Implement support for box-shadow shorthand

README.md

@@ -63,6 +63,8 @@ margin: 5px 7px 2px;
 
 Shorthands will only accept values that are supported in React, so `background` will only accept a colour, `backgroundColor`
 
+There is also support for the `box-shadow` shorthand, and this converts into `shadow-` properties. Note that these only work on iOS.
+
 #### Shorthand Notes
 
 `border{Top,Right,Bottom,Left}` shorthands are not supported, because `borderStyle` cannot be applied to individual border sides.

src/TokenStream.js

@@ -58,7 +58,7 @@ module.exports = class TokenStream {
     return this.throw();
   }
 
-  matchFunction() {
+  matchesFunction() {
     const node = this.node;
     if (node.type !== 'function') return null;
     const value = new TokenStream(node.nodes, node);
@@ -69,7 +69,7 @@ module.exports = class TokenStream {
   }
 
   expectFunction() {
-    const value = this.matchFunction();
+    const value = this.matchesFunction();
     if (value !== null) return value;
     return this.throw();
   }

src/index.test.js

@@ -442,6 +442,48 @@ it('does not transform invalid flex', () => {
   expect(() => transformCss([['flex', '1 2px 3']])).toThrow();
 });
 
+it('transforms box-shadow into shadow- properties', () => runTest([
+  ['box-shadow', '10px 20px 30px red'],
+], {
+  shadowOffset: { width: 10, height: 20 },
+  shadowRadius: 30,
+  shadowColor: 'red',
+}));
+
+it('transforms box-shadow without blur-radius', () => runTest([
+  ['box-shadow', '10px 20px red'],
+], {
+  shadowOffset: { width: 10, height: 20 },
+  shadowRadius: 0,
+  shadowColor: 'red',
+}));
+
+it('transforms box-shadow without color', () => runTest([
+  ['box-shadow', '10px 20px red'],
+], {
+  shadowOffset: { width: 10, height: 20 },
+  shadowRadius: 0,
+  shadowColor: 'red',
+}));
+
+it('transforms box-shadow without blur-radius, color', () => runTest([
+  ['box-shadow', '10px 20px'],
+], {
+  shadowOffset: { width: 10, height: 20 },
+  shadowRadius: 0,
+  shadowColor: 'black',
+}));
+
+it('transforms box-shadow enforces offset to be present', () => {
+  expect(() => transformCss([['box-shadow', 'red']]))
+    .toThrow('Failed to parse declaration "boxShadow: red"');
+});
+
+it('transforms box-shadow and enforces offset-y if offset-x present', () => {
+  expect(() => transformCss([['box-shadow', '10px']]))
+    .toThrow('Failed to parse declaration "boxShadow: 10px"');
+});
+
 it('allows blacklisting shorthands', () => {
   const actualStyles = transformCss([['border-radius', '50']], ['borderRadius']);
   expect(actualStyles).toEqual({ borderRadius: 50 });

src/transforms/boxShadow.js

@@ -0,0 +1,50 @@
+const { tokens } = require('../tokenTypes');
+
+const { NONE, SPACE, WORD, LENGTH } = tokens;
+
+module.exports = (tokenStream) => {
+  let offsetX;
+  let offsetY;
+  let blurRadius;
+  let color;
+
+  if (tokenStream.matches(NONE)) {
+    tokenStream.expectEmpty();
+    return {
+      $merge: { shadowOffset: { width: 0, height: 0 }, shadowRadius: 0, shadowColor: 'black' },
+    };
+  }
+
+  let didParseFirst = false;
+  while (tokenStream.hasTokens()) {
+    if (didParseFirst) tokenStream.expect(SPACE);
+
+    if (offsetX === undefined && tokenStream.matches(LENGTH)) {
+      offsetX = tokenStream.lastValue;
+      tokenStream.expect(SPACE);
+      offsetY = tokenStream.expect(LENGTH);
+
+      if (tokenStream.lookAhead().matches(LENGTH)) {
+        tokenStream.expect(SPACE);
+        blurRadius = tokenStream.expect(LENGTH);
+      }
+    } else if (color === undefined && (
+      tokenStream.matchesFunction() || tokenStream.matches(WORD)
+    )) {
+      color = String(tokenStream.lastValue);
+    } else {
+      tokenStream.throw();
+    }
+
+    didParseFirst = true;
+  }
+
+  if (offsetX === undefined) tokenStream.throw();
+
+  const $merge = {
+    shadowOffset: { width: offsetX, height: offsetY },
+    shadowRadius: blurRadius !== undefined ? blurRadius : 0,
+    shadowColor: color !== undefined ? color : 'black',
+  };
+  return { $merge };
+};

src/transforms/index.js

@@ -1,4 +1,5 @@
 const { regExpToken, tokens } = require('../tokenTypes');
+const boxShadow = require('./boxShadow');
 const flex = require('./flex');
 const font = require('./font');
 const fontFamily = require('./fontFamily');
@@ -56,6 +57,7 @@ module.exports = {
   borderColor,
   borderRadius,
   borderWidth,
+  boxShadow,
   flex,
   flexFlow,
   font,