Fix failing examples

compiler/rustc_lint/src/let_underscore.rs

@@ -11,7 +11,7 @@ declare_lint! {
     /// scope.
     ///
     /// ### Example
-    /// ```
+    /// ```rust
     /// struct SomeStruct;
     /// impl Drop for SomeStruct {
     ///     fn drop(&mut self) {

compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs

@@ -26,19 +26,23 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```
+    /// ```rust
+    /// trait Duh {}
+    ///
+    /// impl Duh for i32 {}
+    ///
     /// trait Trait {
-    ///     type Assoc: Send;
+    ///     type Assoc: Duh;
     /// }
     ///
     /// struct Struct;
     ///
-    /// impl Trait for Struct {
+    /// impl<F: Duh> Trait for F {
-    ///     type Assoc = i32;
+    ///     type Assoc = F;
     /// }
     ///
     /// fn test() -> impl Trait<Assoc = impl Sized> {
-    ///     Struct
+    ///     42
     /// }
     /// ```
     ///

compiler/rustc_lint_defs/src/builtin.rs

@@ -605,7 +605,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```
+    /// ```rust
     /// #[warn(unused_tuple_struct_fields)]
     /// struct S(i32, i32, i32);
     /// let s = S(1, 2, 3);
@@ -1154,7 +1154,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```compile_fail
+    /// ```rust,compile_fail
     /// #[repr(packed)]
     /// pub struct Foo {
     ///     field1: u64,
@@ -2615,7 +2615,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```compile_fail
+    /// ```rust,compile_fail
     /// # #![allow(unused)]
     /// enum E {
     ///     A,
@@ -3986,7 +3986,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```
+    /// ```rust
     /// #![allow(test_unstable_lint)]
     /// ```
     ///