add "text" sections for things that seem likely to be a problem

src/librustc/infer/canonical.rs

@@ -457,7 +457,9 @@ fn unify_canonical_vars(
     /// *also* replace all free regions whatsoever. So for example a
     /// query like `T: Trait<'static>` would be canonicalized to
     ///
-    ///     T: Trait<'?0>
+    /// ```text
+    /// T: Trait<'?0>
+    /// ```
     ///
     /// with a mapping M that maps `'?0` to `'static`.
     ///
@@ -486,7 +488,9 @@ pub fn canonicalize_query<V>(&self, value: &V) -> (V::Canonicalized, CanonicalVa
     /// there was an input query `T: Trait<'static>`, it would have
     /// been canonicalized to
     ///
-    ///     T: Trait<'?0>
+    /// ```text
+    /// T: Trait<'?0>
+    /// ```
     ///
     /// with a mapping M that maps `'?0` to `'static`. But if we found that there
     /// exists only one possible impl of `Trait`, and it looks like