validate near key better

d2compiler/compile.go

@@ -648,21 +648,33 @@ func (c *compiler) validateKey(obj *d2graph.Object, f *d2ir.Field) {
 func (c *compiler) validateNear(g *d2graph.Graph) {
 	for _, obj := range g.Objects {
 		if obj.Attributes.NearKey != nil {
-			_, isKey := g.Root.HasChild(d2graph.Key(obj.Attributes.NearKey))
+			nearObj, isKey := g.Root.HasChild(d2graph.Key(obj.Attributes.NearKey))
 			_, isConst := d2graph.NearConstants[d2graph.Key(obj.Attributes.NearKey)[0]]
-			if !isKey && !isConst {
-				c.errorf(obj.Attributes.NearKey, "near key %#v must be the absolute path to a shape or one of the following constants: %s", d2format.Format(obj.Attributes.NearKey), strings.Join(d2graph.NearConstantsArray, ", "))
-				continue
-			}
-			if !isKey && isConst && obj.Parent != g.Root {
-				c.errorf(obj.Attributes.NearKey, "constant near keys can only be set on root level shapes")
-				continue
-			}
-			if !isKey && isConst && len(obj.ChildrenArray) > 0 {
-				c.errorf(obj.Attributes.NearKey, "constant near keys cannot be set on shapes with children")
-				continue
-			}
-			if !isKey && isConst {
+			if isKey {
+				// Doesn't make sense to set near to an ancestor or descendant
+				nearIsAncestor := false
+				for curr := obj; curr != nil; curr = curr.Parent {
+					if curr == nearObj {
+						nearIsAncestor = true
+						break
+					}
+				}
+				if nearIsAncestor {
+					c.errorf(obj.Attributes.NearKey, "near keys cannot be set to an ancestor")
+					continue
+				}
+				nearIsDescendant := false
+				for curr := nearObj; curr != nil; curr = curr.Parent {
+					if curr == obj {
+						nearIsDescendant = true
+						break
+					}
+				}
+				if nearIsDescendant {
+					c.errorf(obj.Attributes.NearKey, "near keys cannot be set to an descendant")
+					continue
+				}
+			} else if isConst {
 				is := false
 				for _, e := range g.Edges {
 					if e.Src == obj || e.Dst == obj {
@@ -674,6 +686,17 @@ func (c *compiler) validateNear(g *d2graph.Graph) {
 					c.errorf(obj.Attributes.NearKey, "constant near keys cannot be set on connected shapes")
 					continue
 				}
+				if obj.Parent != g.Root {
+					c.errorf(obj.Attributes.NearKey, "constant near keys can only be set on root level shapes")
+					continue
+				}
+				if len(obj.ChildrenArray) > 0 {
+					c.errorf(obj.Attributes.NearKey, "constant near keys cannot be set on shapes with children")
+					continue
+				}
+			} else {
+				c.errorf(obj.Attributes.NearKey, "near key %#v must be the absolute path to a shape or one of the following constants: %s", d2format.Format(obj.Attributes.NearKey), strings.Join(d2graph.NearConstantsArray, ", "))
+				continue
 			}
 		}
 	}

d2compiler/compile_test.go

@@ -1398,6 +1398,29 @@ x -> y: {
 
 			text: `x.near: top-center
 `,
+		},
+		{
+			name: "near-invalid",
+
+			text: `mongodb: MongoDB {
+  perspective: perspective (View) {
+    password
+  }
+
+  explanation: |md
+    perspective.model.js
+  | {
+    near: mongodb
+  }
+}
+
+a: {
+  near: a.b
+  b
+}
+`,
+			expErr: `d2/testdata/d2compiler/TestCompile/near-invalid.d2:9:11: near keys cannot be set to an ancestor
+d2/testdata/d2compiler/TestCompile/near-invalid.d2:14:9: near keys cannot be set to an descendant`,
 		},
 		{
 			name: "near_bad_constant",

testdata/d2compiler/TestCompile/near-invalid.exp.json

@@ -0,0 +1,16 @@
+{
+  "graph": null,
+  "err": {
+    "ioerr": null,
+    "errs": [
+      {
+        "range": "d2/testdata/d2compiler/TestCompile/near-invalid.d2,8:10:133-8:17:140",
+        "errmsg": "d2/testdata/d2compiler/TestCompile/near-invalid.d2:9:11: near keys cannot be set to an ancestor"
+      },
+      {
+        "range": "d2/testdata/d2compiler/TestCompile/near-invalid.d2,13:8:161-13:11:164",
+        "errmsg": "d2/testdata/d2compiler/TestCompile/near-invalid.d2:14:9: near keys cannot be set to an descendant"
+      }
+    ]
+  }
+}