[Bug]: Parser throws when var declaration and function declaration in class static block

[overlookmotel]

💻

• Would you like to work on a fix?

How are you using Babel?

Programmatic API (babel.transform, babel.parse)

Input code

class X {
  static {
    var x;
    function x() {}
  }
}

REPL

Configuration file name

No response

Configuration

n/a

Current and expected behavior

I believe that the above code is legal. It happily runs in NodeJS.

Babel's parser throws an error Identifier 'x' has already been declared.

This only applies within a class static block. The following parses correctly (when sourceType: 'script'):

var x; function x() {}
class X {
  foo() { var x; function x() {} }
  static foo() { var x; function x() {} }
}
function f() { var x; function x() {} }
() => { var x; function x() {} };
function f2() { 'use strict'; var x; function x() {} }
() => { 'use strict'; var x; function x() {} };

REPL

Environment

System:
  OS: macOS 10.15.7
Binaries:
  Node: 16.14.0 - ~/.nvm/versions/node/v16.14.0/bin/node
  npm: 8.3.1 - ~/.nvm/versions/node/v16.14.0/bin/npm
npmPackages:
  @babel/core: ^7.17.2 => 7.17.2
  @babel/generator: ^7.17.0 => 7.17.0
  @babel/helper-module-transforms: ^7.16.7 => 7.16.7
  @babel/helper-plugin-utils: ^7.16.7 => 7.16.7
  @babel/parser: ^7.17.0 => 7.17.0
  @babel/plugin-transform-arrow-functions: ^7.16.7 => 7.16.7
  @babel/plugin-transform-modules-commonjs: ^7.16.8 => 7.16.8
  @babel/plugin-transform-react-jsx: ^7.16.7 => 7.16.7
  @babel/plugin-transform-strict-mode: ^7.16.7 => 7.16.7
  @babel/traverse: ^7.17.0 => 7.17.0
  @babel/types: ^7.17.0 => 7.17.0
  babel-plugin-dynamic-import-node: ^2.3.3 => 2.3.3
  eslint: ^7.32.0 => 7.32.0
  jest: ^27.5.1 => 27.5.1

Possible solution

No response

Additional context

Happy to work on a PR. But could someone please point in right direction? I'm not at all familiar with the parser.

[babel-bot]

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[JLHwung]

The error is thrown from

babel/packages/babel-parser/src/util/scope.js

Line 152 in 76dd491

this.raise(Errors.VarRedeclaration, { at: loc }, name);

When Babel is parsing a static block, it will push a SCOPE_STATIC_BLOCK

babel/packages/babel-parser/src/parser/statement.js

Line 1746 in 76dd491

this.scope.enter(SCOPE_CLASS | SCOPE_STATIC_BLOCK | SCOPE_SUPER);

I think we should handle that in

babel/packages/babel-parser/src/util/scope.js

Line 103 in 76dd491

treatFunctionsAsVarInScope(scope: IScope): boolean {

Alternatively, we can enable SCOPE_FUNCTION flag instead(I didn't try). Intuitively the static block is a function body so SCOPE_FUNCTION may be applied, too.

[nicolo-ribaudo]

@overlookmotel I'm assigning this to you since you selected "Would you like to work on a fix?". If you are not interested anymore just leave a comment!

[Yokubjon-J]

I would be happy to take on this issue @nicolo-ribaudo .

[overlookmotel]

@Yokubjon-J I'd be very happy if you did! I was going to, but I'm unfamiliar with the parser code base, so will probably take me a while.

[Yokubjon-J]

please assign me, @nicolo-ribaudo. i have started working on the issue.

[Yokubjon-J]

For some unknown reason, I am getting the error false != [object Object] in .ast after running test inside fixtures subdirectory (one in \babel-parser\test\fixtures\es2015\class\static-block\input.js another in \babel-parser\test\fixtures\static\class-static-method\input.js, shown in the picture below, their contents are not the same).
I think the test file directories are organized correctly, I would like to know your suggestions.

[nicolo-ribaudo]

That might be a bug in our test runner; what does it say if you set the OVERWRITE=true environment variable when calling running out tests?

[Yokubjon-J]

Thanks, it worked! I am back to the issue.

[Yokubjon-J]

@nicolo-ribaudo when i write tests inside already created folders, they execute normally.
But after creating my own new folder inside fixtures, (\babel-parser\test\fixtures\static\class-static-block), even after setting OVERWRITE=true, i get the error Error: ENOENT: no such file or directory, open 'C:\Users\User\Desktop\Projects\babel\packages\babel-parser\test\fixtures\static\class-static-block\input.js\output.json'. Would you like to suggest something about it?

[Yokubjon-J]

i am trying to commit changes but i am getting the error ESLint couldn't find the plugin "@babel/eslint-plugin-development. i tried installing it but it also throws an error npm ERR! Cannot read properties of null (reading 'package'). any suggestions?

[JLHwung]

@Yokubjon-J Please run yarn to install dependencies. If you are developing on Windows, you can also run make bootstrap in the embedded Linux, mingw64 may not be well supported since we don't run CI on mingw64 environment.

[Yokubjon-J]

pull request 14336

[overlookmotel]

@Yokubjon-J Just want to say thanks loads for fixing this.

[Yokubjon-J]

@overlookmotel thank you also for letting me have this bug (to fix)!