ESLint rule to check for duplicated exported names.

index.js

// @ts-check

/** @type {import("eslint").Rule.RuleModule} */
const rule = {
  meta: {
    docs: {
      description: `You can export a type and a value with the same name in the same file, but that confuses refactoring tools.`,
    },
  },
  create(context) {
    return {
      Program(node) {
        // 1) find exported names
        if (node.type !== 'Program') return;

        const declarations = [];
        node.body.forEach((item) => {
          if (item.type !== 'ExportNamedDeclaration') return;
          if (!item.declaration) return;

          // for
          // - export type Foo = {};
          // - export function Foo(){};
          if ('id' in item.declaration) {
            declarations.push(item.declaration);
          }

          // for
          // - export const Foo = {};
          if ('declarations' in item.declaration) {
            item.declaration.declarations.forEach((declaration) => {
              if (declaration.id.type === 'Identifier') {
                declarations.push(declaration);
              }
            });
          }
        });

        // 2) report duplicates
        declarations.forEach((declaration) => {
          const foundDuplicate = declarations.some(
            (checkDeclaration) =>
              checkDeclaration !== declaration &&
              checkDeclaration.id.name === declaration.id.name
          );
          if (!foundDuplicate) return;

          context.report({
            node: declaration,
            message: `There is another export with the name ${declaration.id.name} in this file.`,
          });
        });
      },
    };
  },
};

module.exports = rule;