Rollup merge of #47298 - cramertj:path-as-modrs, r=nikomatsakis

Treat #[path] files as mod.rs files

Fixes https://github.com/rust-lang/rust/issues/46936, cc @briansmith, @SergioBenitez, @nikomatsakis.

This (insta-stable) change treats files included via `#[path = "bla.rs"] mod foo;` as though they were `mod.rs` files. Namely, it allows them to include `mod` statements and looks for the child modules in sibling directories, rather than in relative `modname/childmodule.rs` files as happens for non-`mod.rs` files.

This change makes the `non_modrs_mods` feature backwards compatible with the existing usage in https://github.com/briansmith/ring, several versions of which are currently broken in beta. If we decide to merge, this change should be backported to beta.

cc https://github.com/rust-lang/rust/issues/37872

r? @jseyfried

src/test/compile-fail/directory_ownership/backcompat-warnings.rs

@@ -1,16 +0,0 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-// error-pattern: mod statements in non-mod.rs files are unstable
-
-#[path="mod_file_not_owning_aux3.rs"]
-mod foo;
-
-fn main() {}

src/test/ui/non_modrs_mods/non_modrs_mods.stderr

@@ -34,14 +34,5 @@ error: mod statements in non-mod.rs files are unstable (see issue #44660)
    = help: add #![feature(non_modrs_mods)] to the crate attributes to enable
    = help: on stable builds, rename this file to inner_foors_mod/mod.rs
 
-error: mod statements in non-mod.rs files are unstable (see issue #44660)
-  --> $DIR/some_crazy_attr_mod_dir/arbitrary_name.rs:11:9
-   |
-11 | pub mod inner_modrs_mod;
-   |         ^^^^^^^^^^^^^^^
-   |
-   = help: add #![feature(non_modrs_mods)] to the crate attributes to enable
-   = help: on stable builds, rename this file to attr_mod/mod.rs
-
-error: aborting due to 5 previous errors
+error: aborting due to 4 previous errors