feat: add option to only remove exact duplicate property/values

README.md

@@ -110,6 +110,40 @@ will combine into
 }
 ```
 
+In order to limit this to only combining properties when the values are equal, set the `removeDuplicatedValues` option to `true` instead. This could clean up duplicated properties, but allow for conscious duplicates such as fallbacks for custom properties.
+
+```js
+const postcss = require('postcss');
+const combineSelectors = require('postcss-combine-duplicated-selectors');
+
+postcss([combineSelectors({removeDuplicatedValues: true})]);
+```
+
+This will transform the following css
+
+```css
+.a {
+  height: 10px;
+}
+
+.a {
+  width: 20px;
+  background: var(--custom-color);
+  background: rgba(255, 165, 0, 0.5);
+}
+```
+
+into
+
+```css
+.a {
+  height: 10px;
+  width: 20px;
+  background: var(--custom-color);
+  background: rgba(255, 165, 0, 0.5);
+}
+```
+
 ### Media Queries
 
 If you have code with media queries, pass code through [_postcss-combine-media-query_](https://github.com/SassNinja/postcss-combine-media-query) or [_css-mquery-packer_](https://github.com/n19htz/css-mquery-packer) before _postcss-combine-duplicated-selectors_ to ensure optimal results.

src/index.js

@@ -38,14 +38,21 @@ function sortGroups(selector) {
 /**
  * Remove duplicated properties
  * @param {Object} selector - postcss selector node
+ * @param {Boolean} exact
  */
-function removeDupProperties(selector) {
+function removeDupProperties(selector, exact) {
   // Remove duplicated properties from bottom to top ()
   for (let actIndex = selector.nodes.length - 1; actIndex >= 1; actIndex--) {
     for (let befIndex = actIndex - 1; befIndex >= 0; befIndex--) {
       if (selector.nodes[actIndex].prop === selector.nodes[befIndex].prop) {
-        selector.nodes[befIndex].remove();
-        actIndex--;
+        if (
+          !exact ||
+          (exact &&
+            selector.nodes[actIndex].value === selector.nodes[befIndex].value)
+        ) {
+          selector.nodes[befIndex].remove();
+          actIndex--;
+        }
       }
     }
   }
@@ -79,8 +86,8 @@ module.exports = postcss.plugin(name, (options) => {
 
         // See if this query key is already in the map table
         map = mapTable.has(query) ? // If it is use it
-            mapTable.get(query) : // if not set it and get it
-            mapTable.set(query, new Map()).get(query);
+          mapTable.get(query) : // if not set it and get it
+          mapTable.set(query, new Map()).get(query);
       } else {
         // Otherwise we are dealing with a selector in the root
         map = mapTable.get('root');
@@ -100,12 +107,20 @@ module.exports = postcss.plugin(name, (options) => {
         // remove duplicated rule
         rule.remove();
 
-        if (options.removeDuplicatedProperties) {
-          removeDupProperties(destination);
+        if (options.removeDuplicatedProperties ||
+          options.removeDuplicatedValues) {
+          removeDupProperties(
+              destination,
+              options.removeDuplicatedValues,
+          );
         }
       } else {
-        if (options.removeDuplicatedProperties) {
-          removeDupProperties(rule);
+        if (options.removeDuplicatedProperties ||
+          options.removeDuplicatedValues) {
+          removeDupProperties(
+              rule,
+              options.removeDuplicatedValues,
+          );
         }
         // add new selector to symbol table
         map.set(selector, rule);

test/duplicated-properties.js

@@ -8,7 +8,7 @@ const plugin = require('../src');
  */
 
 /**
- * Take string literals are remove newlines and extra spacing so results print
+ * Take string literals and remove newlines and extra spacing so results print
  * as expected in logs
  * @return {string} string without newlines and tabs
  */
@@ -23,7 +23,7 @@ const removeDuplicates = testFactory(
 );
 
 test(
-    'remove duplicated properties when combine selectors',
+    'remove duplicated properties when combining selectors',
     removeDuplicates,
     '.a {height: 10px; color: black;} .a {color: blue; width: 20px;}',
     '.a {height: 10px;color: blue; width: 20px;}',
@@ -54,7 +54,7 @@ const keepDuplicates = testFactory(
 );
 
 test(
-    'maintain duplicated properties when combine selectors',
+    'maintain duplicated properties when combining selectors',
     keepDuplicates,
     '.a {height: 10px; color: black;} .a {color: blue; width: 20px;}',
     '.a {height: 10px; color: black;color: blue; width: 20px;}',
@@ -78,3 +78,56 @@ test(
 }
 `,
 );
+
+// Only duplicated properties with matching values should be removed
+const removeExactDuplicates = testFactory(
+    'css',
+    [plugin({removeDuplicatedValues: true})],
+);
+
+test(
+    'remove duplicated properties with matching values with combined selectors',
+    removeExactDuplicates,
+    '.a {height: 10px; color: red;} .a {color: red; color: blue; width: 20px;}',
+    '.a {height: 10px;color: red; color: blue; width: 20px;}',
+);
+
+test(
+    'remove duplicated properties with matching values in a selector',
+    removeExactDuplicates,
+    minify`
+.a {
+  height: 10px;
+  background: orange;
+  background: orange;
+  background: rgba(255, 165, 0, 0.5);
+}
+`,
+    minify`
+.a {
+  height: 10px;
+  background: orange;
+  background: rgba(255, 165, 0, 0.5);
+}
+`,
+);
+
+test(
+    'remove duplicate property with matching value, allow fallback',
+    removeExactDuplicates,
+    minify`
+.a {
+  height: 10px;
+}
+.a {
+  height: 10px;
+  height: var(--linkHeight);
+}
+`,
+    minify`
+.a {
+  height: 10px;
+  height: var(--linkHeight);
+}
+`,
+);