'__sfc_main' has already been declared.

[jaxonly]

a minimal reproduction

https://github.com/JaxXu/sugartake2try

intro

 ERROR  Failed to compile with 1 error                                                                                                                                                          7:28:01 PM

 error  in ./src/js/App.vue?vue&type=script&lang=js&

Syntax Error: Identifier '__sfc_main' has already been declared. (19:6)

  17 |   Old
  18 | }, __sfc_main.components);
> 19 | const __sfc_main = __sfc_main;
     |       ^
  20 | export default __sfc_main;
  21 |

This bug recurs when placing the Vue2ScriptSetupPlugin plugin in front of the VueLoaderPlugin, Maybe some additional documentation is needed

But the above case is not a percentage recurrence, you remove the /* unlock comment */ from App.vue and the error will not be reported. Is this also a bug? As far as I can see, when transformScriptSetup is processed, the problem is that the ParsedSFC object does not contain scriptSetup but script

error

=============== ↓ ↓ ↓ ↓ ↓ ↓ ↓ transformScriptSetup.sfc ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ==================
{
  id: '/Users/xuyihao/Documents/GitHub.nosync/webpack5/packages/dev/src/js/App.vue?vue&type=script&lang=js&',
  template: {
    components: Set(2) { 'New', 'Old' },
    identifiers: Set(2) { 'readersNumber', 'add' }
  },
  scriptSetup: {
    start: 0,
    end: 0,
    contentStart: 0,
    contentEnd: 0,
    content: '',
    attrs: {},
    found: false,
    ast: Node {
      type: 'Program',
      start: 0,
      end: 0,
      loc: [SourceLocation],
      sourceType: 'module',
      interpreter: null,
      body: [],
      directives: []
    }
  },
  script: {
    start: 273,
    end: 644,
    contentStart: 282,
    contentEnd: 635,
    content: '\n' +
      "import New from './components/new';\n" +
      "import Old from './components/old'; // let readersNumber = $ref(0);\n" +
      '//\n' +
      '// const add = () => {\n' +
      '//     readersNumber += 1;\n' +
      '// }\n' +
      '\n' +
      'const __sfc_main = {};\n' +
      '\n' +
      '__sfc_main.setup = (__props, __ctx) => {\n' +
      '  return {};\n' +
      '};\n' +
      '\n' +
      '__sfc_main.components = Object.assign({\n' +
      '  New,\n' +
      '  Old\n' +
      '}, __sfc_main.components);\n' +
      'export default __sfc_main;\n',
    attrs: {},
    found: true,
    ast: Node {
      type: 'Program',
      start: 0,
      end: 353,
      loc: [SourceLocation],
      sourceType: 'module',
      interpreter: null,
      body: [Array],
      directives: []
    }
  },
  parserOptions: { sourceType: 'module', plugins: [] },
  extraDeclarations: []
}

=============== ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ generate(ast).code ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ==================

import New from './components/new';
import Old from './components/old'; // let readersNumber = $ref(0);
//
// const add = () => {
//     readersNumber += 1;
// }

const __sfc_main = {};

__sfc_main.setup = (__props, __ctx) => {
  return {};
};

__sfc_main.components = Object.assign({
  New,
  Old
}, __sfc_main.components);
const __sfc_main = __sfc_main;
export default __sfc_main;

normal

=============== ↓ ↓ ↓ ↓ ↓ ↓ ↓ transformScriptSetup.sfc ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ==================
{
  id: '/Users/xuyihao/Documents/GitHub.nosync/webpack5/packages/dev/src/js/App.vue?vue&type=script&lang=js&',
  template: {
    components: Set(2) { 'New', 'Old' },
    identifiers: Set(2) { 'readersNumber', 'add' }
  },
  scriptSetup: {
    start: 273,
    end: 460,
    contentStart: 287,
    contentEnd: 451,
    content: '\n' +
      "import New from './components/new';\n" +
      "import Old from './components/old';\n" +
      '\n' +
      '// let readersNumber = $ref(0);\n' +
      '//\n' +
      '// const add = () => {\n' +
      '//     readersNumber += 1;\n' +
      '// }\n',
    attrs: { setup: '' },
    found: true,
    ast: Node {
      type: 'Program',
      start: 0,
      end: 164,
      loc: [SourceLocation],
      sourceType: 'module',
      interpreter: null,
      body: [Array],
      directives: []
    }
  },
  script: {
    start: 0,
    end: 0,
    contentStart: 0,
    contentEnd: 0,
    content: '',
    attrs: {},
    found: false,
    ast: Node {
      type: 'Program',
      start: 0,
      end: 0,
      loc: [SourceLocation],
      sourceType: 'module',
      interpreter: null,
      body: [],
      directives: []
    }
  },
  parserOptions: { sourceType: 'module', plugins: [] },
  extraDeclarations: []
}

=============== ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ generate(ast).code ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ==================

import New from './components/new';
import Old from './components/old'; // let readersNumber = $ref(0);
//
// const add = () => {
//     readersNumber += 1;
// }

const __sfc_main = {};

__sfc_main.setup = (__props, __ctx) => {
  return {};
};

__sfc_main.components = Object.assign({
  New,
  Old
}, __sfc_main.components);
export default __sfc_main;
============