rustdoc: add test for issue-85454

Author: Stupremee

src/test/rustdoc/issue-85454.rs

@@ -0,0 +1,17 @@
+// @has issue_85454/trait.FromResidual.html
+// @has - '//pre[@class="rust trait"]' 'pub trait FromResidual<R = <Self as Try>::Residual> { fn from_residual(residual: R) -> Self; }'
+pub trait FromResidual<R = <Self as Try>::Residual> {
+    fn from_residual(residual: R) -> Self;
+}
+
+pub trait Try: FromResidual {
+    type Output;
+    type Residual;
+    fn from_output(output: Self::Output) -> Self;
+    fn branch(self) -> ControlFlow<Self::Residual, Self::Output>;
+}
+
+pub enum ControlFlow<B, C = ()> {
+    Continue(C),
+    Break(B),
+}