Don't let robots index the print.html (#844)

src/theme/index.hbs

@@ -4,6 +4,10 @@
         <!-- Book generated using mdBook -->
         <meta charset="UTF-8">
         <title>{{ title }}</title>
+        {{#if is_print }}
+        <meta name="robots" content="noindex" />
+        {{/if}}
+
         <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
         <meta name="description" content="{{ description }}">
         <meta name="viewport" content="width=device-width, initial-scale=1">

tests/rendered_output.rs

@@ -415,6 +415,20 @@ fn theme_dir_overrides_work_correctly() {
     dummy_book::assert_contains_strings(built_index, &["This is a modified index.hbs!"]);
 }
 
+
+#[test]
+fn no_index_for_print_html() {
+    let temp = DummyBook::new().build().unwrap();
+    let md = MDBook::load(temp.path()).unwrap();
+    md.build().unwrap();
+
+    let print_html = temp.path().join("book/print.html");
+    assert_contains_strings(print_html, &[r##"noindex"##]);
+
+    let index_html = temp.path().join("book/index.html");
+    assert_doesnt_contain_strings(index_html, &[r##"noindex"##]);
+}
+
 #[cfg(feature = "search")]
 mod search {
     extern crate serde_json;