Rollup merge of rust-lang#47117 - tinaun:no_more_dups, r=frewsxcv

[unstable book] remove duplicate entries

if a unstable feature is a language feature, it shouldn't also have a library feature stub generated

Author: kennytm

src/doc/unstable-book/src/library-features/proc-macro.md

@@ -87,7 +87,9 @@ pub fn check(path: &path::Path, bad: &mut bool) {
     // Library features
 
     let lang_features = collect_lang_features(path);
-    let lib_features = collect_lib_features(path);
+    let lib_features = collect_lib_features(path).into_iter().filter(|&(ref name, _)| {
+        !lang_features.contains_key(name)
+    }).collect();
 
     let unstable_lib_feature_names = collect_unstable_feature_names(&lib_features);
     let unstable_book_lib_features_section_file_names =

src/tools/tidy/src/unstable_book.rs

@@ -129,7 +129,9 @@ fn main() {
     let dest_path = Path::new(&dest_path_str).join("src");
 
     let lang_features = collect_lang_features(src_path);
-    let lib_features = collect_lib_features(src_path);
+    let lib_features = collect_lib_features(src_path).into_iter().filter(|&(ref name, _)| {
+        !lang_features.contains_key(name)
+    }).collect();
 
     let doc_src_path = src_path.join(PATH_STR);