d2sequence: ensure order for child boards

d2graph/seqdiagram.go

@@ -1,6 +1,8 @@
 package d2graph
 
-import "oss.terrastruct.com/d2/d2target"
+import (
+	"oss.terrastruct.com/d2/d2target"
+)
 
 func (obj *Object) IsSequenceDiagram() bool {
 	return obj != nil && obj.Shape.Value == d2target.ShapeSequenceDiagram

d2layouts/d2sequence/sequence_diagram.go

@@ -1,9 +1,11 @@
 package d2sequence
 
 import (
+	"cmp"
 	"errors"
 	"fmt"
 	"math"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -76,6 +78,13 @@ func newSequenceDiagram(objects []*d2graph.Object, messages []*d2graph.Edge) (*s
 	var actors []*d2graph.Object
 	var groups []*d2graph.Object
 
+	slices.SortFunc(objects, func(a, b *d2graph.Object) int {
+		return cmp.Compare(getObjEarliestLineNum(a), getObjEarliestLineNum(b))
+	})
+	slices.SortFunc(messages, func(a, b *d2graph.Edge) int {
+		return cmp.Compare(getEdgeEarliestLineNum(a), getEdgeEarliestLineNum(b))
+	})
+
 	for _, obj := range objects {
 		if obj.IsSequenceDiagramGroup() {
 			queue := []*d2graph.Object{obj}

e2etests-cli/main_test.go

@@ -94,6 +94,30 @@ func TestCLI_E2E(t *testing.T) {
 				assert.TestdataDir(t, filepath.Join(dir, "layer-link"))
 			},
 		},
+		{
+			name: "sequence-layer",
+			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {
+				writeFile(t, dir, "index.d2", `k; layers: { seq: @seq.d2 }`)
+				writeFile(t, dir, "seq.d2", `shape: sequence_diagram
+a: me
+b: github.com/terrastruct/d2
+
+a -> b: issue about a bug
+a."some note about the bug"
+
+if i'm right: {
+	a <- b: fix
+}
+
+if i'm wrong: {
+	a <- b: nah, intended
+}`)
+				err := runTestMain(t, ctx, dir, env, "index.d2")
+				assert.Success(t, err)
+
+				assert.TestdataDir(t, filepath.Join(dir, "index"))
+			},
+		},
 		{
 			// Skip the empty base board so the animation doesn't show blank for 1400ms
 			name: "empty-base",