Rollup merge of #47726 - pietroalbini:fix-nested-empty-groups-span, r=petrochenkov

Fix spans in unused import lint for nested groups

This fixes an inconsistency for empty nested groups, and adds a test for all the possible cases of the lint.

```
warning: unused imports: `*`, `Foo`, `baz::{}`, `foobar::*`
  --> test.rs:16:11
   |
16 | use foo::{Foo, bar::{baz::{}, foobar::*}, *};
   |           ^^^        ^^^^^^^  ^^^^^^^^^   ^
   |
   = note: #[warn(unused_imports)] on by default

warning: unused import: `*`
  --> test.rs:17:24
   |
17 | use foo::bar::baz::{*, *};
   |                        ^

warning: unused import: `use foo::{};`
  --> test.rs:18:1
   |
18 | use foo::{};
   | ^^^^^^^^^^^^
```

cc #44494

3 files changed, 42 insertions, 17 deletions

diff --git a/src/test/ui/owl-import-generates-unused-import-lint.stderr b/src/test/ui/owl-import-generates-unused-import-lint.stderr
deleted file mode 100644
index 79089b2a93c..00000000000
--- a/src/test/ui/owl-import-generates-unused-import-lint.stderr
+++ /dev/null
@@ -1,14 +0,0 @@
-error: unused import: `*`
-  --> $DIR/owl-import-generates-unused-import-lint.rs:18:14
-   |
-18 | use foo::{*, *}; //~ ERROR unused import: `*`
-   |              ^
-   |
-note: lint level defined here
-  --> $DIR/owl-import-generates-unused-import-lint.rs:12:9
-   |
-12 | #![deny(unused_imports)]
-   |         ^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-
diff --git a/src/test/ui/owl-import-generates-unused-import-lint.rs b/src/test/ui/use-nested-groups-unused-imports.rs
index dc30c318352..ddbf54fdd48 100644
--- a/src/test/ui/owl-import-generates-unused-import-lint.rs
+++ b/src/test/ui/use-nested-groups-unused-imports.rs
@@ -1,4 +1,4 @@
-// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -9,13 +9,26 @@
 // except according to those terms.
 
 #![feature(use_nested_groups)]
+#![allow(dead_code)]
 #![deny(unused_imports)]
 
 mod foo {
-    pub enum Bar {}
+    pub mod bar {
+        pub mod baz {
+            pub struct Bar();
+        }
+        pub mod foobar {}
+    }
+
+    pub struct Foo();
 }
 
-use foo::{*, *}; //~ ERROR unused import: `*`
+use foo::{Foo, bar::{baz::{}, foobar::*}, *};
+    //~^ ERROR unused imports: `*`, `Foo`, `baz::{}`, `foobar::*`
+use foo::bar::baz::{*, *};
+    //~^ ERROR unused import: `*`
+use foo::{};
+    //~^ ERROR unused import: `use foo::{};`
 
 fn main() {
     let _: Bar;
diff --git a/src/test/ui/use-nested-groups-unused-imports.stderr b/src/test/ui/use-nested-groups-unused-imports.stderr
new file mode 100644
index 00000000000..0686310dbf5
--- /dev/null
+++ b/src/test/ui/use-nested-groups-unused-imports.stderr
@@ -0,0 +1,26 @@
+error: unused imports: `*`, `Foo`, `baz::{}`, `foobar::*`
+  --> $DIR/use-nested-groups-unused-imports.rs:26:11
+   |
+26 | use foo::{Foo, bar::{baz::{}, foobar::*}, *};
+   |           ^^^        ^^^^^^^  ^^^^^^^^^   ^
+   |
+note: lint level defined here
+  --> $DIR/use-nested-groups-unused-imports.rs:13:9
+   |
+13 | #![deny(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+error: unused import: `*`
+  --> $DIR/use-nested-groups-unused-imports.rs:28:24
+   |
+28 | use foo::bar::baz::{*, *};
+   |                        ^
+
+error: unused import: `use foo::{};`
+  --> $DIR/use-nested-groups-unused-imports.rs:30:1
+   |
+30 | use foo::{};
+   | ^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+