Fix mod from inline mod in non-mod-rs.

[ehuss]

This works under the assumption that filesystem paths should match mod paths.

When a mod is loaded from within an inline mod, it was using the wrong path when
inside a non-mod-rs file. It was not including the path components from the
non-mod-rs file.

This change also includes:

• Added a test to the run-pass test.
• Added a test to verify the error message when missing.
• Remove unused non_modrs_mods for feature gate diagnostics.
• Fixes the run-pass test, it was accidentally removed during stabilization.
• Remove the vestiges of the feature gate tests in test/ui.
• Enable the diagnostic test on windows, there didn't seem to be a reason to
  disable it.

Fixes #55094

[rust-highfive]

r? @pnkfelix

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[ehuss]

There is a second commit that fixes it for #[path] attributes as well. However, I think it will break rustfmt. I vaguely recall that tools can't be broken at certain times, so I'm not sure what to do about that.

[rust-highfive]

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

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[00:55:52] 
[00:55:52] ------------------------------------------
[00:55:52] stderr:
[00:55:52] ------------------------------------------
[00:55:52] {"message":"couldn't read \"/checkout/src/test/run-pass/modules/mod_dir_simple/load_another_mod/test.rs\": No such file or directory (os error 2)","code":null,"level":"error","spans":[{"file_name":"/checkout/src/test/run-pass/modules/mod_dir_simple/load_another_mod.rs","byte_start":507,"byte_end":511,"line_start":13,"line_end":13,"column_start":9,"column_end":13,"is_primary":true,"text":[{"text":"pub mod test;","highlight_start":9,"highlight_end":13}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error: couldn't read \"/checkout/src/test/run-pass/modules/mod_dir_simple/load_another_mod/test.rs\": No such file or directory (os error 2)\n  --> /checkout/src/test/run-pass/modules/mod_dir_simple/load_another_mod.rs:13:9\n   |\nLL | pub mod test;\n   |         ^^^^\n\n"}
[00:55:52] {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
[00:55:52] ------------------------------------------
[00:55:52] 
[00:55:52] thread '[run-pass] run-pass/modules/mod_dir_recursive.rs' panicked at 'explicit panic', tools/compiletest/src/runtest.rs:3277:9
[00:55:52] note: Run with `RUST_BACKTRACE=1` for a backtrace.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[ehuss]

Well bummer. Apparently non-mod-rs behavior was always possible with #[path] attributes, but the path is never included the path of the root module where the #[path] appears. That really throws a wrench into this fix. 😞

So, stable rust supported this:

main.rs:
    mod foo;
    fn main() {
        foo::inline::inline2::bar::f();
    }

foo.rs:
    pub mod inline {
        pub mod inline2 {
            #[path="baz.rs"]
            pub mod bar;
        }
    }

inline/inline2/baz.rs:
    pub fn f () {}

Notice the distinct lack of foo in the baz.rs path and no mod.rs files.

I can't think of a way, yet, to continue to support this while fixing the original issue. It's getting late here, so I'll need to pick it up tomorrow.

[ehuss]

I've been trying to think of a solution to the above, but I'm running out of ideas. Some (bad) ideas:

• Replace Directory::path with a stack that can filter out non-mod-rs ids when used with #[path] attributes in inline mods. This sounds awful.
• Just make a breaking change to #[path] in inline modules in non-mod-rs files. There were no tests for it, and I don't see anyone doing that on crates.io.

And just to be clear, I would propose leaving original #[path] behavior for all other cases (does not include the id of a non-mod-rs module). This may be confusing, but I don't think it can be changed without breakage. I think the simplicity of module path = directory path is beneficial for the 99% of users who never use #[path].

Let me know if anyone has any ideas.

[pnkfelix]

sorry for not getting around to revewing this yet

[pnkfelix]

@ehuss I see that you've started comparing this PR to PR #55192. Are you okay with me closing this and letting the future activity be focused on #55192?

[ehuss]

Yea, that's fine. However, some of the fixes here should not get lost.