Fewer temporary strings

src/librustdoc/formats/item_type.rs

@@ -158,6 +158,6 @@ impl ItemType {
 
 impl fmt::Display for ItemType {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.as_str())
+        f.write_str(self.as_str())
     }
 }

src/librustdoc/html/highlight.rs

@@ -7,24 +7,26 @@
 
 use crate::html::escape::Escape;
 
-use std::fmt::{Display, Write};
+use std::fmt::Display;
 use std::iter::Peekable;
 
 use rustc_lexer::{LiteralKind, TokenKind};
 use rustc_span::edition::Edition;
 use rustc_span::symbol::Symbol;
 use rustc_span::with_default_session_globals;
 
+use super::format::Buffer;
+
 /// Highlights `src`, returning the HTML output.
 crate fn render_with_highlighting(
     src: &str,
+    out: &mut Buffer,
     class: Option<&str>,
     playground_button: Option<&str>,
     tooltip: Option<(Option<Edition>, &str)>,
     edition: Edition,
-) -> String {
+) {
     debug!("highlighting: ================\n{}\n==============", src);
-    let mut out = String::with_capacity(src.len());
     if let Some((edition_info, class)) = tooltip {
         write!(
             out,
@@ -35,23 +37,19 @@ crate fn render_with_highlighting(
             } else {
                 String::new()
             },
-        )
-        .unwrap();
+        );
     }
 
-    write_header(&mut out, class);
-    write_code(&mut out, &src, edition);
-    write_footer(&mut out, playground_button);
-
-    out
+    write_header(out, class);
+    write_code(out, &src, edition);
+    write_footer(out, playground_button);
 }
 
-fn write_header(out: &mut String, class: Option<&str>) {
-    write!(out, "<div class=\"example-wrap\"><pre class=\"rust {}\">\n", class.unwrap_or_default())
-        .unwrap()
+fn write_header(out: &mut Buffer, class: Option<&str>) {
+    write!(out, "<div class=\"example-wrap\"><pre class=\"rust {}\">\n", class.unwrap_or_default());
 }
 
-fn write_code(out: &mut String, src: &str, edition: Edition) {
+fn write_code(out: &mut Buffer, src: &str, edition: Edition) {
     // This replace allows to fix how the code source with DOS backline characters is displayed.
     let src = src.replace("\r\n", "\n");
     Classifier::new(&src, edition).highlight(&mut |highlight| {
@@ -63,8 +61,8 @@ fn write_code(out: &mut String, src: &str, edition: Edition) {
     });
 }
 
-fn write_footer(out: &mut String, playground_button: Option<&str>) {
-    write!(out, "</pre>{}</div>\n", playground_button.unwrap_or_default()).unwrap()
+fn write_footer(out: &mut Buffer, playground_button: Option<&str>) {
+    write!(out, "</pre>{}</div>\n", playground_button.unwrap_or_default());
 }
 
 /// How a span of text is classified. Mostly corresponds to token kinds.
@@ -331,13 +329,13 @@ impl<'a> Classifier<'a> {
 
 /// Called when we start processing a span of text that should be highlighted.
 /// The `Class` argument specifies how it should be highlighted.
-fn enter_span(out: &mut String, klass: Class) {
-    write!(out, "<span class=\"{}\">", klass.as_html()).unwrap()
+fn enter_span(out: &mut Buffer, klass: Class) {
+    write!(out, "<span class=\"{}\">", klass.as_html());
 }
 
 /// Called at the end of a span of highlighted text.
-fn exit_span(out: &mut String) {
-    write!(out, "</span>").unwrap()
+fn exit_span(out: &mut Buffer) {
+    out.write_str("</span>");
 }
 
 /// Called for a span of text. If the text should be highlighted differently
@@ -351,10 +349,10 @@ fn exit_span(out: &mut String) {
 /// ```
 /// The latter can be thought of as a shorthand for the former, which is more
 /// flexible.
-fn string<T: Display>(out: &mut String, text: T, klass: Option<Class>) {
+fn string<T: Display>(out: &mut Buffer, text: T, klass: Option<Class>) {
     match klass {
-        None => write!(out, "{}", text).unwrap(),
-        Some(klass) => write!(out, "<span class=\"{}\">{}</span>", klass.as_html(), text).unwrap(),
+        None => write!(out, "{}", text),
+        Some(klass) => write!(out, "<span class=\"{}\">{}</span>", klass.as_html(), text),
     }
 }
 

src/librustdoc/html/highlight/tests.rs

@@ -1,4 +1,5 @@
 use super::write_code;
+use crate::html::format::Buffer;
 use expect_test::expect_file;
 use rustc_span::edition::Edition;
 
@@ -18,9 +19,9 @@ const STYLE: &str = r#"
 fn test_html_highlighting() {
     let src = include_str!("fixtures/sample.rs");
     let html = {
-        let mut out = String::new();
+        let mut out = Buffer::new();
         write_code(&mut out, src, Edition::Edition2018);
-        format!("{}<pre><code>{}</code></pre>\n", STYLE, out)
+        format!("{}<pre><code>{}</code></pre>\n", STYLE, out.into_inner())
     };
     expect_file!["fixtures/sample.html"].assert_eq(&html);
 }
@@ -30,7 +31,7 @@ fn test_dos_backline() {
     let src = "pub fn foo() {\r\n\
     println!(\"foo\");\r\n\
 }\r\n";
-    let mut html = String::new();
+    let mut html = Buffer::new();
     write_code(&mut html, src, Edition::Edition2018);
-    expect_file!["fixtures/dos_line.html"].assert_eq(&html);
+    expect_file!["fixtures/dos_line.html"].assert_eq(&html.into_inner());
 }

src/librustdoc/html/markdown.rs

@@ -41,6 +41,8 @@ use pulldown_cmark::{
     html, BrokenLink, CodeBlockKind, CowStr, Event, LinkType, Options, Parser, Tag,
 };
 
+use super::format::Buffer;
+
 #[cfg(test)]
 mod tests;
 
@@ -235,9 +237,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'_, 'a, I> {
         }
         let lines = origtext.lines().filter_map(|l| map_line(l).for_html());
         let text = lines.collect::<Vec<Cow<'_, str>>>().join("\n");
-        // insert newline to clearly separate it from the
-        // previous block so we can shorten the html output
-        let mut s = String::from("\n");
+
         let playground_button = self.playground.as_ref().and_then(|playground| {
             let krate = &playground.crate_name;
             let url = &playground.url;
@@ -298,17 +298,22 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'_, 'a, I> {
             None
         };
 
-        s.push_str(&highlight::render_with_highlighting(
+        // insert newline to clearly separate it from the
+        // previous block so we can shorten the html output
+        let mut s = Buffer::new();
+        s.push_str("\n");
+        highlight::render_with_highlighting(
             &text,
+            &mut s,
             Some(&format!(
                 "rust-example-rendered{}",
                 if let Some((_, class)) = tooltip { format!(" {}", class) } else { String::new() }
             )),
             playground_button.as_deref(),
             tooltip,
             edition,
-        ));
-        Some(Event::Html(s.into()))
+        );
+        Some(Event::Html(s.into_inner().into()))
     }
 }