perf(es/codegen): Reduce allocation using compact_str (#10008)

**Description:**

Previously, we allocated if there's an escape character. With this PR, we allocate if there's an escape character **and** it's long enough.

.changeset/three-nails-repair.md

@@ -0,0 +1,6 @@
+---
+swc_core: minor
+swc_ecma_codegen: minor
+---
+
+perf(es/codegen): Reduce allocation using `compact_str`

crates/swc_ecma_codegen/Cargo.toml

@@ -17,15 +17,16 @@ serde-impl = ["swc_ecma_ast/serde"]
 bench = false
 
 [dependencies]
-ascii      = { workspace = true }
-memchr     = { workspace = true }
-num-bigint = { workspace = true, features = ["serde"] }
-once_cell  = { workspace = true }
-regex      = { workspace = true }
-rustc-hash = { workspace = true }
-serde      = { workspace = true }
-sourcemap  = { workspace = true }
-tracing    = { workspace = true }
+ascii       = { workspace = true }
+compact_str = { workspace = true }
+memchr      = { workspace = true }
+num-bigint  = { workspace = true, features = ["serde"] }
+once_cell   = { workspace = true }
+regex       = { workspace = true }
+rustc-hash  = { workspace = true }
+serde       = { workspace = true }
+sourcemap   = { workspace = true }
+tracing     = { workspace = true }
 
 swc_allocator           = { version = "3.0.0", path = "../swc_allocator", default-features = false }
 swc_atoms               = { version = "3.1.0", path = "../swc_atoms" }

crates/swc_ecma_codegen/src/lib.rs

@@ -5,9 +5,10 @@
 #![allow(clippy::nonminimal_bool)]
 #![allow(non_local_definitions)]
 
-use std::{borrow::Cow, fmt::Write, io, str};
+use std::{borrow::Cow, fmt::Write, io, ops::Deref, str};
 
 use ascii::AsciiChar;
+use compact_str::{format_compact, CompactString};
 use memchr::memmem::Finder;
 use once_cell::sync::Lazy;
 use swc_allocator::maybe::vec::Vec;
@@ -108,7 +109,23 @@ where
     pub wr: W,
 }
 
-fn replace_close_inline_script(raw: &str) -> Cow<str> {
+enum CowStr<'a> {
+    Borrowed(&'a str),
+    Owned(CompactString),
+}
+
+impl Deref for CowStr<'_> {
+    type Target = str;
+
+    fn deref(&self) -> &str {
+        match self {
+            CowStr::Borrowed(s) => s,
+            CowStr::Owned(s) => s.as_str(),
+        }
+    }
+}
+
+fn replace_close_inline_script(raw: &str) -> CowStr {
     let chars = raw.as_bytes();
     let pattern_len = 8; // </script>
 
@@ -128,16 +145,16 @@ fn replace_close_inline_script(raw: &str) -> Cow<str> {
         .peekable();
 
     if matched_indexes.peek().is_none() {
-        return Cow::Borrowed(raw);
+        return CowStr::Borrowed(raw);
     }
 
-    let mut result = String::from(raw);
+    let mut result = CompactString::new(raw);
 
     for (offset, i) in matched_indexes.enumerate() {
         result.insert(i + 1 + offset, '\\');
     }
 
-    Cow::Owned(result)
+    CowStr::Owned(result)
 }
 
 static NEW_LINE_TPL_REGEX: Lazy<regex::Regex> = Lazy::new(|| regex::Regex::new(r"\\n|\n").unwrap());
@@ -684,10 +701,11 @@ where
         let (quote_char, mut value) = get_quoted_utf16(&node.value, self.cfg.ascii_only, target);
 
         if self.cfg.inline_script {
-            value = Cow::Owned(
+            value = CowStr::Owned(
                 replace_close_inline_script(&value)
                     .replace("\x3c!--", "\\x3c!--")
-                    .replace("--\x3e", "--\\x3e"),
+                    .replace("--\x3e", "--\\x3e")
+                    .into(),
             );
         }
 
@@ -3965,13 +3983,13 @@ fn get_template_element_from_raw(s: &str, ascii_only: bool) -> String {
     buf
 }
 
-fn get_ascii_only_ident(sym: &str, may_need_quote: bool, target: EsVersion) -> Cow<str> {
+fn get_ascii_only_ident(sym: &str, may_need_quote: bool, target: EsVersion) -> CowStr {
     if sym.is_ascii() {
-        return Cow::Borrowed(sym);
+        return CowStr::Borrowed(sym);
     }
 
     let mut first = true;
-    let mut buf = String::with_capacity(sym.len() + 8);
+    let mut buf = CompactString::with_capacity(sym.len() + 8);
     let mut iter = sym.chars().peekable();
     let mut need_quote = false;
 
@@ -4133,14 +4151,14 @@ fn get_ascii_only_ident(sym: &str, may_need_quote: bool, target: EsVersion) -> C
     }
 
     if need_quote {
-        Cow::Owned(format!("\"{}\"", buf))
+        CowStr::Owned(format_compact!("\"{}\"", buf))
     } else {
-        Cow::Owned(buf)
+        CowStr::Owned(buf)
     }
 }
 
 /// Returns `(quote_char, value)`
-fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> (AsciiChar, Cow<str>) {
+fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> (AsciiChar, CowStr) {
     // Fast path: If the string is ASCII and doesn't need escaping, we can avoid
     // allocation
     if v.is_ascii() {
@@ -4172,7 +4190,7 @@ fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> (AsciiChar,
             if (quote_char == AsciiChar::Apostrophe && single_quote_count == 0)
                 || (quote_char == AsciiChar::Quotation && double_quote_count == 0)
             {
-                return (quote_char, Cow::Borrowed(v));
+                return (quote_char, CowStr::Borrowed(v));
             }
         }
     }
@@ -4207,7 +4225,7 @@ fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> (AsciiChar,
 
     // Add 1 for each escaped quote
     let capacity = v.len() + escape_count;
-    let mut buf = String::with_capacity(capacity);
+    let mut buf = CompactString::with_capacity(capacity);
 
     let mut iter = v.chars().peekable();
     while let Some(c) = iter.next() {
@@ -4354,7 +4372,7 @@ fn get_quoted_utf16(v: &str, ascii_only: bool, target: EsVersion) -> (AsciiChar,
         }
     }
 
-    (quote_char, Cow::Owned(buf))
+    (quote_char, CowStr::Owned(buf))
 }
 
 fn handle_invalid_unicodes(s: &str) -> Cow<str> {

crates/swc_ecma_codegen/src/tests.rs

@@ -584,7 +584,7 @@ CONTENT\r
 
 #[test]
 fn test_get_quoted_utf16() {
-    fn combine((quote_char, s): (AsciiChar, Cow<str>)) -> String {
+    fn combine((quote_char, s): (AsciiChar, CowStr<'_>)) -> String {
         let mut new = String::with_capacity(s.len() + 2);
         new.push(quote_char.as_char());
         new.push_str(s.as_ref());