From 8f3753703c9e4e587fcb9790a07aa18b310b8431 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 7 Jun 2019 00:58:32 +0200
Subject: [PATCH] Fix slice const generic length display

---
 src/librustdoc/clean/mod.rs                          |  5 ++++-
 .../rustdoc/const-generics/const-generic-slice.rs    | 12 ++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 src/test/rustdoc/const-generics/const-generic-slice.rs

diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 03d16feb483a9..a717ef20a8444 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -2768,7 +2768,10 @@ impl Clean<Type> for hir::Ty {
                 };
                 let length = match cx.tcx.const_eval(param_env.and(cid)) {
                     Ok(length) => print_const(cx, length),
-                    Err(_) => "_".to_string(),
+                    Err(_) => cx.sess()
+                                .source_map()
+                                .span_to_snippet(cx.tcx.def_span(def_id))
+                                .unwrap_or_else(|_| "_".to_string()),
                 };
                 Array(box ty.clean(cx), length)
             },
diff --git a/src/test/rustdoc/const-generics/const-generic-slice.rs b/src/test/rustdoc/const-generics/const-generic-slice.rs
new file mode 100644
index 0000000000000..60d96770f7eae
--- /dev/null
+++ b/src/test/rustdoc/const-generics/const-generic-slice.rs
@@ -0,0 +1,12 @@
+#![crate_name = "foo"]
+#![feature(const_generics)]
+
+pub trait Array {
+    type Item;
+}
+
+// @has foo/trait.Array.html
+// @has - '//h3[@class="impl"]' 'impl<T, const N: usize> Array for [T; N]'
+impl <T, const N: usize> Array for [T; N] {
+    type Item = T;
+}