Add some more tests for underscore imports

src/test/ui/underscore-imports/cycle.rs

@@ -0,0 +1,18 @@
+// Check that cyclic glob imports are allowed with underscore imports
+
+// check-pass
+
+mod x {
+    pub use crate::y::*;
+    pub use std::ops::Deref as _;
+}
+
+mod y {
+    pub use crate::x::*;
+    pub use std::ops::Deref as _;
+}
+
+pub fn main() {
+    use x::*;
+    (&0).deref();
+}

src/test/ui/underscore-imports/shadow.rs

@@ -0,0 +1,23 @@
+// Check that underscore imports don't cause glob imports to be unshadowed
+
+mod a {
+    pub use std::ops::Deref as Shadow;
+}
+
+mod b {
+    pub use crate::a::*;
+    macro_rules! m {
+        ($i:ident) => { pub struct $i; }
+    }
+    m!(Shadow);
+}
+
+mod c {
+    use crate::b::Shadow as _; // Only imports the struct
+
+    fn f(x: &()) {
+        x.deref(); //~ ERROR no method named `deref` found
+    }
+}
+
+fn main() {}

src/test/ui/underscore-imports/shadow.stderr

@@ -0,0 +1,13 @@
+error[E0599]: no method named `deref` found for type `&()` in the current scope
+  --> $DIR/shadow.rs:19:11
+   |
+LL |         x.deref();
+   |           ^^^^^
+   |
+   = help: items from traits can only be used if the trait is in scope
+   = note: the following trait is implemented but not in scope, perhaps add a `use` for it:
+           `use std::ops::Deref;`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.