resolve: fix bug in visibility of shadowed use declarations

[jseyfried]

This fixes a bug in which the visibility of a use declaration defining a name in one namespace (e.g. the value namespace) is overridden by a later use declaration defining the same name in the other namespace (e.g. the type namespace). For example,

fn f() {}
pub mod bar {}

mod foo {
    use f; // This import should not be visible outside `foo`,
    pub use bar as f; // but it visible outside of `foo` because of this import.
}

fn main() { foo::f(); }

As the example demonstrates, this is a [breaking-change], but it looks unlikely to cause breakage in practice, and any breakage can be fixed by correcting visibility modifiers.

[rust-highfive]

r? @alexcrichton

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[sanxiyn]

cc #30159.

[alexcrichton]

r? @nrc

[jseyfried]

This also fixes #30159.

[nrc]

should this be a labelled continue? It looks like you should continue to the next import_resolution, not to the next namespace

[jseyfried]

No, if the import resolution is not public in one namespace it still could be public in the other namespace. For example, consider

mod foo {}
pub fn f() {}

use foo as bar;
pub use f as bar;

Here, there is a single import_resolution corresponding to bar that is private in the type namespace (i.e. !import_resolution[TypeNS].is_public) but public in the value namespace (i.e. import_resolution[ValueNS].is_public). If we skipped to the next import_resolution after seeing that the type namespace is private, we would not export bar in the value namespace.

[nrc]

LGTM, modulo the two comments

[jseyfried]

@nrc Thanks for the feedback. I addressed both comments.

[nrc]

Sounds good, thanks!

@bors: r+

[bors]

📌 Commit ada87fa has been approved by nrc

[bors]

⌛ Testing commit ada87fa with merge 672a3d9...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt