add tests and slight formatting

src/test/ui/marker_trait_attr/overlap-marker-trait-with-static-lifetime.rs

@@ -0,0 +1,10 @@
+// check-pass
+#![feature(marker_trait_attr)]
+
+#[marker]
+trait Marker {}
+
+impl Marker for &'static () {}
+impl Marker for &'static () {}
+
+fn main() {}

src/test/ui/marker_trait_attr/overlap-marker-trait-with-underscore-lifetime.rs

@@ -0,0 +1,9 @@
+#![feature(marker_trait_attr)]
+
+#[marker]
+trait Marker {}
+
+impl Marker for &'_ () {} //~ ERROR type annotations needed
+impl Marker for &'_ () {} //~ ERROR type annotations needed
+
+fn main() {}

src/test/ui/marker_trait_attr/overlap-marker-trait-with-underscore-lifetime.stderr

@@ -0,0 +1,31 @@
+error[E0283]: type annotations needed: cannot satisfy `&(): Marker`
+  --> $DIR/overlap-marker-trait-with-underscore-lifetime.rs:6:6
+   |
+LL | impl Marker for &'_ () {}
+   |      ^^^^^^
+   |
+note: multiple `impl`s satisfying `&(): Marker` found
+  --> $DIR/overlap-marker-trait-with-underscore-lifetime.rs:6:1
+   |
+LL | impl Marker for &'_ () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^
+LL | impl Marker for &'_ () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0283]: type annotations needed: cannot satisfy `&(): Marker`
+  --> $DIR/overlap-marker-trait-with-underscore-lifetime.rs:7:6
+   |
+LL | impl Marker for &'_ () {}
+   |      ^^^^^^
+   |
+note: multiple `impl`s satisfying `&(): Marker` found
+  --> $DIR/overlap-marker-trait-with-underscore-lifetime.rs:6:1
+   |
+LL | impl Marker for &'_ () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^
+LL | impl Marker for &'_ () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0283`.

src/test/ui/marker_trait_attr/overlap-marker-trait.rs

@@ -7,7 +7,8 @@
 
 use std::fmt::{Debug, Display};
 
-#[marker] trait Marker {}
+#[marker]
+trait Marker {}
 
 impl<T: Debug> Marker for T {}
 impl<T: Display> Marker for T {}

src/test/ui/marker_trait_attr/overlap-marker-trait.stderr

@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `NotDebugOrDisplay: Marker` is not satisfied
-  --> $DIR/overlap-marker-trait.rs:27:17
+  --> $DIR/overlap-marker-trait.rs:28:17
    |
 LL |     is_marker::<NotDebugOrDisplay>();
    |                 ^^^^^^^^^^^^^^^^^ the trait `Marker` is not implemented for `NotDebugOrDisplay`
    |
 note: required by a bound in `is_marker`
-  --> $DIR/overlap-marker-trait.rs:15:17
+  --> $DIR/overlap-marker-trait.rs:16:17
    |
 LL | fn is_marker<T: Marker>() { }
    |                 ^^^^^^ required by this bound in `is_marker`

src/test/ui/marker_trait_attr/overlap-permitted-for-annotated-marker-traits.rs

@@ -7,7 +7,8 @@
 
 use std::fmt::{Debug, Display};
 
-#[marker] trait MyMarker {}
+#[marker]
+trait MyMarker {}
 
 impl<T: Debug> MyMarker for T {}
 impl<T: Display> MyMarker for T {}