swc_ecma_transforms_optimization/
const_modules.rs

use std::{collections::HashMap, sync::Arc};

use dashmap::DashMap;
use once_cell::sync::Lazy;
use rustc_hash::FxHashMap;
use swc_atoms::JsWord;
use swc_common::{errors::HANDLER, sync::Lrc, util::move_map::MoveMap, FileName, SourceMap};
use swc_ecma_ast::*;
use swc_ecma_parser::parse_file_as_expr;
use swc_ecma_utils::drop_span;
use swc_ecma_visit::{noop_fold_type, Fold, FoldWith};

pub fn const_modules(
    cm: Lrc<SourceMap>,
    globals: FxHashMap<JsWord, FxHashMap<JsWord, String>>,
) -> impl Fold {
    ConstModules {
        globals: globals
            .into_iter()
            .map(|(src, map)| {
                let map = map
                    .into_iter()
                    .map(|(key, value)| {
                        let value = parse_option(&cm, &key, value);

                        (key, value)
                    })
                    .collect();

                (src, map)
            })
            .collect(),
        scope: Default::default(),
    }
}

fn parse_option(cm: &SourceMap, name: &str, src: String) -> Arc<Expr> {
    static CACHE: Lazy<DashMap<String, Arc<Expr>, ahash::RandomState>> =
        Lazy::new(DashMap::default);

    let fm = cm.new_source_file(FileName::Custom(format!("<const-module-{}.js>", name)), src);
    if let Some(expr) = CACHE.get(&**fm.src) {
        return expr.clone();
    }

    let expr = parse_file_as_expr(
        &fm,
        Default::default(),
        Default::default(),
        None,
        &mut vec![],
    )
    .map_err(|e| {
        if HANDLER.is_set() {
            HANDLER.with(|h| e.into_diagnostic(h).emit())
        }
    })
    .map(drop_span)
    .unwrap_or_else(|()| {
        panic!(
            "failed to parse jsx option {}: '{}' is not an expression",
            name, fm.src,
        )
    });

    let expr = Arc::new(*expr);

    CACHE.insert((*fm.src).clone(), expr.clone());

    expr
}

struct ConstModules {
    globals: HashMap<JsWord, HashMap<JsWord, Arc<Expr>>>,
    scope: Scope,
}

#[derive(Default)]
struct Scope {
    imported: HashMap<JsWord, Arc<Expr>>,
}

/// TODO: VisitMut
impl Fold for ConstModules {
    noop_fold_type!();

    fn fold_module_items(&mut self, items: Vec<ModuleItem>) -> Vec<ModuleItem> {
        items.move_flat_map(|item| match item {
            ModuleItem::ModuleDecl(ModuleDecl::Import(import)) => {
                let entry = self.globals.get(&import.src.value);

                if let Some(entry) = entry {
                    for s in &import.specifiers {
                        let i = match *s {
                            ImportSpecifier::Named(ref s) => &s.local,
                            ImportSpecifier::Namespace(..) => unimplemented!(
                                "const modules does not support namespace import yet"
                            ),
                            ImportSpecifier::Default(..) => {
                                panic!("const_modules does not support default import")
                            }
                        };
                        let value = entry.get(&i.sym).cloned().unwrap_or_else(|| {
                            panic!(
                                "const_modules: {} does not contain flags named {}",
                                import.src.value, i.sym
                            )
                        });
                        self.scope.imported.insert(i.sym.clone(), value);
                    }

                    None
                } else {
                    Some(ModuleItem::ModuleDecl(ModuleDecl::Import(import)))
                }
            }
            _ => Some(item.fold_with(self)),
        })
    }

    fn fold_expr(&mut self, expr: Expr) -> Expr {
        let expr = match expr {
            Expr::Member(expr) => Expr::Member(MemberExpr {
                obj: expr.obj.fold_with(self),
                prop: if let MemberProp::Computed(c) = expr.prop {
                    MemberProp::Computed(c.fold_with(self))
                } else {
                    expr.prop
                },
                ..expr
            }),

            Expr::SuperProp(expr) => Expr::SuperProp(SuperPropExpr {
                prop: if let SuperProp::Computed(c) = expr.prop {
                    SuperProp::Computed(c.fold_with(self))
                } else {
                    expr.prop
                },
                ..expr
            }),
            _ => expr.fold_children_with(self),
        };
        match expr {
            Expr::Ident(Ident { ref sym, .. }) => {
                // It's ok because we don't recurse into member expressions.
                if let Some(value) = self.scope.imported.get(sym) {
                    (**value).clone()
                } else {
                    expr
                }
            }
            _ => expr,
        }
    }
}
swc_ecma_transforms_optimization/const_modules.rs

swc_ecma_transforms_optimization/
const_modules.rs
