Enforce dashes in the unstable book file names

Also rename the existing underscore using files to use dashes.

Fixes rust-lang#47394.

Author: est31

src/doc/unstable-book/src/language-features/crate_in_paths.md renamed to src/doc/unstable-book/src/language-features/crate-in-paths.md

@@ -49,7 +49,7 @@ pub fn collect_unstable_feature_names(features: &Features) -> BTreeSet<String> {
     features
         .iter()
         .filter(|&(_, ref f)| f.level == Status::Unstable)
-        .map(|(name, _)| name.to_owned())
+        .map(|(name, _)| name.replace('_', "-"))
         .collect()
 }
 
@@ -60,7 +60,7 @@ pub fn collect_unstable_book_section_file_names(dir: &path::Path) -> BTreeSet<St
         .map(|entry| entry.expect("could not read directory entry"))
         .filter(dir_entry_is_file)
         .map(|entry| entry.file_name().into_string().unwrap())
-        .map(|n| n.trim_right_matches(".md").replace('-', "_"))
+        .map(|n| n.trim_right_matches(".md").to_owned())
         .collect()
 }
 

src/doc/unstable-book/src/language-features/extern_absolute_paths.md renamed to src/doc/unstable-book/src/language-features/extern-absolute-paths.md

@@ -53,9 +53,9 @@ fn set_to_summary_str(set: &BTreeSet<String>, dir: &str
     set
         .iter()
         .map(|ref n| format!("    - [{}]({}/{}.md)",
-                                      n,
+                                      n.replace('-', "_"),
                                       dir,
-                                      n.replace('_', "-")))
+                                      n))
         .fold("".to_owned(), |s, a| s + &a + "\n")
 }
 
@@ -96,14 +96,17 @@ fn generate_unstable_book_files(src :&Path, out: &Path, features :&Features) {
     let unstable_section_file_names = collect_unstable_book_section_file_names(src);
     t!(fs::create_dir_all(&out));
     for feature_name in &unstable_features - &unstable_section_file_names {
-        let file_name = format!("{}.md", feature_name.replace('_', "-"));
+        let feature_name_underscore = feature_name.replace('-', "_");
+        let file_name = format!("{}.md", feature_name);
         let out_file_path = out.join(&file_name);
-        let feature = &features[&feature_name];
+        let feature = &features[&feature_name_underscore];
 
         if has_valid_tracking_issue(&feature) {
-            generate_stub_issue(&out_file_path, &feature_name, feature.tracking_issue.unwrap());
+            generate_stub_issue(&out_file_path,
+                                &feature_name_underscore,
+                                feature.tracking_issue.unwrap());
         } else {
-            generate_stub_no_issue(&out_file_path, &feature_name);
+            generate_stub_no_issue(&out_file_path, &feature_name_underscore);
         }
     }
 }