
37{
38    noop_visit_mut_type!();
39
40    fn visit_mut_module(&mut self, module: &mut Module) {
41        // Pass 1: collect imports
42        for item in &module.body {
43            if let ModuleItem::ModuleDecl(ModuleDecl::Import(import)) = item {
44                let src_str = &*import.src.value;
45                if src_str != "react" && src_str != "react-dom" {
46                    continue;
47                }
48
49                for specifier in &import.specifiers {
50                    let src = import.src.value.clone();
51                    match specifier {
52                        ImportSpecifier::Named(named) => {
53                            let imported = match &named.imported {
54                                Some(ModuleExportName::Ident(imported)) => imported.sym.clone(),
55                                Some(ModuleExportName::Str(..)) => named.local.sym.clone(),
56                                None => named.local.sym.clone(),
57                            };
58                            self.imports.insert(named.local.to_id(), (src, imported));
59                        }
60                        ImportSpecifier::Default(default) => {
61                            self.imports
62                                .insert(default.local.to_id(), (src, "default".into()));
63                        }
64                        ImportSpecifier::Namespace(ns) => {
65                            self.imports.insert(ns.local.to_id(), (src, "*".into()));
66                        }
67                    }
68                }
69            }
70        }
71
72        if self.imports.is_empty() {
73            return;
74        }
75
76        // Pass 2: add pure annotations.
77        module.visit_mut_children_with(self);
78    }
79
80    fn visit_mut_call_expr(&mut self, call: &mut CallExpr) {
81        let is_react_call = match &call.callee {
82            Callee::Expr(expr) => match &**expr {
83                Expr::Ident(ident) => {
84                    if let Some((src, specifier)) = self.imports.get(&ident.to_id()) {
85                        is_pure(src, specifier)
86                    } else {
87                        false
88                    }
89                }
90                Expr::Member(member) => match &*member.obj {
91                    Expr::Ident(ident) => {
92                        if let Some((src, specifier)) = self.imports.get(&ident.to_id()) {
93                            if &**specifier == "default" || &**specifier == "*" {
94                                match &member.prop {
95                                    MemberProp::Ident(ident) => is_pure(src, &ident.sym),
96                                    _ => false,
97                                }
98                            } else {
99                                false
100                            }
101                        } else {
102                            false
103                        }
104                    }
105                    _ => false,
106                },
107                _ => false,
108            },
109            _ => false,
110        };
111
112        if is_react_call {
113            if let Some(comments) = &self.comments {
114                if call.span.lo.is_dummy() {
115                    call.span.lo = Span::dummy_with_cmt().lo;
116                }
117
118                comments.add_pure_comment(call.span.lo);
119            }
120        }
121
122        call.visit_mut_children_with(self);
123    }
124}
125
126fn is_pure(src: &Atom, specifier: &Atom) -> bool {
127    match &**src {
128        "react" => matches!(
129            &**specifier,
130            "cloneElement"
131                | "createContext"
132                | "createElement"
133                | "createFactory"
134                | "createRef"
135                | "forwardRef"
136                | "isValidElement"
137                | "memo"
138                | "lazy"
139        ),
140        "react-dom" => matches!(&**specifier, "createPortal"),
141        _ => false,
142    }
143}
swc_ecma_transforms_react/pure_annotations/mod.rs

swc_ecma_transforms_react/pure_annotations/
mod.rs
