validate gradient color stops

d2compiler/compile_test.go

@@ -3929,6 +3929,14 @@ svc_1.t2 -> b: do with B
 				tassert.Equal(t, "d2/testdata/d2compiler/TestCompile/meow.d2", g.Layers[0].Layers[0].AST.Range.Path)
 			},
 		},
+		{
+			name: "invalid_gradient_color_stop",
+			text: `
+				x
+				x.style.fill: "linear-gradient(#ggg, #000)"
+			`,
+			expErr: `d2/testdata/d2compiler/TestCompile/invalid_gradient_color_stop.d2:3:19: expected "fill" to be a valid named color ("orange"), a hex code ("#f0ff3a"), or a gradient ("linear-gradient(red, blue)")`,
+		},
 	}
 
 	for _, tc := range testCases {

lib/color/gradient.go

@@ -9,6 +9,8 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+
+	"github.com/mazznoer/csscolorparser"
 )
 
 type Gradient struct {
@@ -241,10 +243,15 @@ func UniqueGradientID(cssGradient string) string {
 	return "grad-" + hash
 }
 
-var GradientRegex = regexp.MustCompile(`^(linear|radial)-gradient\((.+)\)$`)
-
 func IsGradient(color string) bool {
-	return GradientRegex.MatchString(color)
+	gradient, err := ParseGradient(color)
+	for _, colorStop := range gradient.ColorStops {
+		_, err = csscolorparser.Parse(colorStop.Color)
+		if err != nil {
+			break
+		}
+	}
+	return err == nil
 }
 
 var URLGradientID = regexp.MustCompile(`^url\('#grad-[a-f0-9]{40}'\)$`)