Add regression test for multi-level import

Author: GuillaumeGomez

Diff for: src/test/rustdoc/multiple-import-levels.rs

@@ -0,0 +1,34 @@
+// The goal of this test is to ensure that the attributes of all imports are taken into
+// account.
+
+#![crate_name = "foo"]
+
+mod a {
+    /// 1
+    pub struct Type;
+}
+
+mod b {
+    /// 2
+    pub use crate::a::Type;
+}
+
+mod c {
+    /// 3
+    pub use crate::b::Type;
+    /// 4
+    pub use crate::b::Type as Woof;
+}
+
+// @has 'foo/struct.Type.html'
+// @has - '//*[@class="rustdoc-toggle top-doc"]/*[@class="docblock"]' 'foo 2 1'
+/// foo
+pub use b::Type;
+// @has 'foo/struct.Whatever.html'
+// @has - '//*[@class="rustdoc-toggle top-doc"]/*[@class="docblock"]' 'whatever 3 2 1'
+/// whatever
+pub use c::Type as Whatever;
+// @has 'foo/struct.Woof.html'
+// @has - '//*[@class="rustdoc-toggle top-doc"]/*[@class="docblock"]' 'a dog 4 2 1'
+/// a dog
+pub use c::Woof;