migrate-default-exports-to-named-exports.js

/*
  This codemod migrates usage of default exports to named exports instead

  See migrate-default-exports-to-named-exports.test.js for before/after examples.
 */
export const parser = 'tsx';

const generateNamedExportDeclaration = (jscodeshift, inlineDefaultExport, filePath) => {
  const declarationType = inlineDefaultExport.node.declaration.type;
  if (declarationType === 'FunctionDeclaration' || declarationType === 'ClassDeclaration') {
    return jscodeshift.exportNamedDeclaration(inlineDefaultExport.node.declaration);
  }

  const dynamicExportName = filePath.split('/').pop().split('.')[0];
  const exportName = jscodeshift.identifier(dynamicExportName);

  return jscodeshift.exportNamedDeclaration(
    jscodeshift.variableDeclaration('const', [
      jscodeshift.variableDeclarator(exportName, inlineDefaultExport.node.declaration),
    ])
  );
};

function migrateDefaultExports(source, jscodeshift, filePath) {
  if (filePath.includes('.story.') || filePath.includes('.stories.')) {
    return;
  }

  // migrate inline default exports, giving them an export name of the filename
  source
    .find(jscodeshift.ExportDefaultDeclaration, (t) => t.declaration.type !== 'Identifier')
    .replaceWith((inlineDefaultExport) => generateNamedExportDeclaration(jscodeshift, inlineDefaultExport, filePath));

  // migrate default exports that just reference a variable
  source
    .find(jscodeshift.ExportDefaultDeclaration, { declaration: { type: 'Identifier' } })
    .forEach((defaultExport) => {
      const constThatWasBeingDefaultExported = defaultExport.value.declaration.name;
      const filter = { id: { name: constThatWasBeingDefaultExported } };

      // remove the old default export
      defaultExport.get().prune();

      // check if it's already being exported as a const
      if (source.find(jscodeshift.ExportNamedDeclaration, { declaration: { declarations: [filter] } }).length) {
        return;
      }

      // check if it's already being exported as a function or a class
      if (source.find(jscodeshift.ExportNamedDeclaration, { declaration: filter }).length) {
        return;
      }

      // update original declarations with export keyword
      const namedExportGenerator = (original) => jscodeshift.exportNamedDeclaration(original.node);
      source.find(jscodeshift.VariableDeclaration, { declarations: [filter] }).replaceWith(namedExportGenerator);
      source.find(jscodeshift.FunctionDeclaration, filter).replaceWith(namedExportGenerator);
    });
}

function migrateExportDefaultAsStatements(source, jscodeshift) {
  // delete manual type exports since they'll be covered by next change in this chain
  source
    .find(jscodeshift.ExportNamedDeclaration, {
      exportKind: 'type',
      source: { type: 'StringLiteral' },
    })
    .forEach((typeExport) => typeExport.prune());

  // migrate "export { default as SomeName } from './thing'" to "export * from './thing'"
  source
    .find(jscodeshift.ExportNamedDeclaration, {
      specifiers: [{ type: 'ExportSpecifier', local: { name: 'default' } }],
    })
    .forEach((t) => t.replace(jscodeshift.exportAllDeclaration(t.value.source, null)));
}

const filetypesToIgnore = ['.png', '.jpg', '.jpeg', '.md'];
function migrateDefaultImports(source, jscodeshift) {
  source.find(jscodeshift.ImportDefaultSpecifier).forEach((defaultImport) => {
    const importPath = defaultImport.parent.value.source.value;
    if (importPath.includes('./') && !filetypesToIgnore.some((filetype) => importPath.endsWith(filetype))) {
      defaultImport.replace(jscodeshift.importSpecifier(defaultImport.value.local, null));
    }
  });
}

export default function transformer(file, api) {
  const { jscodeshift } = api;

  const source = jscodeshift.withParser(parser)(file.source);

  migrateDefaultExports(source, jscodeshift, file.path);
  migrateDefaultImports(source, jscodeshift);
  migrateExportDefaultAsStatements(source, jscodeshift);

  return source.toSource();
}