add tests for doc coverage

src/test/rustdoc-ui/coverage/traits.rs

@@ -0,0 +1,37 @@
+// compile-flags:-Z unstable-options --show-coverage
+// compile-pass
+
+#![feature(trait_alias)]
+
+/// look at this trait right here
+pub trait ThisTrait {
+    /// that's a trait all right
+    fn right_here(&self);
+
+    /// even the provided functions show up as trait methods
+    fn aww_yeah(&self) {}
+
+    /// gotta check those associated types, they're slippery
+    type SomeType;
+}
+
+/// so what happens if we take some struct...
+pub struct SomeStruct;
+
+/// ...and slap this trait on it?
+impl ThisTrait for SomeStruct {
+    /// what we get is a perfect combo!
+    fn right_here(&self) {}
+
+    type SomeType = String;
+}
+
+/// but what about those aliases? i hear they're pretty exotic
+pub trait MyAlias = ThisTrait + Send + Sync;
+
+// FIXME(58624): once rustdoc can process existential types, we need to make sure they're counted
+// /// woah, getting all existential in here
+// pub existential type ThisExists: ThisTrait;
+//
+// /// why don't we get a little more concrete
+// pub fn defines() -> ThisExists { SomeStruct {} }