From 01322084abb82408d88a182f6b660513f7a75fa1 Mon Sep 17 00:00:00 2001
From: Natalie Weizenbaum <nweiz@google.com>
Date: Wed, 2 Aug 2023 15:23:07 -0700
Subject: [PATCH] Fix alpha unit behavior

---
 CHANGELOG.md                 |  7 ++++++-
 lib/src/functions/color.dart | 20 ++++++++++++++++++--
 test/deprecations_test.dart  |  6 ------
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 802deb5f4..3e6d4f2ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,10 +1,15 @@
 ## 1.65.0
 
+* **Breaking change**: Passing a number with unit `%` to the `$alpha` parameter
+  of `color.change()`, `color.adjust()`, `change-color()`, and `adjust-color()`
+  is now interpreted as a percentage, instead of ignoring the unit. For example,
+  `color.change(red, $alpha: 50%)` now returns `rgb(255 0 0 / 0.5)`.
+
 * Add support for CSS Color Level 4 [color spaces]. Each color value now tracks
   its color space along with the values of each channel in that color space.
   There are two general principles to keep in mind when dealing with new color
   spaces:
-  
+
   1. With the exception of legacy color spaces (`rgb`, `hsl`, and `hwb`), colors
      will always be emitted in the color space they were defined in unless
      they're explicitly converted.
diff --git a/lib/src/functions/color.dart b/lib/src/functions/color.dart
index 56322f0b7..9d2400af6 100644
--- a/lib/src/functions/color.dart
+++ b/lib/src/functions/color.dart
@@ -728,8 +728,24 @@ SassColor _changeColor(
       channelArgs[0] ?? SassNumber(color.channel0),
       channelArgs[1] ?? SassNumber(color.channel1, latterUnits),
       channelArgs[2] ?? SassNumber(color.channel2, latterUnits),
-      alphaArg.andThen(
-              (alphaArg) => _percentageOrUnitless(alphaArg, 1, 'alpha')) ??
+      alphaArg.andThen((alphaArg) {
+            if (!alphaArg.hasUnits) {
+              return alphaArg.value;
+            } else if (alphaArg.hasUnit('%')) {
+              return alphaArg.value / 100;
+            } else {
+              warnForDeprecation(
+                  "\$alpha: Passing a unit other than % ($alphaArg) is "
+                  "deprecated.\n"
+                  "\n"
+                  "To preserve current behavior: "
+                  "${alphaArg.unitSuggestion('alpha')}\n"
+                  "\n"
+                  "See https://sass-lang.com/d/function-units",
+                  Deprecation.functionUnits);
+              return alphaArg.value;
+            }
+          }) ??
           color.alpha);
 }
 
diff --git a/test/deprecations_test.dart b/test/deprecations_test.dart
index 28cd1e2fd..157963477 100644
--- a/test/deprecations_test.dart
+++ b/test/deprecations_test.dart
@@ -98,12 +98,6 @@ void main() {
       _expectDeprecation("a {b: hsl(10deg, 0%, 0)}", Deprecation.functionUnits);
     });
 
-    test("an alpha value with a percent unit", () {
-      _expectDeprecation(
-          r"@use 'sass:color'; a {b: color.change(red, $alpha: 1%)}",
-          Deprecation.functionUnits);
-    });
-
     test("an alpha value with a non-percent unit", () {
       _expectDeprecation(
           r"@use 'sass:color'; a {b: color.change(red, $alpha: 1px)}",