d2compile: invalidate self-links

ci/release/changelogs/next.md

@@ -2,4 +2,6 @@
 
 #### Improvements 🧹
 
+- Composition: links pointing to own board are purged [#2203](https://github.com/terrastruct/d2/pull/2203)
+
 #### Bugfixes ⛑️

d2compiler/compile.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"io/fs"
 	"net/url"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -1224,6 +1225,11 @@ func (c *compiler) validateBoardLinks(g *d2graph.Graph) {
 			obj.Link = nil
 			continue
 		}
+
+		if slices.Equal(linkKey.IDA(), obj.Graph.IDA()) {
+			obj.Link = nil
+			continue
+		}
 	}
 	for _, b := range g.Layers {
 		c.validateBoardLinks(b)

d2compiler/compile_test.go

@@ -2317,6 +2317,27 @@ scenarios: {
 				tassert.Equal(t, "root.layers.cat", g.Scenarios[0].Objects[0].Link.Value)
 			},
 		},
+		{
+			name: "no-self-link",
+			text: `
+x.link: scenarios.a
+
+layers: {
+  g: {
+    s.link: _.layers.g
+  }
+}
+
+scenarios: {
+  a: {
+    b
+  }
+}`,
+			assertions: func(t *testing.T, g *d2graph.Graph) {
+				tassert.Equal(t, (*d2graph.Scalar)(nil), g.Scenarios[0].Objects[0].Link)
+				tassert.Equal(t, (*d2graph.Scalar)(nil), g.Layers[0].Objects[0].Link)
+			},
+		},
 		{
 			name: "link-board-not-found-1",
 			text: `x.link: layers.x

d2graph/d2graph.go

@@ -84,6 +84,66 @@ func (g *Graph) RootBoard() *Graph {
 	return g
 }
 
+func (g *Graph) IDA() []string {
+	if g == nil {
+		return nil
+	}
+
+	var parts []string
+
+	current := g
+	for current != nil {
+		if current.Name != "" {
+			parts = append(parts, current.Name)
+		}
+		current = current.Parent
+	}
+
+	for i := 0; i < len(parts)/2; i++ {
+		j := len(parts) - 1 - i
+		parts[i], parts[j] = parts[j], parts[i]
+	}
+
+	if len(parts) == 0 {
+		return []string{"root"}
+	}
+
+	parts = append([]string{"root"}, parts...)
+
+	if g.Parent != nil {
+		var containerName string
+		if len(g.Parent.Layers) > 0 {
+			for _, l := range g.Parent.Layers {
+				if l == g {
+					containerName = "layers"
+					break
+				}
+			}
+		}
+		if len(g.Parent.Scenarios) > 0 {
+			for _, s := range g.Parent.Scenarios {
+				if s == g {
+					containerName = "scenarios"
+					break
+				}
+			}
+		}
+		if len(g.Parent.Steps) > 0 {
+			for _, s := range g.Parent.Steps {
+				if s == g {
+					containerName = "steps"
+					break
+				}
+			}
+		}
+		if containerName != "" {
+			parts = append(parts[:1], append([]string{containerName}, parts[1:]...)...)
+		}
+	}
+
+	return parts
+}
+
 type LayoutGraph func(context.Context, *Graph) error
 type RouteEdges func(context.Context, *Graph, []*Edge) error