Don't resolve shadowed arguments variables from functions

[The-x-Theorist]

Q	A
Fixed Issues?	Fixes #13990
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Function's implicit argument binding now won't fail because the arguments identifier in function will be renamed differently than the arguments identifier in any another scope.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/50332/

[nicolo-ribaudo]

The fix should be inside the renamer. You can edit this code:

babel/packages/babel-traverse/src/scope/lib/renamer.ts

Lines 21 to 26 in 3908049

	if (
	!path.scope.bindingIdentifierEquals(
	state.oldName,
	state.binding.identifier,
	)
	) {

to also skip if state.oldName === "arguments" && path.isFunction() && !path.isArrowFunctionExpression().

[nicolo-ribaudo]

Or even better, if it works, in getBinding (so that bindingIdentifierEquals then returns false):

babel/packages/babel-traverse/src/scope/index.ts

Lines 1116 to 1144 in 3908049

	getBinding(name: string): Binding | undefined {
	let scope: Scope = this;
	let previousPath;
	do {
	const binding = scope.getOwnBinding(name);
	if (binding) {
	// Check if a pattern is a part of parameter expressions.
	// Note: for performance reason we skip checking previousPath.parentPath.isFunction()
	// because `scope.path` is validated as scope in packages/babel-types/src/validators/isScope.js
	// That is, if a scope path is pattern, its parent must be Function/CatchClause
	// Spec 9.2.10.28: The closure created by this expression should not have visibility of
	// declarations in the function body. If the binding is not a `param`-kind (as function parameters)
	// or `local`-kind (as id in function expression),
	// then it must be defined inside the function body, thus it should be skipped
	if (
	previousPath?.isPattern() &&
	binding.kind !== "param" &&
	binding.kind !== "local"
	) {
	// do nothing
	} else {
	return binding;
	}
	}
	previousPath = scope.path;
	} while ((scope = scope.parent));
	}

If !binding && name === "arguments" && scope.path.isFunction() && !scope.path.isArrowFunctionExpression(), we can break the loop and return undefined. This is because in this code:

var arguments = [];
function f() {
  return arguments;
}

the return arguments does not refer to var arguments.

[The-x-Theorist]

@nicolo-ribaudo Okay, I got I will make the changes just as you described in the next commit.

[nicolo-ribaudo]

Thanks!

[nicolo-ribaudo]

The Babel 8 tests are failing because you didn't specify any target here. Could you move this test in the arrow functions plugin, and enable the plugin instead of the preset?
Also, please specify "sourceType": "script" since this is specific to loose mode.

[The-x-Theorist]

Okay, I can do that.

[The-x-Theorist]

I changed the same as you said.

[lightmare]

Note for self and others: this is correct, the test was previously broken — fn should not see the outer arguments, because it was not an arrow function in input.js