From ce40826d516fe927185aefd00c234951bd527429 Mon Sep 17 00:00:00 2001
From: Alexander Wang <alex@terrastruct.com>
Date: Wed, 29 Jan 2025 16:25:30 -0700
Subject: [PATCH] ensure unique diagram hash based on appearance

---
 d2lib/d2.go                             |  9 ++++
 docs/examples/lib/1-d2lib/d2lib_test.go | 56 +++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/d2lib/d2.go b/d2lib/d2.go
index a50e1a226..39613caec 100644
--- a/d2lib/d2.go
+++ b/d2lib/d2.go
@@ -77,6 +77,15 @@ func Compile(ctx context.Context, input string, compileOpts *CompileOptions, ren
 
 	d, err := compile(ctx, g, compileOpts, renderOpts)
 	if d != nil {
+		if config == nil {
+			config = &d2target.Config{}
+		}
+		// These are fields that affect a diagram's appearance, so feed them back
+		// into diagram.Config to ensure the hash computed for CSS styling purposes
+		// is unique to its appearance
+		config.ThemeID = renderOpts.ThemeID
+		config.DarkThemeID = renderOpts.DarkThemeID
+		config.Sketch = renderOpts.Sketch
 		d.Config = config
 	}
 	return d, g, err
diff --git a/docs/examples/lib/1-d2lib/d2lib_test.go b/docs/examples/lib/1-d2lib/d2lib_test.go
index 53b3d5bcc..30a1b923e 100644
--- a/docs/examples/lib/1-d2lib/d2lib_test.go
+++ b/docs/examples/lib/1-d2lib/d2lib_test.go
@@ -1,9 +1,65 @@
 package main
 
 import (
+	"context"
 	"testing"
+
+	"oss.terrastruct.com/d2/d2graph"
+	"oss.terrastruct.com/d2/d2layouts/d2dagrelayout"
+	"oss.terrastruct.com/d2/d2lib"
+	"oss.terrastruct.com/d2/d2renderers/d2svg"
+	"oss.terrastruct.com/d2/d2themes/d2themescatalog"
+	"oss.terrastruct.com/d2/lib/log"
+	"oss.terrastruct.com/d2/lib/textmeasure"
+	"oss.terrastruct.com/util-go/assert"
+	"oss.terrastruct.com/util-go/go2"
 )
 
 func TestMain_(t *testing.T) {
 	main()
 }
+
+func TestConfigHash(t *testing.T) {
+	var hash1, hash2 string
+	var err error
+
+	{
+		ruler, _ := textmeasure.NewRuler()
+		layoutResolver := func(engine string) (d2graph.LayoutGraph, error) {
+			return d2dagrelayout.DefaultLayout, nil
+		}
+		renderOpts := &d2svg.RenderOpts{
+			Pad:     go2.Pointer(int64(5)),
+			ThemeID: &d2themescatalog.GrapeSoda.ID,
+		}
+		compileOpts := &d2lib.CompileOptions{
+			LayoutResolver: layoutResolver,
+			Ruler:          ruler,
+		}
+		ctx := log.WithDefault(context.Background())
+		diagram, _, _ := d2lib.Compile(ctx, "x -> y", compileOpts, renderOpts)
+		hash1, err = diagram.HashID()
+		assert.Success(t, err)
+	}
+
+	{
+		ruler, _ := textmeasure.NewRuler()
+		layoutResolver := func(engine string) (d2graph.LayoutGraph, error) {
+			return d2dagrelayout.DefaultLayout, nil
+		}
+		renderOpts := &d2svg.RenderOpts{
+			Pad:     go2.Pointer(int64(5)),
+			ThemeID: &d2themescatalog.NeutralGrey.ID,
+		}
+		compileOpts := &d2lib.CompileOptions{
+			LayoutResolver: layoutResolver,
+			Ruler:          ruler,
+		}
+		ctx := log.WithDefault(context.Background())
+		diagram, _, _ := d2lib.Compile(ctx, "x -> y", compileOpts, renderOpts)
+		hash2, err = diagram.HashID()
+		assert.Success(t, err)
+	}
+
+	assert.NotEqual(t, hash1, hash2)
+}