Add deprecation warnings for hex alpha colors

Also support unambiguous hex alpha colors.

Closes #360
See sass/sass#2179

CHANGELOG.md

@@ -1,4 +1,10 @@
-## 1.6.3
+## 1.7.0
+
+* Emit deprecation warnings for tokens such as `#abcd` that are ambiguous
+  between ID strings and hex colors with alpha channels. These will be
+  interpreted as colors in a release on or after 19 September 2018.
+
+* Parse unambiguous hex colors with alpha channels as colors.
 
 * Fix a bug where relative imports from files on the load path could look in the
   incorrect location.

lib/src/parse/stylesheet.dart

@@ -1742,7 +1742,20 @@ abstract class StylesheetParser extends Parser {
     var identifier = _interpolatedIdentifier();
     if (_isHexColor(identifier)) {
       scanner.state = afterHash;
-      return new ColorExpression(_hexColorContents(start));
+      var color = _hexColorContents(start);
+
+      var plain = identifier.asPlain;
+      if (plain.length == 4 || plain.length == 8) {
+        logger.warn('''
+The value "$color" is currently parsed as a string, but it will be parsed as a
+color in a release on or after 19 September 2018.
+
+To continue parsing it as a string, use "unquote('$color')".
+To parse it as a color, use "${color.toStringAsRgb()}".
+''', span: color.originalSpan, deprecation: true);
+      } else {
+        return new ColorExpression(color);
+      }
     }
 
     var buffer = new InterpolationBuffer();
@@ -1753,30 +1766,52 @@ abstract class StylesheetParser extends Parser {
 
   /// Consumes the contents of a hex color, after the `#`.
   SassColor _hexColorContents(LineScannerState start) {
-    var red = _hexDigit();
-    var green = _hexDigit();
-    var blue = _hexDigit();
-
-    var next = scanner.peekChar();
-    if (next != null && isHex(next)) {
-      red = (red << 4) + green;
-      green = (blue << 4) + _hexDigit();
-      blue = (_hexDigit() << 4) + _hexDigit();
+    var digit1 = _hexDigit();
+    var digit2 = _hexDigit();
+    var digit3 = _hexDigit();
+
+    int red;
+    int green;
+    int blue;
+    num alpha = 1;
+    if (!isHex(scanner.peekChar())) {
+      // #abc
+      red = (digit1 << 4) + digit1;
+      green = (digit2 << 4) + digit2;
+      blue = (digit3 << 4) + digit3;
     } else {
-      red = (red << 4) + red;
-      green = (green << 4) + green;
-      blue = (blue << 4) + blue;
+      var digit4 = _hexDigit();
+      if (!isHex(scanner.peekChar())) {
+        // #abcd
+        red = (digit1 << 4) + digit1;
+        green = (digit2 << 4) + digit2;
+        blue = (digit3 << 4) + digit3;
+        alpha = ((digit4 << 4) + digit4) / 0xff;
+      } else {
+        red = (digit1 << 4) + digit2;
+        green = (digit3 << 4) + digit4;
+        blue = (_hexDigit() << 4) + _hexDigit();
+
+        if (isHex(scanner.peekChar())) {
+          alpha = ((_hexDigit() << 4) + _hexDigit()) / 0xff;
+        }
+      }
     }
 
-    return new SassColor.rgb(red, green, blue, 1, scanner.spanFrom(start));
+    return new SassColor.rgb(red, green, blue, alpha, scanner.spanFrom(start));
   }
 
   /// Returns whether [interpolation] is a plain string that can be parsed as a
   /// hex color.
   bool _isHexColor(Interpolation interpolation) {
     var plain = interpolation.asPlain;
     if (plain == null) return false;
-    if (plain.length != 3 && plain.length != 6) return false;
+    if (plain.length != 3 &&
+        plain.length != 4 &&
+        plain.length != 6 &&
+        plain.length != 8) {
+      return false;
+    }
     return plain.codeUnits.every(isHex);
   }
 

lib/src/util/character.dart

@@ -43,10 +43,13 @@ bool isName(int character) =>
     isNameStart(character) || isDigit(character) || character == $minus;
 
 /// Returns whether [character] is a hexadeicmal digit.
-bool isHex(int character) =>
-    isDigit(character) ||
-    (character >= $a && character <= $f) ||
-    (character >= $A && character <= $F);
+bool isHex(int character) {
+  if (character == null) return false;
+  if (isDigit(character)) return true;
+  if (character >= $a && character <= $f) return true;
+  if (character >= $A && character <= $F) return true;
+  return false;
+}
 
 /// Returns whether [character] is the beginning of a UTF-16 surrogate pair.
 bool isHighSurrogate(int character) =>

lib/src/value/color.dart

@@ -201,4 +201,20 @@ class SassColor extends Value implements ext.SassColor {
 
     return fuzzyRound(result * 255);
   }
+
+  /// Returns an `rgb()` or `rgba()` function call that will evaluate to this
+  /// color.
+  String toStringAsRgb() {
+    var isOpaque = fuzzyEquals(alpha, 1);
+    var buffer = new StringBuffer(isOpaque ? "rgb" : "rgba")
+      ..write("($red, $green, $blue");
+
+    if (!isOpaque) {
+      // Write the alpha as a SassNumber to ensure it's valid CSS.
+      buffer.write(", ${new SassNumber(alpha)}");
+    }
+
+    buffer.write(")");
+    return buffer.toString();
+  }
 }

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.6.3-dev
+version: 1.7.0
 description: A Sass implementation in Dart.
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/sass/dart-sass