fix: choose shorter quotes for minified URLs (#7)

Co-authored-by: Cong-Cong Pan <dacongsama@live.com>

Author: intellild

src/lib.rs

@@ -32470,6 +32470,76 @@ mod tests {
 
   #[test]
   fn test_quoting_unquoting_urls() {
+    // Single quotes avoid escaping the double quotes in SVG attributes.
+    minify_test(
+      r#"
+      .foo {
+        background-image: url('data:image/svg+xml,<svg width="1" height="1"></svg>');
+      }
+      "#,
+      r#".foo{background-image:url('data:image/svg+xml,<svg width="1" height="1"></svg>')}"#,
+    );
+
+    // Keep double quotes when they are shorter or tied with single quotes.
+    minify_test(
+      r#"
+      .foo {
+        background-image: url("a 'b' c"), url('a "b" \'c\''), url('a "b" \'c');
+      }
+      "#,
+      r#".foo{background-image:url("a 'b' c"),url("a \"b\" 'c'"),url('a "b" \'c')}"#,
+    );
+
+    // Unquoted output still wins ties, including an empty URL.
+    minify_test(
+      r#"
+      .foo {
+        background-image: url('"'), url('""'), url('"""'), url('');
+      }
+      "#,
+      r#".foo{background-image:url(\"),url(\"\"),url('"""'),url()}"#,
+    );
+
+    // Escaped quotes and backslashes are parsed before choosing the quote style.
+    minify_test(
+      r#"
+      .foo {
+        background-image: url("a \\\"b\\\" \\c"), url('a "b" \\\'c');
+      }
+      "#,
+      r#".foo{background-image:url('a \\"b\\" \\c'),url('a "b" \\\'c')}"#,
+    );
+
+    // Preserve control characters and hex escape terminators before hex digits and spaces.
+    minify_test(
+      r#"
+      .foo {
+        background-image: url('"a"\a f\d  \c a\1 b\7f c\9 "é😀"');
+      }
+      "#,
+      r#".foo{background-image:url('"a"\a f\d  \c a\1 b\7f c\9 "é😀"')}"#,
+    );
+
+    minify_test(
+      r#"
+      .foo {
+        background-image: url('"a" \
+b\0 c');
+      }
+      "#,
+      r#".foo{background-image:url('"a" b�c')}"#,
+    );
+
+    // Keep the existing double-quoted output when not minifying.
+    test(
+      r#"
+      .foo {
+        background-image: url('a "b" c');
+      }
+      "#,
+      ".foo {\n  background-image: url(\"a \\\"b\\\" c\");\n}\n",
+    );
+
     // Quotes remain double quotes when not minifying
     test(
       r#".foo {
@@ -32509,6 +32579,99 @@ mod tests {
     );
   }
 
+  #[test]
+  fn test_url_quote_roundtrip() {
+    use crate::values::url::Url;
+
+    // Exercise escape boundaries on both sides of quotes, including a literal
+    // backslash followed by a hex digit and non-ASCII text.
+    let parts = [
+      "\"", "'", "\\", "\n", "\r", "\x0c", "\x01", "\x7f", "\t", " ", "f", "é😀", "(", ")",
+    ];
+    for a in parts {
+      for b in parts {
+        for c in parts {
+          let value = format!("\"\"{a}{b}{c}\"\"");
+          let url = Url {
+            url: value.as_str().into(),
+            loc: crate::dependencies::Location { line: 1, column: 1 },
+          };
+          let serialized = url
+            .to_css_string(PrinterOptions {
+              minify: true,
+              ..Default::default()
+            })
+            .unwrap();
+          assert_eq!(Url::parse_string(&serialized).unwrap(), url);
+        }
+      }
+    }
+  }
+
+  #[test]
+  fn test_url_quoting_dependencies() {
+    let stylesheet = StyleSheet::parse(
+      r#"
+      .foo {
+        background-image: url('a "b" c');
+      }
+      "#,
+      ParserOptions::default(),
+    )
+    .unwrap();
+    let result = stylesheet
+      .to_css(
+        PrinterOptions {
+          minify: true,
+          analyze_dependencies: Some(Default::default()),
+          ..Default::default()
+        },
+        None::<&mut ()>,
+      )
+      .unwrap();
+    let dependencies = result.dependencies.unwrap();
+    assert_eq!(dependencies.len(), 1);
+    let Dependency::Url(dep) = &dependencies[0] else {
+      panic!("expected URL dependency")
+    };
+    assert_eq!(dep.url, r#"a "b" c"#);
+    assert_eq!(
+      result.code,
+      format!(".foo{{background-image:url(\"{}\")}}", dep.placeholder)
+    );
+  }
+
+  #[test]
+  #[cfg(feature = "sourcemap")]
+  fn test_url_quoting_source_map() {
+    let stylesheet = StyleSheet::parse(
+      r#"
+      .foo {
+        background-image: url('"a" \a b');
+      }
+      .bar {
+        color: red;
+      }
+      "#,
+      ParserOptions::default(),
+    )
+    .unwrap();
+    let mut sm = parcel_sourcemap::SourceMap::new("/");
+    let result = stylesheet
+      .to_css(
+        PrinterOptions {
+          minify: true,
+          ..Default::default()
+        },
+        Some(&mut sm),
+      )
+      .unwrap();
+    let column = result.code.find(".bar").unwrap() as u32;
+    let mapping = sm.find_closest_mapping(0, column).unwrap();
+    assert_eq!(mapping.generated_column, column);
+    assert_eq!(mapping.original.unwrap().original_line, 4);
+  }
+
   #[test]
   fn test_zindex() {
     minify_test(".foo { z-index: 2 }", ".foo{z-index:2}");

src/values/url.rs

@@ -7,6 +7,7 @@ use crate::values::string::CowArcStr;
 #[cfg(feature = "visitor")]
 use crate::visitor::Visit;
 use cssparser::*;
+use std::fmt::{self, Write};
 
 /// A CSS [url()](https://www.w3.org/TR/css-values-4/#urls) value and its source location.
 #[derive(Debug, Clone)]
@@ -64,11 +65,25 @@ impl<'i> ToCss for Url<'i> {
       let mut buf = String::new();
       Token::UnquotedUrl(CowRcStr::from(self.url.as_ref())).to_css(&mut buf)?;
 
-      // If the unquoted url is longer than it would be quoted (e.g. `url("...")`)
-      // then serialize as a string and choose the shorter version.
+      // If quoting could be shorter, choose the quote that needs fewer escapes,
+      // then compare with the unquoted url. Keep the existing choice on ties.
       if buf.len() > self.url.len() + 7 {
+        let mut single_quotes = 0;
+        let mut double_quotes = 0;
+        for b in self.url.bytes() {
+          match b {
+            b'\'' => single_quotes += 1,
+            b'"' => double_quotes += 1,
+            _ => {}
+          }
+        }
+
         let mut buf2 = String::new();
-        serialize_string(&self.url, &mut buf2)?;
+        if double_quotes > single_quotes {
+          serialize_single_quoted_string(&self.url, &mut buf2)?;
+        } else {
+          serialize_string(&self.url, &mut buf2)?;
+        }
         if buf2.len() + 5 < buf.len() {
           dest.write_str("url(")?;
           dest.write_str(&buf2)?;
@@ -88,6 +103,24 @@ impl<'i> ToCss for Url<'i> {
   }
 }
 
+fn serialize_single_quoted_string<W: Write>(value: &str, dest: &mut W) -> fmt::Result {
+  dest.write_char('\'')?;
+  let mut start = 0;
+  for (i, b) in value.bytes().enumerate() {
+    if matches!(b, b'\'' | b'"') {
+      // Delegate all other escapes, including hex escape terminators, to cssparser.
+      CssStringWriter::new(dest).write_str(&value[start..i])?;
+      if b == b'\'' {
+        dest.write_char('\\')?;
+      }
+      dest.write_char(b as char)?;
+      start = i + 1;
+    }
+  }
+  CssStringWriter::new(dest).write_str(&value[start..])?;
+  dest.write_char('\'')
+}
+
 impl<'i> Url<'i> {
   /// Returns whether the URL is absolute, and not relative.
   pub fn is_absolute(&self) -> bool {