fix empty base for animations

ci/release/changelogs/next.md

@@ -14,3 +14,4 @@
 - Shadow is cut off when `--pad` is 0. Thank you @LeonardsonCC ! [#1326](https://github.com/terrastruct/d2/pull/1326)
 - Fixes grid layout overwriting label placements for nested objects. [#1345](https://github.com/terrastruct/d2/pull/1345)
 - Fixes fonts not rendering correctly on certain platforms. Thanks @mikeday for identifying the solution. [#1356](https://github.com/terrastruct/d2/pull/1356)
+- Fixes folders not rendering in animations (`--animate-interval`) [#1357](https://github.com/terrastruct/d2/pull/1357)

d2cli/main.go

@@ -641,10 +641,9 @@ func render(ctx context.Context, ms *xmain.State, compileDur time.Duration, plug
 			ms.Log.Success.Printf("successfully compiled %s to %s in %s", ms.HumanPath(inputPath), ms.HumanPath(boardOutputPath), dur)
 		}
 		boards = append([][]byte{out}, boards...)
-		return boards, nil
 	}
 
-	return nil, nil
+	return boards, nil
 }
 
 func _render(ctx context.Context, ms *xmain.State, plugin d2plugin.Plugin, opts d2svg.RenderOpts, outputPath string, bundle, forceAppendix bool, page playwright.Page, ruler *textmeasure.Ruler, diagram *d2target.Diagram) ([]byte, error) {

e2etests-cli/main_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
@@ -76,6 +77,30 @@ func TestCLI_E2E(t *testing.T) {
 				assert.TestdataDir(t, filepath.Join(dir, "empty-layer"))
 			},
 		},
+		{
+			// Skip the empty base board so the animation doesn't show blank for 1400ms
+			name: "empty-base",
+			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {
+				writeFile(t, dir, "empty-base.d2", `steps: {
+  1: {
+    a -> b
+  }
+  2: {
+    b -> d
+    c -> d
+  }
+  3: {
+    d -> e
+  }
+}`)
+
+				err := runTestMain(t, ctx, dir, env, "--animate-interval=1400", "empty-base.d2")
+				assert.Success(t, err)
+				svg := readFile(t, dir, "empty-base.svg")
+				assert.Testdata(t, ".svg", svg)
+				assert.Equal(t, 3, getNumBoards(string(svg)))
+			},
+		},
 		{
 			name: "animation",
 			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {
@@ -447,3 +472,9 @@ func removeD2Files(tb testing.TB, dir string) {
 func testdataIgnoreDiff(tb testing.TB, ext string, got []byte) {
 	_ = diff.Testdata(filepath.Join("testdata", tb.Name()), ext, got)
 }
+
+// getNumBoards gets the number of boards in an SVG file through a non-robust pattern search
+// If the renderer changes, this must change
+func getNumBoards(svg string) int {
+	return strings.Count(svg, `class="d2`)
+}