feat(css/minifier): Remove adjacent identical declarations (#6619)

crates/swc_css_minifier/src/compressor/declaration.rs

@@ -343,18 +343,18 @@ impl Compressor {
                             ComponentValue::Ident(box Ident { value, span, .. })
                                 if value.eq_ignore_ascii_case(&js_word!("normal")) =>
                             {
-                                ComponentValue::Number(Box::new(Number {
+                                ComponentValue::Integer(Box::new(Integer {
                                     span,
-                                    value: 400.0,
+                                    value: 400,
                                     raw: None,
                                 }))
                             }
                             ComponentValue::Ident(box Ident { value, span, .. })
                                 if value.eq_ignore_ascii_case(&js_word!("bold")) =>
                             {
-                                ComponentValue::Number(Box::new(Number {
+                                ComponentValue::Integer(Box::new(Integer {
                                     span,
-                                    value: 700.0,
+                                    value: 700,
                                     raw: None,
                                 }))
                             }

crates/swc_css_minifier/src/compressor/rules.rs

@@ -58,6 +58,13 @@ impl Compressor {
         }
     }
 
+    fn get_declaration_name(&self, declaration: &Declaration) -> JsWord {
+        match &declaration.name {
+            DeclarationName::Ident(Ident { value, .. }) => value.to_ascii_lowercase(),
+            DeclarationName::DashedIdent(DashedIdent { value, .. }) => value.to_ascii_lowercase(),
+        }
+    }
+
     fn collect_names(&self, at_rule: &AtRule, names: &mut AHashMap<Name, isize>) {
         match &at_rule.prelude {
             Some(box AtRulePrelude::CounterStylePrelude(CustomIdent { value: name, .. })) => {
@@ -532,6 +539,18 @@ impl Compressor {
 
                     true
                 }
+                ComponentValue::Declaration(box declaration) if prev_rule.is_some() => {
+                    if let Some(ComponentValue::Declaration(box prev_rule)) = &mut prev_rule {
+                        if self.get_declaration_name(prev_rule)
+                            == self.get_declaration_name(declaration)
+                            && prev_rule.value.eq_ignore_span(&declaration.value)
+                        {
+                            remove_rules_list.push(prev_index);
+                        }
+                    }
+
+                    true
+                }
                 _ => {
                     if let ComponentValue::AtRule(rule) = rule {
                         self.collect_names(rule, &mut names);
@@ -547,11 +566,14 @@ impl Compressor {
                         prev_index = index;
                         prev_rule_idx = Some(index);
                     }
-
                     ComponentValue::QualifiedRule(_) => {
                         prev_index = index;
                         prev_rule_idx = Some(index);
                     }
+                    ComponentValue::Declaration(_) => {
+                        prev_index = index;
+                        prev_rule_idx = Some(index);
+                    }
                     _ => {
                         prev_rule_idx = None;
                     }

crates/swc_css_minifier/tests/fixture/compress-declaration/duplication/input.css

@@ -0,0 +1,108 @@
+a {
+    color: red;
+    color: red;
+
+    .class {
+        color: red;
+        color: red;
+    }
+
+    @media screen and (min-width: 100px) {
+        color: red;
+        color: red;
+    }
+
+    @supports (display: flex) {
+        color: red;
+        color: red;
+
+        .other {
+            color: red;
+            color: red;
+        }
+    }
+
+    .case-insensitivity {
+        color: red;
+        COLOR: red;
+    }
+}
+
+.font {
+    > h1 { font-weight: bold }
+    > h1 { font-weight: 700 }
+}
+
+.class {
+    > h1 { font-weight: bold }
+    > h1 { font-weight: bold }
+}
+
+.other {
+    > h1 { font-weight: 700 }
+    > h1 { font-weight: 700 }
+}
+
+.base {
+    color: red;
+
+    .class {
+        color: red;
+    }
+
+    .class-other {
+        color: red;
+    }
+
+    @media screen {
+        .class {
+            color: red;
+        }
+
+        .class-other {
+            color: red;
+        }
+    }
+}
+
+h1{/*test*/font-weight:bold}
+h1{/*test*/font-weight:bold}
+
+.white {
+    _color:white;
+    color:white
+}
+
+h1,h2{font-weight:bold}
+h2,h1{font-weight:bold}
+
+.margin{margin:10px 0 10px 0;margin:10px 0}
+
+h1{font-weight:bold;font-weight:bold}
+h1{font-weight:bold}
+
+@media print{
+    h1 {
+        display:block
+    }
+}
+@media print{
+    h1 {
+        display:block
+    }
+}
+
+.other {
+    & h1 { font-weight: bold }
+    & h1 { font-weight: bold }
+}
+
+@media print{
+    h1, h2 {
+        font-weight:bold
+    }
+
+    h2, h1{
+        font-weight:bold
+    }
+}

crates/swc_css_minifier/tests/fixture/compress-declaration/font-weight/output.min.css

@@ -1 +1 @@
-.class1{font-weight:1;font-weight:400;font-weight:1000}.class2{font-weight:400}.class3{font-weight:700;font-weight:700}.class4{font-weight:400 700}.class5{font-weight:600 700}
+.class1{font-weight:1;font-weight:400;font-weight:1000}.class2{font-weight:400}.class3{font-weight:700}.class4{font-weight:400 700}.class5{font-weight:600 700}