deno/cli/tools/bundle/transform.rs

// Copyright 2018-2025 the Deno authors. MIT license.

use deno_ast::swc;
use deno_ast::swc::ast::Bool;
use deno_ast::swc::ecma_visit::VisitMut;
use deno_ast::swc::ecma_visit::VisitMutWith;

pub struct BundleImportMetaMainTransform {
  is_entrypoint: bool,
}

impl BundleImportMetaMainTransform {
  pub fn new(is_entrypoint: bool) -> Self {
    Self { is_entrypoint }
  }
}

impl VisitMut for BundleImportMetaMainTransform {
  fn visit_mut_expr(&mut self, node: &mut swc::ast::Expr) {
    // if entrypoint to bundle:
    //   import.meta.main => import.meta.main
    // else:
    //   import.meta.main => false
    if let swc::ast::Expr::Member(member) = node {
      if let swc::ast::Expr::MetaProp(meta_prop) = &mut *member.obj {
        if meta_prop.kind == swc::ast::MetaPropKind::ImportMeta
          && member.prop.is_ident_with("main")
        {
          if self.is_entrypoint {
            return;
          } else {
            let span = member.span;
            *node = swc::ast::Expr::Lit(swc::ast::Lit::Bool(Bool {
              span,
              value: false,
            }));
            return;
          }
        }
      }
    }
    node.visit_mut_children_with(self);
  }
}