fix disconnected edge with dagre layout in direction right

ci/release/changelogs/next.md

@@ -10,3 +10,4 @@
 - Fixes missing unfilled triangle arrowheads when sketch flag is on. [#1763](https://github.com/terrastruct/d2/pull/1763)
 - Fixes a bug where the render target could be incorrect if the target path contains "index". [#1764](https://github.com/terrastruct/d2/pull/1764)
 - Fixes ELK layout with outside labels/icons. [#1776](https://github.com/terrastruct/d2/pull/1776)
+- Fixes a bug where an edge could become disconnected with dagre layout and direction right. [#1778](https://github.com/terrastruct/d2/pull/1778)

d2layouts/d2dagrelayout/layout.go

@@ -902,14 +902,27 @@ func shiftReachableDown(g *d2graph.Graph, obj *d2graph.Object, start, distance f
 						}
 					}
 					queue(e.Dst)
+					first := e.Route[0]
+					startIndex := 0
+					_, wasShifted := shifted[curr]
 					if isHorizontal {
-						for _, p := range e.Route {
+						if wasShifted && first.X < curr.TopLeft.X && first.X < start {
+							first.X += distance
+							startIndex++
+						}
+						for i := startIndex; i < len(e.Route); i++ {
+							p := e.Route[i]
 							if start <= p.X {
 								p.X += distance
 							}
 						}
 					} else {
-						for _, p := range e.Route {
+						if wasShifted && first.Y < curr.TopLeft.Y && first.Y < start {
+							first.Y += distance
+							startIndex++
+						}
+						for i := startIndex; i < len(e.Route); i++ {
+							p := e.Route[i]
 							if start <= p.Y {
 								p.Y += distance
 							}
@@ -930,14 +943,27 @@ func shiftReachableDown(g *d2graph.Graph, obj *d2graph.Object, start, distance f
 						}
 					}
 					queue(e.Src)
+					last := e.Route[len(e.Route)-1]
+					endIndex := len(e.Route)
+					_, wasShifted := shifted[curr]
 					if isHorizontal {
-						for _, p := range e.Route {
+						if wasShifted && last.X < curr.TopLeft.X && last.X < start {
+							last.X += distance
+							endIndex--
+						}
+						for i := 0; i < endIndex; i++ {
+							p := e.Route[i]
 							if start <= p.X {
 								p.X += distance
 							}
 						}
 					} else {
-						for _, p := range e.Route {
+						if wasShifted && last.Y < curr.TopLeft.Y && last.Y < start {
+							last.Y += distance
+							endIndex--
+						}
+						for i := 0; i < endIndex; i++ {
+							p := e.Route[i]
 							if start <= p.Y {
 								p.Y += distance
 							}

e2etests/regression_test.go

@@ -1053,6 +1053,7 @@ cf many required: {
 		loadFromFile(t, "shaped_grid_positioning"),
 		loadFromFile(t, "cloud_shaped_grid"),
 		loadFromFileWithOptions(t, "nested_layout_bug", testCase{testSerialization: true}),
+		loadFromFile(t, "disconnect_direction_right"),
 	}
 
 	runa(t, tcs)

e2etests/testdata/files/disconnect_direction_right.d2

@@ -0,0 +1,16 @@
+direction: right
+
+a: {
+  b
+}
+
+c: {
+  d
+}
+
+e: {
+  f
+}
+
+a.b -> c.d
+a.b -> e.f