implement arrays for classes

ci/release/changelogs/next.md

@@ -1,5 +1,6 @@
 #### Features 🚀
 
+- `class` field now accepts arrays. See [docs](TODO). [#1256](https://github.com/terrastruct/d2/pull/1256)
 - Pill shape is implemented with rectangles of large border radius. Thanks @Poivey ! [#1006](https://github.com/terrastruct/d2/pull/1006)
 
 #### Improvements 🧹

d2compiler/compile.go

@@ -126,11 +126,25 @@ func (c *compiler) errorf(n d2ast.Node, f string, v ...interface{}) {
 func (c *compiler) compileMap(obj *d2graph.Object, m *d2ir.Map) {
 	class := m.GetField("class")
 	if class != nil {
-		className := class.Primary()
-		if className == nil {
-			c.errorf(class.LastRef().AST(), "class missing value")
+		var classNames []string
+		if class.Primary() != nil {
+			classNames = append(classNames, class.Primary().String())
+		} else if class.Composite != nil {
+			if arr, ok := class.Composite.(*d2ir.Array); ok {
+				for _, class := range arr.Values {
+					if scalar, ok := class.(*d2ir.Scalar); ok {
+						classNames = append(classNames, scalar.Value.ScalarString())
+					} else {
+						c.errorf(class.LastPrimaryKey(), "invalid value in array")
+					}
+				}
+			}
 		} else {
-			classMap := m.GetClassMap(className.String())
+			c.errorf(class.LastRef().AST(), "class missing value")
+		}
+
+		for _, className := range classNames {
+			classMap := m.GetClassMap(className)
 			if classMap != nil {
 				c.compileMap(obj, classMap)
 			}
@@ -292,7 +306,7 @@ func (c *compiler) compileLabel(attrs *d2graph.Attributes, f d2ir.Node) {
 
 func (c *compiler) compileReserved(attrs *d2graph.Attributes, f *d2ir.Field) {
 	if f.Primary() == nil {
-		if f.Composite != nil {
+		if f.Composite != nil && !strings.EqualFold(f.Name, "class") {
 			c.errorf(f.LastPrimaryKey(), "reserved field %v does not accept composite", f.Name)
 		}
 		return
@@ -462,7 +476,17 @@ func (c *compiler) compileReserved(attrs *d2graph.Attributes, f *d2ir.Field) {
 		attrs.HorizontalGap.Value = scalar.ScalarString()
 		attrs.HorizontalGap.MapKey = f.LastPrimaryKey()
 	case "class":
-		attrs.Classes = append(attrs.Classes, scalar.ScalarString())
+		if f.Primary() != nil {
+			attrs.Classes = append(attrs.Classes, scalar.ScalarString())
+		} else if f.Composite != nil {
+			if arr, ok := f.Composite.(*d2ir.Array); ok {
+				for _, class := range arr.Values {
+					if scalar, ok := class.(*d2ir.Scalar); ok {
+						attrs.Classes = append(attrs.Classes, scalar.Value.ScalarString())
+					}
+				}
+			}
+		}
 	case "classes":
 	}
 
@@ -577,11 +601,25 @@ func (c *compiler) compileEdge(obj *d2graph.Object, e *d2ir.Edge) {
 func (c *compiler) compileEdgeMap(edge *d2graph.Edge, m *d2ir.Map) {
 	class := m.GetField("class")
 	if class != nil {
-		className := class.Primary()
-		if className == nil {
-			c.errorf(class.LastRef().AST(), "class missing value")
+		var classNames []string
+		if class.Primary() != nil {
+			classNames = append(classNames, class.Primary().String())
+		} else if class.Composite != nil {
+			if arr, ok := class.Composite.(*d2ir.Array); ok {
+				for _, class := range arr.Values {
+					if scalar, ok := class.(*d2ir.Scalar); ok {
+						classNames = append(classNames, scalar.Value.ScalarString())
+					} else {
+						c.errorf(class.LastPrimaryKey(), "invalid value in array")
+					}
+				}
+			}
 		} else {
-			classMap := m.GetClassMap(className.String())
+			c.errorf(class.LastRef().AST(), "class missing value")
+		}
+
+		for _, className := range classNames {
+			classMap := m.GetClassMap(className)
 			if classMap != nil {
 				c.compileEdgeMap(edge, classMap)
 			}

d2compiler/compile_test.go

@@ -2382,6 +2382,35 @@ nostar -> 1star: { class: path }
 				tassert.Equal(t, "then", g.Edges[0].Label.Value)
 			},
 		},
+		{
+			name: "array-classes",
+			text: `classes: {
+  dragon_ball: {
+    label: ""
+    shape: circle
+    style.fill: orange
+  }
+  path: {
+    label: "then"
+    style.stroke-width: 4
+  }
+	path2: {
+    style.stroke-width: 2
+	}
+}
+nostar: { class: [dragon_ball; path] }
+1star: { class: [path; dragon_ball] }
+
+nostar -> 1star: { class: [path; path2] }
+`,
+			assertions: func(t *testing.T, g *d2graph.Graph) {
+				tassert.Equal(t, "then", g.Objects[0].Label.Value)
+				tassert.Equal(t, "", g.Objects[1].Label.Value)
+				tassert.Equal(t, "circle", g.Objects[0].Shape.Value)
+				tassert.Equal(t, "circle", g.Objects[1].Shape.Value)
+				tassert.Equal(t, "2", g.Edges[0].Style.StrokeWidth.Value)
+			},
+		},
 		{
 			name: "reordered-classes",
 			text: `classes: {

e2etests/stable_test.go

@@ -2422,6 +2422,24 @@ nostar: { class: dragon_ball }
 
 nostar -> 1star: { class: path }
 1star -> 2star: { class: path }
+`,
+		},
+		{
+			name: "array-classes",
+			script: `classes: {
+  button: {
+	  style.border-radius: 999
+		style.stroke: black
+	}
+  success: {
+	  style.fill: "#90EE90"
+	}
+  error: {
+	  style.fill: "#EA9999"
+	}
+}
+yay: Successful { class: [button; success] }
+nay: Failure { class: [button; error] }
 `,
 		},
 		{