Add a fast-path to Debug ASCII &str

Instead of going through the `EscapeDebug` machinery, we can just skip over ASCII chars that don’t need any escaping.
rust-lang · Feb 15, 2024 · 04602a2 · 04602a2
1 parent bd6b336
commit 04602a2
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
@@ -2340,6 +2340,11 @@ impl Debug for str {
         f.write_char('"')?;
         let mut from = 0;
         for (i, c) in self.char_indices() {
+            // a fast path for ASCII chars that do not need escapes:
+            if matches!(c, ' '..='~') && !matches!(c, '\\' | '\"') {
+                continue;
+            }
+
             let esc = c.escape_debug_ext(EscapeDebugExtArgs {
                 escape_grapheme_extended: true,
                 escape_single_quote: false,