Add more tests for underscore imports

Author: matthewjasper

src/test/ui/underscore-imports/hygiene-2.rs

@@ -0,0 +1,33 @@
+// Make sure that if an underscore imports with different contexts can exist in
+// the same scope.
+
+// check-pass
+
+#![feature(decl_macro)]
+
+mod x {
+    pub use std::ops::Deref as _;
+}
+
+macro n() {
+    pub use crate::x::*;
+}
+
+#[macro_export]
+macro_rules! p {
+    () => { pub use crate::x::*; }
+}
+
+macro m($y:ident) {
+    mod $y {
+        crate::n!(); // Reexport of `Deref` should not be imported in `main`
+        crate::p!(); // Reexport of `Deref` should be imported into `main`
+    }
+}
+
+m!(y);
+
+fn main() {
+    use crate::y::*;
+    (&()).deref();
+}

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

@@ -0,0 +1,31 @@
+// Make sure that if an underscore imports have the same hygiene considerations
+// as other imports.
+
+#![feature(decl_macro)]
+
+mod x {
+    pub use std::ops::Deref as _;
+}
+
+macro m($y:ident) {
+    mod $y {
+        crate::n!();
+    }
+}
+
+macro n() {
+    pub use crate::x::*;
+}
+
+macro p() {
+    use std::ops::DerefMut as _;
+}
+
+m!(y);
+
+fn main() {
+    use crate::y::*;
+    p!();
+    (&()).deref();              //~ ERROR no method named `deref`
+    (&mut ()).deref_mut();      //~ ERROR no method named `deref_mut`
+}

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

@@ -0,0 +1,27 @@
+error[E0599]: no method named `deref` found for type `&()` in the current scope
+  --> $DIR/hygiene.rs:29:11
+   |
+LL |     (&()).deref();
+   |           ^^^^^
+   |
+   = help: items from traits can only be used if the trait is in scope
+help: the following trait is implemented but not in scope, perhaps add a `use` for it:
+   |
+LL | use std::ops::Deref;
+   |
+
+error[E0599]: no method named `deref_mut` found for type `&mut ()` in the current scope
+  --> $DIR/hygiene.rs:30:15
+   |
+LL |     (&mut ()).deref_mut();
+   |               ^^^^^^^^^
+   |
+   = help: items from traits can only be used if the trait is in scope
+help: the following trait is implemented but not in scope, perhaps add a `use` for it:
+   |
+LL | use std::ops::DerefMut;
+   |
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0599`.