add analysis for MediaFeatures (#461)

closes #261

Author: bartveneman

src/atrules/atrules.test.js

@@ -624,6 +624,38 @@ AtRules('finds @media browserhacks', () => {
   assert.equal(actual, expected)
 })
 
+AtRules('finds Media Features', () => {
+  const fixture = `
+    @media (min-width: 0) {}
+    @media (max-width: 0) {}
+    @media (hover) {}
+    @media (forced-colors: none) {}
+    @media (prefers-color-scheme: dark) {}
+    @media (prefers-reduced-motion: reduce) {}
+    @media (prefers-contrast: more) {}
+
+    @media screen and (50px <= width <= 100px), (min-height: 100px) {}
+    `
+  const actual = analyze(fixture).atrules.media.features
+  const expected = {
+    total: 8,
+    totalUnique: 8,
+    unique: {
+      'min-width': 1,
+      'max-width': 1,
+      'hover': 1,
+      'forced-colors': 1,
+      'prefers-color-scheme': 1,
+      'prefers-reduced-motion': 1,
+      'prefers-contrast': 1,
+      'min-height': 1,
+    },
+    uniquenessRatio: 8 / 8,
+  }
+
+  assert.equal(actual, expected)
+})
+
 AtRules('does not crash on incomplete @media queries', () => {
   let css = `
     @media (min-width) {}

src/index.js

@@ -119,6 +119,7 @@ export function analyze(css, options = {}) {
   let imports = new Collection(useLocations)
   let medias = new Collection(useLocations)
   let mediaBrowserhacks = new Collection(useLocations)
+  let mediaFeatures = new Collection(useLocations)
   let charsets = new Collection(useLocations)
   let supports = new Collection(useLocations)
   let supportsBrowserhacks = new Collection(useLocations)
@@ -283,6 +284,10 @@ export function analyze(css, options = {}) {
         }
         break
       }
+      case 'Feature': {
+        mediaFeatures.p(node.name, node.loc)
+        break
+      }
       case Rule: {
         let prelude = node.prelude
         let block = node.block
@@ -747,6 +752,7 @@ export function analyze(css, options = {}) {
         medias.c(),
         {
           browserhacks: mediaBrowserhacks.c(),
+          features: mediaFeatures.c(),
         }
       ),
       charset: charsets.c(),

src/index.test.js

@@ -110,6 +110,12 @@ Api("handles empty input gracefully", () => {
           unique: {},
           uniquenessRatio: 0,
         },
+        features: {
+          total: 0,
+          totalUnique: 0,
+          unique: {},
+          uniquenessRatio: 0,
+        },
       },
       charset: {
         total: 0,