Stabilize repeated layout block IDs

edge_test.go

@@ -496,6 +496,19 @@ func TestLayout_DuplicateVariantChars_Ugly(t *testing.T) {
 	}
 }
 
+func TestLayout_DuplicateVariantChars_UniqueBlockIDs_Good(t *testing.T) {
+	ctx := NewContext()
+
+	layout := NewLayout("CCC").C(Raw("content"))
+	got := layout.Render(ctx)
+
+	for _, want := range []string{`data-block="C"`, `data-block="C.1"`, `data-block="C.2"`} {
+		if !containsText(got, want) {
+			t.Fatalf("CCC variant should assign unique block ID %q, got:\n%s", want, got)
+		}
+	}
+}
+
 func TestLayout_EmptySlots_Ugly(t *testing.T) {
 	ctx := NewContext()
 

layout.go

@@ -180,6 +180,7 @@ func (l *Layout) Render(ctx *Context) string {
 
 	b := newTextBuilder()
 	rendered := 0
+	rootCounts := make(map[byte]int)
 
 	for i := range len(l.variant) {
 		slot := l.variant[i]
@@ -194,6 +195,12 @@ func (l *Layout) Render(ctx *Context) string {
 		}
 
 		bid := l.blockID(slot, rendered)
+		if l.path == "" {
+			if seen := rootCounts[slot]; seen > 0 {
+				bid = string(slot) + "." + strconv.Itoa(seen)
+			}
+			rootCounts[slot] = rootCounts[slot] + 1
+		}
 
 		b.WriteByte('<')
 		b.WriteString(escapeHTML(meta.tag))