Ensure interleave nested declarations have a semicolon when needed

Closes #1089

Author: devongovett

src/lib.rs

@@ -24929,6 +24929,21 @@ mod tests {
         exclude: Features::empty(),
       },
     );
+
+    minify_test(
+      r#"
+    .foo {
+      color: red;
+      .bar {
+        color: green;
+      }
+      color: blue;
+      .baz {
+        color: pink;
+      }
+    }"#,
+      ".foo{color:red;& .bar{color:green}color:#00f;& .baz{color:pink}}",
+    );
   }
 
   #[test]

src/rules/mod.rs

@@ -1025,7 +1025,7 @@ impl<'a, 'i, T: ToCss> ToCss for CssRuleList<'i, T> {
     let mut first = true;
     let mut last_without_block = false;
 
-    for rule in &self.0 {
+    for (i, rule) in self.0.iter().enumerate() {
       if let CssRule::Ignored = &rule {
         continue;
       }
@@ -1061,6 +1061,12 @@ impl<'a, 'i, T: ToCss> ToCss for CssRuleList<'i, T> {
         dest.newline()?;
       }
       rule.to_css(dest)?;
+
+      // If this is an invisible nested declarations rule, and not the last rule in the block, add a semicolon.
+      if dest.minify && matches!(rule, CssRule::NestedDeclarations(_)) && i != self.0.len() - 1 {
+        dest.write_char(';')?;
+      }
+
       last_without_block = matches!(
         rule,
         CssRule::Import(..) | CssRule::Namespace(..) | CssRule::LayerStatement(..)