print msg when png and layout in progress

ci/release/changelogs/next.md

@@ -6,6 +6,7 @@
 
 - `--browser` flag on CLI controls `BROWSER` environment variable for not opening browser in watch mode. [#1052](https://github.com/terrastruct/d2/pull/1052)
 - `elk` layout containers no longer overlap the label with children. [#1055](https://github.com/terrastruct/d2/pull/1055)
+- Message emitted by CLI when a particular stage is taking a long time. [#1058](https://github.com/terrastruct/d2/pull/1058)
 - `<title>` attribute of HTML in watch mode is the base file name, instead of the whole path. [#1054](https://github.com/terrastruct/d2/pull/1054)
 
 #### Bugfixes ⛑️

d2cli/main.go

@@ -27,6 +27,7 @@ import (
 	"oss.terrastruct.com/d2/d2target"
 	"oss.terrastruct.com/d2/d2themes"
 	"oss.terrastruct.com/d2/d2themes/d2themescatalog"
+	"oss.terrastruct.com/d2/lib/background"
 	"oss.terrastruct.com/d2/lib/imgbundler"
 	ctxlog "oss.terrastruct.com/d2/lib/log"
 	"oss.terrastruct.com/d2/lib/pdf"
@@ -289,10 +290,17 @@ func compile(ctx context.Context, ms *xmain.State, plugin d2plugin.Plugin, sketc
 	if sketch {
 		opts.FontFamily = go2.Pointer(d2fonts.HandDrawn)
 	}
+
+	cancel := background.Repeat(func() {
+		ms.Log.Info.Printf("compiling & running layout algorithms...")
+	}, time.Second*5)
+	defer cancel()
+
 	diagram, g, err := d2lib.Compile(ctx, string(input), opts)
 	if err != nil {
 		return nil, false, err
 	}
+	cancel()
 
 	pluginInfo, err := plugin.Info(ctx)
 	if err != nil {

lib/background/background.go

@@ -0,0 +1,28 @@
+package background
+
+import "time"
+
+func Repeat(do func(), interval time.Duration) (cancel func()) {
+	t := time.NewTicker(interval)
+	done := make(chan struct{})
+
+	go func() {
+		defer t.Stop()
+		for {
+			select {
+			case <-t.C:
+				do()
+			case <-done:
+				return
+			}
+		}
+	}()
+
+	stopped := false
+	return func() {
+		if !stopped {
+			stopped = true
+			close(done)
+		}
+	}
+}

lib/png/png.go

@@ -5,6 +5,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"strings"
+	"time"
 
 	_ "embed"
 
@@ -13,6 +14,7 @@ import (
 	pngstruct "github.com/dsoprea/go-png-image-structure/v2"
 	"github.com/playwright-community/playwright-go"
 
+	"oss.terrastruct.com/d2/lib/background"
 	"oss.terrastruct.com/d2/lib/version"
 	"oss.terrastruct.com/util-go/xmain"
 )
@@ -82,6 +84,11 @@ var genPNGScript string
 const pngPrefix = "data:image/png;base64,"
 
 func ConvertSVG(ms *xmain.State, page playwright.Page, svg []byte) ([]byte, error) {
+	cancel := background.Repeat(func() {
+		ms.Log.Info.Printf("converting to PNG...")
+	}, time.Second*5)
+	defer cancel()
+
 	encodedSVG := base64.StdEncoding.EncodeToString(svg)
 	pngInterface, err := page.Evaluate(genPNGScript, "data:image/svg+xml;charset=utf-8;base64,"+encodedSVG)
 	if err != nil {