Tests: gate the allocations a reference path costs across a repeat and in a named draw group

perf_test.go

@@ -52,6 +52,32 @@ func TestNoRenderAllocRegression(t *testing.T) {
 }
 
 // A record's fences read the compiled tree, so they belong to New, not to a draw.
+// A reference path read across a repeat, and one read in a named draw group. The repeat
+// prices both measures that keep a render's draw set off the heap — inlining expandAnew
+// into render's loop, or keying a draw group's map with the scope's own string, costs an
+// allocation an iteration — while the draw group holds the group path's own count.
+func TestNoReferenceAllocRegression(t *testing.T) {
+	word := `{"format":"{w}","w":["alpha","beta","gamma","delta"]}`
+	for _, s := range []struct {
+		name, json string
+		base       float64
+	}{
+		{"a repeat of a reference path", `{"format":"{r}","r":{"format":"{/word.w}","repeat":20,"separator":", "}}`, 66},
+		{"a named draw group", `{"format":"{a}","a":{"format":"{/word.w}","drawGroup":"g"}}`, 11},
+	} {
+		f, err := New(WithoutShippedData(), WithDataFS(fstest.MapFS{
+			"word.json": {Data: []byte(word)},
+			"x.json":    {Data: []byte(s.json)},
+		}))
+		if err != nil {
+			t.Fatalf("New(%s): %v", s.name, err)
+		}
+		if allocs := testing.AllocsPerRun(10000, func() { f.Fake("x") }); allocs > s.base*1.10 {
+			t.Errorf("%s: %.1f allocs/op regressed past %.1f (baseline %.1f + 10%%); a draw set reaching the heap is the usual cause", s.name, allocs, s.base*1.10, s.base)
+		}
+	}
+}
+
 func TestNoRecordAllocRegression(t *testing.T) {
 	for _, s := range []struct{ name, json string }{
 		{"record 3 columns", `{"format":"","a":"x","b":"y","c":"z"}`},