Simplify code to generate line numbers in highlight

src/librustdoc/html/highlight.rs

@@ -343,7 +343,7 @@ struct TokenHandler<'a, 'tcx, F: Write> {
     /// We need to keep the `Class` for each element because it could contain a `Span` which is
     /// used to generate links.
     href_context: Option<HrefContext<'a, 'tcx>>,
-    write_line_number: fn(u32) -> String,
+    write_line_number: fn(u32) -> LineNumber,
     line: u32,
     max_lines: u32,
 }
@@ -355,7 +355,7 @@ impl<F: Write> std::fmt::Debug for TokenHandler<'_, '_, F> {
 }
 
 impl<'a, F: Write> TokenHandler<'a, '_, F> {
-    fn handle_backline(&mut self) -> Option<String> {
+    fn handle_backline(&mut self) -> Option<LineNumber> {
         self.line += 1;
         if self.line < self.max_lines {
             return Some((self.write_line_number)(self.line));
@@ -376,8 +376,7 @@ impl<'a, F: Write> TokenHandler<'a, '_, F> {
         if text == "\n"
             && let Some(backline) = self.handle_backline()
         {
-            self.out.write_str(&text).unwrap();
-            self.out.write_str(&backline).unwrap();
+            write!(self.out, "{text}{backline}").unwrap();
         } else {
             self.push_token_without_backline_check(class, text, true);
         }
@@ -437,20 +436,27 @@ impl<F: Write> Drop for TokenHandler<'_, '_, F> {
     }
 }
 
-fn scraped_line_number(line: u32) -> String {
-    // https://developers.google.com/search/docs/crawling-indexing/robots-meta-tag#data-nosnippet-attr
-    // Do not show "1 2 3 4 5 ..." in web search results.
-    format!("<span data-nosnippet>{line}</span>")
+/// Represents line numbers to be generated as HTML.
+enum LineNumber {
+    /// Used for scraped code examples.
+    Scraped(u32),
+    /// Used for non-scraped code examples, ie source code pages and code examples in documentation.
+    Normal(u32),
+    /// Code examples without line numbers.
+    #[allow(dead_code)]
+    Empty(u32),
 }
 
-fn line_number(line: u32) -> String {
-    // https://developers.google.com/search/docs/crawling-indexing/robots-meta-tag#data-nosnippet-attr
-    // Do not show "1 2 3 4 5 ..." in web search results.
-    format!("<a href=#{line} id={line} data-nosnippet>{line}</a>")
-}
-
-fn empty_line_number(_: u32) -> String {
-    String::new()
+impl Display for LineNumber {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            // https://developers.google.com/search/docs/crawling-indexing/robots-meta-tag#data-nosnippet-attr
+            // Do not show "1 2 3 4 5 ..." in web search results.
+            Self::Scraped(line) => write!(f, "<span data-nosnippet>{line}</span>"),
+            Self::Normal(line) => write!(f, "<a href=#{line} id={line} data-nosnippet>{line}</a>"),
+            Self::Empty(_) => Ok(()),
+        }
+    }
 }
 
 fn get_next_expansion(
@@ -537,12 +543,12 @@ pub(super) fn write_code(
         write_line_number: match line_info {
             Some(line_info) => {
                 if line_info.is_scraped_example {
-                    scraped_line_number
+                    LineNumber::Scraped
                 } else {
-                    line_number
+                    LineNumber::Normal
                 }
             }
-            None => empty_line_number,
+            None => LineNumber::Empty,
         },
         line: 0,
         max_lines: u32::MAX,
@@ -552,8 +558,12 @@ pub(super) fn write_code(
     if let Some(line_info) = line_info {
         token_handler.line = line_info.start_line - 1;
         token_handler.max_lines = line_info.max_lines;
-        if let Some(text) = token_handler.handle_backline() {
-            token_handler.push_token_without_backline_check(None, Cow::Owned(text), false);
+        if let Some(backline) = token_handler.handle_backline() {
+            token_handler.push_token_without_backline_check(
+                None,
+                Cow::Owned(backline.to_string()),
+                false,
+            );
         }
     }