render: elk trace to shape border

ci/release/changelogs/next.md

@@ -14,5 +14,6 @@
 - Fixed crash when sequence diagrams had no messages. [https://github.com/terrastruct/d2/pull/427](https://github.com/terrastruct/d2/pull/427)
 - Fixed `constraint` keyword setting label. [https://github.com/terrastruct/d2/issues/415](https://github.com/terrastruct/d2/issues/415)
 - Fixed serialization affecting binary plugins (TALA). [https://github.com/terrastruct/d2/pull/426](https://github.com/terrastruct/d2/pull/426)
+- Fixed connections in elk layouts not going all the way to shape borders. [https://github.com/terrastruct/d2/pull/459](https://github.com/terrastruct/d2/pull/459)
 - Fixed a connection rendering bug that could happen in firefox when there were no connection labels. [https://github.com/terrastruct/d2/pull/453](https://github.com/terrastruct/d2/pull/453)
 - Fixed a crash when external connection IDs were prefixes of a sequence diagram ID. [https://github.com/terrastruct/d2/pull/462](https://github.com/terrastruct/d2/pull/462)

d2layouts/d2elklayout/layout.go

@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"math"
+	"strings"
 
 	"github.com/dop251/goja"
 
@@ -21,6 +22,7 @@ import (
 	"oss.terrastruct.com/d2/d2target"
 	"oss.terrastruct.com/d2/lib/geo"
 	"oss.terrastruct.com/d2/lib/label"
+	"oss.terrastruct.com/d2/lib/shape"
 )
 
 //go:embed elk.js
@@ -289,6 +291,14 @@ func Layout(ctx context.Context, g *d2graph.Graph) (err error) {
 			})
 		}
 
+		startIndex, endIndex := 0, len(points)-1
+		srcShape := shape.NewShape(d2target.DSL_SHAPE_TO_SHAPE_TYPE[strings.ToLower(edge.Src.Attributes.Shape.Value)], edge.Src.Box)
+		dstShape := shape.NewShape(d2target.DSL_SHAPE_TO_SHAPE_TYPE[strings.ToLower(edge.Dst.Attributes.Shape.Value)], edge.Dst.Box)
+
+		// trace the edge to the specific shape's border
+		points[startIndex] = shape.TraceToShapeBorder(srcShape, points[startIndex], points[startIndex+1])
+		points[endIndex] = shape.TraceToShapeBorder(dstShape, points[endIndex], points[endIndex-1])
+
 		if edge.Attributes.Label.Value != "" {
 			edge.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
 		}