fix: accept duplicated import/variable in different module

[colinaaa]

Q	A
Fixed Issues?	Fixes #13510
Patch: Bug Fix?	👍
Major: Breaking Change?	Not sure
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

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

Lines 201 to 212 in fce35af

	Declaration(path) {
	// delegate block scope handling to the `BlockScoped` method
	if (path.isBlockScoped()) return;
	// this will be hit again once we traverse into it after this iteration
	if (path.isExportDeclaration()) return;
	// we've ran into a declaration!
	const parent =
	path.scope.getFunctionParent() || path.scope.getProgramParent();
	parent.registerDeclaration(path);
	},

I make all ImportDeclaration isBlockScoped, so that it will getBlockParent instead of getProgramParent (which leads to conflicts).

I'm not sure this is the best way to do so, but since Declaration and BlockScoped visitor of collectorVisitor are doing similar things, it sounds like pretty good to me.

According to the test, this change did not bring any breaking change. However, I not so familiar with babel codebase. So there are possibilities that this PR is breaking something.

Let me know if this approach is not correct / breaking, I will try to find another way out.

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[fedeci]

Actually it is not block scoped as ImportDeclarations may only appear in the top level or inside a module/namespace (for TS). Adding it here may be a breaking change for someone using the validator.
Furthermore excluding ImportDeclarations from

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

Lines 201 to 212 in fce35af

	Declaration(path) {
	// delegate block scope handling to the `BlockScoped` method
	if (path.isBlockScoped()) return;
	// this will be hit again once we traverse into it after this iteration
	if (path.isExportDeclaration()) return;
	// we've ran into a declaration!
	const parent =
	path.scope.getFunctionParent() || path.scope.getProgramParent();
	parent.registerDeclaration(path);
	},

results in excluding those nodes from the traversal and not running registerDeclaration on them.

[colinaaa]

I don't think excluding ImportDeclarations is well enough, since it will also cause breaking changes.

The main problem here is that the scope of declared module should be isolated with other modules' scopes and the program's scope. But unfortunately it's not now.

So maybe we could change the implementation of getProgramParent to make it returns not only on Program, but also ModuleDeclaration. This will make scopes of modules isolated with each other and the program.

[fedeci]

Yep, excluding ImportDeclaration is definitely not the right way here.
You will be happy to know that there is already a method called getBlockParent that gets the upper block. However I would suggest you to give a look at how the BlockScoped visitor is handling block scoped declarations, because we may have to replicate a similar behavior for ImportDeclaration.

[JLHwung]

make it returns not only on Program, but also ModuleDeclaration.

I don't think we can mark ModuleDeclaration as program because variables within module declaration can reference bindings defined in program:

type T = number;
declare module 'test' {
  declare var a: T;
}

Since ambient declarations are always top level. We can check if node.parent is ModuleDeclaration and then register declarations there, otherwise we fallback to

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

Lines 209 to 210 in fce35af

	const parent =
	path.scope.getFunctionParent() || path.scope.getProgramParent();

[colinaaa]

I took a different approach.

Take all ImportDeclaration into a separated visitor, and use getBlockParent to find parent scope.

I think it is more conducive to maintenance。

[nicolo-ribaudo]

Thanks!