Multiline string attr display

src/librustdoc/html/render/mod.rs

@@ -3332,6 +3332,16 @@ fn render_attributes(w: &mut Buffer, it: &clean::Item, top: bool) {
                 None
             }
         })
+        // This whole `map` is to correctly print the "cut" strings in attributes arguments like:
+        //
+        // #[x = "string with \
+        //   backline"]
+        .map(|a| {
+            a.split("\\\n").fold(String::new(), |mut acc, a| {
+                acc.push_str(a.trim_start());
+                acc
+            })
+        })
         .join("\n");
 
     if !attrs.is_empty() {

src/test/rustdoc/attributes-backline.rs

@@ -0,0 +1,14 @@
+#![crate_name = "foo"]
+
+// @has 'foo/struct.Fly.html'
+// @has - '//h4[@id="method.drosophilae"]//span[@class="docblock attributes"]' ''
+// @has - '//h4[@id="method.drosophilae"]//span[@class="docblock attributes"]' \
+//    'Just a sentence with a backline in the middle'
+// @!has - '//h4[@id="method.drosophilae"]//span[@class="doblock attributes"]' '\\'
+pub struct Fly;
+
+impl Fly {
+    #[must_use = "Just a sentence with a backline in \
+                  the middle"]
+    pub fn drosophilae(&self) {}
+}