Skip formatting for some compiler documentation code

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illustrate how its compilation would be handled, and these examples are
formatted to highlight those aspects in ways that rustfmt wouldn't
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1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index ca57c4f3164..5024c85e2a8 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -356,7 +356,7 @@ impl DefKind {
 /// For example, everything prefixed with `/* Res */` in this example has
 /// an associated `Res`:
 ///
-/// ```
+/// ```ignore (illustrative)
 /// fn str_to_string(s: & /* Res */ str) -> /* Res */ String {
 ///     /* Res */ String::from(/* Res */ s)
 /// }