From 2b0f2d394fdfcc0320d03dd2acc738bee74aaa0e Mon Sep 17 00:00:00 2001
From: Alexander Wang <alex@terrastruct.com>
Date: Sat, 3 Dec 2022 00:06:59 -0800
Subject: [PATCH] add check for sequence diagram connection error

---
 d2compiler/compile_test.go                         | 12 ++++++++++++
 d2graph/d2graph.go                                 | 14 ++++++++++++++
 .../d2compiler/TestCompile/leaky_sequence.exp.json | 12 ++++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 testdata/d2compiler/TestCompile/leaky_sequence.exp.json

diff --git a/d2compiler/compile_test.go b/d2compiler/compile_test.go
index 35524f803..d4f979532 100644
--- a/d2compiler/compile_test.go
+++ b/d2compiler/compile_test.go
@@ -1520,6 +1520,18 @@ dst.id <-> src.dst_id
 				assert.String(t, "sequence_diagram", g.Root.Attributes.Shape.Value)
 			},
 		},
+		{
+			name: "leaky_sequence",
+
+			text: `x: {
+  shape: sequence_diagram
+	a
+}
+b -> x.a
+`,
+			expErr: `d2/testdata/d2compiler/TestCompile/leaky_sequence.d2:5:1: connections within sequence diagrams can connect only to other objects within the same sequence diagram
+`,
+		},
 		{
 			name: "root_direction",
 
diff --git a/d2graph/d2graph.go b/d2graph/d2graph.go
index c6a00c507..961ab0bcb 100644
--- a/d2graph/d2graph.go
+++ b/d2graph/d2graph.go
@@ -711,6 +711,16 @@ func (e *Edge) AbsID() string {
 	return fmt.Sprintf("%s(%s %s %s)[%d]", commonKey, strings.Join(srcIDA, "."), e.ArrowString(), strings.Join(dstIDA, "."), e.Index)
 }
 
+func (obj *Object) outerSequenceDiagram() *Object {
+	for obj != nil {
+		obj = obj.Parent
+		if obj.IsSequenceDiagram() {
+			return obj
+		}
+	}
+	return nil
+}
+
 func (obj *Object) Connect(srcID, dstID []string, srcArrow, dstArrow bool, label string) (*Edge, error) {
 	srcObj, srcID, err := ResolveUnderscoreKey(srcID, obj)
 	if err != nil {
@@ -732,6 +742,10 @@ func (obj *Object) Connect(srcID, dstID []string, srcArrow, dstArrow bool, label
 	src := srcObj.EnsureChild(srcID)
 	dst := dstObj.EnsureChild(dstID)
 
+	if src.outerSequenceDiagram() != dst.outerSequenceDiagram() {
+		return nil, errors.New("connections within sequence diagrams can connect only to other objects within the same sequence diagram")
+	}
+
 	edge := &Edge{
 		Attributes: Attributes{
 			Label: Scalar{
diff --git a/testdata/d2compiler/TestCompile/leaky_sequence.exp.json b/testdata/d2compiler/TestCompile/leaky_sequence.exp.json
new file mode 100644
index 000000000..182b3c4e3
--- /dev/null
+++ b/testdata/d2compiler/TestCompile/leaky_sequence.exp.json
@@ -0,0 +1,12 @@
+{
+  "graph": null,
+  "err": {
+    "ioerr": null,
+    "errs": [
+      {
+        "range": "d2/testdata/d2compiler/TestCompile/leaky_sequence.d2,4:0:36-4:8:44",
+        "errmsg": "d2/testdata/d2compiler/TestCompile/leaky_sequence.d2:5:1: connections within sequence diagrams can only connect to other objects within the same sequence diagram"
+      }
+    ]
+  }
+}